Earth-logs

Gravity survey reveals signs of Archaean tectonics in Canadian Shield

Published on October 10, 2025October 13, 2025 by zooks777Leave a comment

Much of the Archaean Eon is represented by cratons, which occur at the core of continental parts of tectonic plates. Having low geothermal heat flow they are the most rigid parts of the continental crust. The Superior Craton is an area that makes up much of the eastern part of the Canadian Shield, and formed during the Late Archaean from ~4.3 to 2.6 billion years (Ga) ago. Covering an area in excess of 1.5 million km², it is the world’s largest craton. One of its most intensely studied components is the Abitibi Terrane, which hosts many mines. A granite-greenstone terrain, it consists of volcano-sedimentary supracrustal rocks in several typically linear greenstone belts separated by areas of mainly intrusive granitic bodies. Many Archaean terrains show much the same ‘stripey’ aspect on the grand scale. Greenstone belts are dominated by metamorphosed basaltic volcanic rock, together with lesser proportions of ultramafic lavas and intrusions, and overlying metasedimentary rocks, also of Archaean age. Various hypotheses have been suggested for the formation of granite-greenstone terrains, the latest turning to a process of ‘sagduction’. However the relative flat nature of cratonic areas tells geologists little about their deeper parts. They tend to have resisted large-scale later deformation by their very nature, so none have been tilted or wholly obducted onto other such stable crustal masses during later collisional tectonic processes. Geophysics does offer insights however, using seismic profiling, geomagnetic and gravity surveys.

The Geological Survey of Canada has produced masses of geophysical data as a means of coping with the vast size and logistical challenges of the Canadian Shield. Recently five Canadian geoscientists have used gravity data from the Canadian Geodetic Survey to model the deep crust beneath the huge Abitibi granite-greenstone terrain, specifically addressing variations in its density in three dimensions. They also used cross sections produced by seismic reflection and refraction data along 2-D survey lines (Galley, C. et al. 2025. Archean rifts and triple-junctions revealed by gravity modeling of the southern Superior Craton. Nature Communications, v. 16, article 8872; DOI: 10.1038/s41467-025-63931-z). The group found that entirely new insights emerge from the variation in crustal density down to its base at the Moho (Mohorovičić discontinuity). These data show large linear bulges in the Moho separated by broad zones of thicker crust.

Geology of the Abitibi Terrane (upper),; Depth to the Moho beneath the Abitibi Terrane with rifts and VMS deposits superimposed (lower). Credit: After Galley et al. Figs 1 and 5.

Galley et al. suggest that the zones are former sites of lithospheric extensional tectonics and crustal thinning: rifts from which ultramafic to mafic magmas emerged. They consider them to be akin to modern mid-ocean and continental rifts. Most of the rifts roughly parallel the trend of the greenstone belts and the large, long-lived faults that run west to east across the Abitibi Terrain. This suggests that rifts formed under the more ductile lithospheric condition of the Neoarchaean set the gross fabric of the granites and greenstones. Moreover, there are signs of two triple junctions where three rifts converge: fundamental features of modern plate tectonics. However, both rifts and junctions are on a smaller scale than those active at present. The rift patterns suggest plate tectonics in miniature, perhaps indicative of more vigorous mantle convection during the Archaean Eon.

There is an interesting spin-off. The Abitibi Terrane is rich in a variety of mineral resources, especially volcanic massive-sulfide deposits (VMS). Most of them are associated with the suggested rift zones. Such deposits form through sea-floor hydrothermal processes, which Archaean rifting and triple junctions would have focused to generate clusters of ‘black smokers’ precipitating large amounts of metal sulfides. Galley et al’s work is set to be applied to other large cratons, including those that formed earlier in the Archaean: the Pilbara and Kaapvaal cratons of Australia and South Africa. That could yield better insights into earlier tectonic processes and test some of the hypotheses proposed for them

See also: Archaean Rifts, Triple Junctions Mapped via Gravity Modeling. Scienmag, 6 October 2025

A possible Chinese ancestor for Denisovans, Neanderthals and modern humans

Published on September 30, 2025September 30, 2025 by zooks777Leave a comment

Assigning human fossils older than around 250 ka to different groups of the genus Homo depends entirely on their physical features. That is because ancient DNA has yet to be found and analysed from specimens older than that. The phylogeny of older human remains is also generally restricted to the bones that make up their heads; 21 that are fixed together in the skull and face, plus the moveable lower jaw or mandible. Far more teeth than crania have been discovered and considerable weight is given to differences in human dentition. Teeth are not bones, but they are much more durable, having no fibrous structure and vary a great deal. The main problem for palaeoanthropologists is that living humans are very diverse in their cranial characteristics, and so it is reasonable to infer that all ancient human groups were characterised by such polymorphism, and may have overlapped in their physical appearance. A measure of this is that assigning fossils to anatomically modern humans, i.e. Homo sapiens, relies to a large extent on whether or not their lower mandible juts out to define a chin. All earlier hominins and indeed all other living apes might be regarded as ‘chinless wonders’! This pejorative term suggests dim-wittedness to most people, and anthropologists have had to inure themselves to such crude cultural conjecture.

The extraction, sequencing and comparison of ancient DNA from human fossils since 2010 has revealed that three distinct human species coexisted and interbred in Eurasia. Several well preserved examples of ancient Neanderthals and anatomically modern humans (AMH) have had their DNA sequenced, but a Denisovan genome has only emerged from a few bone fragments from the Denisova Cave in western Siberia. Whereas Neanderthals have well-known robust physical characters, until 2025 palaeoanthropologists had little idea of what Denisovans may have looked like. Then proteins and, most importantly, mitochondrial DNA (mtDNA) were extracted from a very robust skull found around 1931 in Harbin, China, dated at 146 ka. Analysis of the mtDNA and proteins, from dental plaque and bone respectively, reveal that the Harbin skull is likely to be that of a Denisovan. Previously it had been referred to as Homo longi, or ‘Dragon Man’, along with several other very robust Chinese skulls of a variety of ages.

The distorted Yunxian cranium (right) and its reconstruction (middle) [Credit: Guanghui Zhao] compared with the Harbin Denisovan cranium (left) [Hebei Geo University]

The sparse genetic data have been used to suggest the times when the three different coexisting groups diverged. DNA in Y chromosomes from Denisovans and Neanderthals suggest that the two lineages split from a common ancestor around 700 ka ago, whereas Neanderthals and modern humans diverged genetically at about 370 ka. Yet the presence of sections of DNA from both archaic groups in living humans and the discovery that a female Neanderthal from Denisova cave had a Neanderthal mother and a Denisovan father reveals that all three were interfertile when they met and interacted. Such admixture events clearly have implications for earlier humans. There are signs of at least 6 coexisting groups as far back as the Middle Pleistocene (781 to 126 ka), referred to by some as the ‘muddle in the middle’ because such an association has increasingly mystified palaeoanthropologists. A million-year-old, cranium found near Yunxian in Hubei Province, China, distorted by the pressure of sediments in which it was buried, has been digitally reconstructed.

This reconstruction encouraged a team of Chinese scientists, together with Chris Stringer of the UK Museum of Natural History, to undertake a complex statistical study of the Yunxian cranium. Their method compares it with anatomical data for all members of the genus Homo from Eurasia and Africa, i.e. as far back as the 2.4 Ma old H. habilis (Xiabo Feng and 12 others 2025. The phylogenetic position of the Yunxian cranium elucidates the origin of Homo longi and the Denisovans. Science, v. 389, p. 1320-1324; DOI: 10.1126/science.ado9202). The study has produced a plausible framework that suggests that the five large-brained humans known from 800 ka ago – Homo erectus (Asian), H. heidelbergensis, H. longi (Denisovans), H. sapiens, and H. neanderthalensis – began diverging from one another more than a million years ago. The authors regard the Yuxian specimen as an early participant in that evolutionary process. The fact that at least some remained interfertile long after the divergence began suggests that it was part of the earlier human evolutionary process. It is also possible that the repeated morphological divergence may stem from genetic drift. That process involves small populations with limited genetic diversity that are separated from other groups, perhaps by near-extinction in a population bottleneck or as a result of the founder effect when a small group splits from a larger population during migration. The global population of early humans was inevitably very low, and migrations would dilute and fragment each group’s gene pool.

The earliest evidence for migration of humans out of Africa emerged from the discovery of five 1.8 Ma old crania of H. erectus at Dmanisi to the east of the Black Sea in Georgia. similar archaic crania have been found in eastern Eurasia, especially China, at various localities with Early- to Middle Pleistocene dates. The earliest European large-brained humans – 1.2 to 0.8 Ma old H. antecessor from northern Spain – must have migrated a huge distance from either Africa or from eastern Eurasia and may have been a product of the divergence-convergence evolutionary framework suggested by Xiabo Feng and colleagues. Such a framework implies that even earlier members of what became the longi, heidelbergensis, neanderthalensis, and sapiens lineages may await either recognition or discovery elsewhere. But the whole issue raises questions about the widely held view that Homo sapiens first appeared 300 ka ago in North Africa and then populated the rest of that continent. Was that specimen a migrant from Eurasia or from elsewhere in Africa? The model suggested by Xiabo Feng and colleagues is already attracting controversy, but that is nothing new among palaeoanthropologists. Yet it is based on cutting edge phylogeny derived from physical characteristics of hominin fossils: the traditional approach by all palaeobiologists. Such disputes cannot be resolved without ancient DNA or protein assemblages. But neither is a completely hopeless task, for Siberian mammoth teeth have yielded DNA as old as 1.2 Ma and the record is held by genetic material recovered from sediments in Greenland that are up to 2.1 Ma old. The chances of pushing ancient human DNA studies back to the ‘muddle’ in the Middle Pleistocene depend on finding human fossils at high latitudes in sediments of past glacial maxima or very old permafrost, for DNA degrades more rapidly as environmental temperature rises.

See also: Natural History Museum press release. Analysis of reconstructed ancient skull pushes back our origins by 400,000 years to more than one million years ago. 25 September 2025; Bower, B. 2025. An ancient Chinese skull might change how we see our human roots. ScienceNews, 25 September 2025; Ghosh, P. 2025. Million-year-old skull rewrites human evolution, scientists claim. The Guardian, 25 September 2025

Ancient mining pollutants in river sediments reveal details of early British economic history

Published on September 22, 2025September 20, 2025 by zooks777Leave a comment

People have been mining in Britain since Neolithic farmers opened the famous Grimes Graves in Norfolk – a large area dotted with over 400 pits up to to 13 metres deep. The target was a layer of high quality black flint in a Cretaceous limestone known as The Chalk. Later Bronze Age people in Wales and Cornwall drove mine shafts deeper underground to extract copper and tin ores to make the alloy bronze. The Iron Age added iron ore to the avid search for sources of metals. The production and even export of metals and ores eventually attracted the interest of Rome. Roman invasion in 43 CE during the reign of Claudius annexed most of England and Wales to create the province of Britannia. This lasted until the complete withdrawal of Roman forces around 410 CE. Roman imperialism and civilisation depended partly on lead for plumbing and silver coinage to pay its legionaries. Consequently, an important aspect in Rome’s four-century hegemony was mining, especially for lead ore, as far north as the North Pennines. This littered the surface in mining areas with toxic waste. Silver occurs in lead ore in varying proportions. In the Bronze Age early metallurgists extracted silver from smelted, liquid lead by a process known as cupellation. The molten Pb-Ag alloy is heated in air to a much higher temperature than its melting point, when lead reacts with oxygen to form a solid oxide (PbO) and silver remains molten.

Mine waste in the North Pennine orefield of England. Credit: North Pennines National Landscape

Until recently, historians believed that the fall of the Western Empire brought economic collapse to Britain. Yet archaeologists have revealed that what was originally called the “Dark Ages” (now Early Medieval Period) had a thriving culture among both the remaining Britons and Anglo Saxon immigrants. A means of tracking economic activity is to measure the amount of pollutants from mining waste at successive levels in the alluvium of rivers that flow through orefields. Among the best known in Britain is the North Pennine Orefield of North Yorkshire and County Durham through which substantial rivers flow eastwards, such as the River Ure that flows through the heavily mined valley of Wensleydale. A first attempt at such geochemical archaeology has been made by a British team led by Christopher Loveluck of Nottingham University (Loveluck, C.P. and 10 others 2025. Aldborough and the metals economy of northern England, c. AD 345–1700: a new post-Roman narrative. Antiquity: FirstView, online article; DOI: 10.15184/aqy.2025.10175). Aldborough in North Yorkshire – sited on the Romano-British town of Isurium Brigantum – lies in the Vale of York, a large alluvial plain. The River Ure has deposited sands, silts and muds in the area since the end of the last Ice Age, 11 thousand years ago.

Loveluck et al. extracted a 6 m core from the alluvium on the outskirts of Aldborough, using radiocarbon and optically-stimulated luminescence of quartz grains to calibrate depth to age in the sediments. The base of the core is Mesolithic in age (~6400 years ago) and extends upwards to modern times, apparently in an unbroken sequence. Samples were taken for geochemical analysis every 2 cm through the upper 1.12 m of the core, which spans the Roman occupation (43 to 410 CE), the early medieval (420 to 1066 CE), medieval (1066 to 1540 CE), post-medieval (1540 to 1750 CE) and modern times (1750 CE to present). Each sample was analysed for 56 elements using mass spectrometry; lead, silver, copper, zinc, iron and arsenic being the elements of most interest in this context. Other data gleaned from the sediment are those of pollen, useful in establishing climate and ecological changes. Unfortunately, the metal data begin in 345 CE, three centuries after the Roman invasion, by which time occupation and acculturation were well established. The authors assume that Romans began the mining in the North Pennines. They say nothing about the pre-mining levels of pollution from the upstream orefield nor mining conducted by the Iron Age Brigantes. For this kind of survey, it is absolutely essential that a baseline is established for the pollution levels under purely natural conditions. The team could have analysed sediment from the Mesolithic when purely natural weathering, erosion and transport could safely be assumed, but they seem not to have done that.

The team has emphasised that their data suggest that mining for lead continued and even increased through the ‘Dark Ages’ rather than declining, in an economic ‘slump’ once the Romans left, as previous historians have suggested. Lead pollution continued at roughly the same levels as during the Roman occupation through the Early Medieval Period and then rose to up to three times higher after the late 14^th century. The data for silver are different. The Ag data from Aldborough show a large ‘spike’ in 427 to 427 CE. Interestingly this is after the Roman withdrawal. Its level in alluvium then ‘flatlines’ at low abundances until the beginning of the 14^th century when again there is a series of ‘booms’. This seems to me to mark sudden spells of coining, after the Romans left perhaps first to ensure a money economy remained possible, and then as a means of funding wars with the French in the 14^th century. The authors also found changing iron abundances, which roughly double from low Roman levels to an Early Medieval peak and then fall in the 11^th century: a result perhaps of local iron smelting. The overall patterns for zinc and copper differ substantially from those of lead, as does that for arsenic which roughly follows the trend for iron. That might indicate that local iron production was based on pyrite (FeS₂) which can contain arsenic at moderate concentrations: pyrite is a common mineral in the ore bodies of the North Pennines’ The paper by Loveluck et al. is worth reading as a first attempt to correlate stratigraphic geochemistry data with episodes in British and, indeed, wider European history. But I think it has several serious flaws, beyond the absence of any pre-Roman geochemical baseline, as noted above. No data are presented for barium (Ba) and fluorine (F) derived from the gangue minerals baryte (BaSO₄) and fluorite (CaF₂), which outweigh lead and zinc sulfides in North Pennine ore bodies, yet had no use value until the Industrial Revolution. They would have made up a substantial proportion of mine spoil heaps – useful ores would have been picked out before disposal of gangue – whose erosion, comminution and transport would make contributions to downstream deposition of alluvium consistent with the pace of mining. That is: Ba and F data would be far better guides to industrial activity. There is a further difficulty with such surveys in northern Britain. The whole of the upland areas were subjected to repeated glaciation, which would have gathered exposed ore and gangue and dumped it in till, especially in the numerous moraines exposed in valleys such as Wensleydale. Such sources may yield sediment in periods of naturally high erosion during floods. Finally, the movement of sediment downstream is obviously not immediate, especially when waste is disposed in large dumps near mines Therefore phases of active mining may not contribute increased toxic waste far downstream until decades or even centuries later. These factors could easily have been clarified by a baseline study from earlier archaeological periods when mining was unlikely, into which the Aldborough alluvium core penetrates

Human interventions in geological processes

Published on August 29, 2025 by zooks777Leave a comment

During the Industrial Revolution not only did the emission of greenhouse gases by burning fossil fuels start to increase exponentially, but so too did the movement of rock and sediment to get at those fuels and other commodities demanded by industrial capital. In the 21^st century about 57 billion tons of geological materials are deliberately moved each year. Global population followed the same trend, resulting in increasing expansion of agriculture to produce food. Stripped of its natural cover on every continent soil began to erode at exponential rates too. The magnitude of human intervention in natural geological cycles has become stupendous, soil erosion now shifting on a global scale about 75 billion tons of sediment, more than three times the estimated natural rate of surface erosion. Industrial capital together with society as a whole also creates and dumps rapidly growing amounts of solid waste of non-geological provenance. The Geological Society of America’s journal Geology recently published two research papers that document how capital is transforming the Earth.

Dust Bowl conditions on the Minnesota prairies during the 1930s.

One of the studies is based on sediment records in the catchment of a tributary of the upper Mississippi River. The area is surrounded by prairie given over mainly to wheat production since the mid 19^th century. The deep soil of the once seemingly limitless grassland developed by the prairie ecosystem is ideal for cereal production. In the first third of the 20^th century the area experienced a burst of erosion of the fertile soil that resulted from the replacement of the deep root systems of prairie grasses by shallow rooted wheat. The soil had formed from the glacial till deposited by the Laurentide ice sheet than blanketed North America as far south as New York and Chicago. Having moved debris across almost 2000 km of low ground, the till is dominated by clay- and silt-sized particles. Once exposed its sediments moved easily in the wind. Minnesota was badly affected by the ‘Dust Bowl’ conditions of the 1930s, to the extent that whole towns were buried by up to 4.5 metres of aeolian sediment. For the first time the magnitude of soil erosion compared with natural rates has been assessed precisely by dating layers of alluvium deposited in river terraces of one of the Mississippi’s tributaries (Penprase, S.B. et al. 2025. Plow versus Ice Age: Erosion rate variability from glacial–interglacial climate change is an order of magnitude lower than agricultural erosion in the Upper Mississippi River Valley, USA. Geology, v. 53, p. 535-539; DOI: 10.1130/G52585.1).

Shanti Penprase of the University of Minnesota and her colleagues were able to date the last time sediment layers at different depths in terraces were exposed to sunlight and cosmic rays, by analysing optically stimulated luminescence (OSL) and cosmogenic ¹⁰Be content of quartz grains from the alluvium. The data span the period since the Last Glacial Maximum 20 thousand years ago during which the ecosystem evolved from bare tundra through re-vegetation to pre-settlement prairie. They show that post-glacial natural erosion had proceeded at around 0.05 mm yr^-1 from a maximum of 0.07 when the Laurentide Ice Sheet was at its maximum extent. Other studies have revealed that after the area was largely given over to cereal production in the 19^th century erosion rates leapt to as high as 3.5 mm yr^-1 with a median rate of 0.6 mm yr^-1, 10 to 12 times that of post-glacial times. It was the plough and single-crop farming introduced by non-indigenous settlers that accelerated erosion. Surprisingly, advances in prairie agriculture since the Dust Bowl have not resulted in any decrease in soil erosion rates, although wind erosion is now insignificant. The US Department of Agriculture considers the loss of one millimetre per year to be ‘tolerable’: 14 times higher than the highest natural rate in glacial times.

The other paper has a different focus: how human activities may form solid rock. The world over, a convenient means of disposing of unwanted material in coastal areas is simply to dump waste in the sea. That has been happening for centuries, but as for all other forms of anthropogenic waste disposal the volumes have increased at an exponential rate. The coast of County Durham in Britain began to experience marine waste disposal when deep mines were driven into Carboniferous Coal Measures hidden by the barren Permian strata that rest unconformably upon them. Many mines extended eastwards beneath the North Sea, so it was convenient to dump 1.5 million tons of waste rock annually at the seaside. The 1971 gangster film Get Carter starring Michael Caine includes a sequence showing ‘spoil’ pouring onto the beach below Blackhall colliery, burying the corpse of Carter’s rival. The nightmarish, 20 km stretch of grossly polluted beach between Sunderland and Hartlepool also provided a backdrop for Alien 3. Historically, tidal and wave action concentrated the low-density coal in the waste at the high-water mark, to create a free resource for locals in the form of ‘sea coal’ as portrayed in Tom Scott Robson’s 1966 documentary Low Water. Closure of the entire Duham coalfield in the 1980s and ‘90s halted this pollution and the coast is somewhat restored – at a coast of around £10 million.

‘Anthropoclastic’ conglomerate formed from iron-smelting slag dumped on the West Cumbrian coast. It incorporates artefacts as young as the 1980s, showing that it was lithified rapidly. Credit: Owen et al, Supplementary Figure 2

On the West Cumbrian coast of Britain another industry dumped millions of tons of waste into the sea. In the case it was semi-molten ‘slag’ from iron-smelting blast furnaces poured continuously for 130 years until steel-making ended in the 1980s. Coastal erosion has broken up and spread an estimated 27 million cubic metres of slag along a 2 km stretch of beach. Astonishingly this debris has turned into a stratum of anthropogenic conglomerate sufficiently well-bonded to resist storms (Owen, A., MacDonald, J.M. & Brown, D.J 2025. Evidence for a rapid anthropoclastic rock cycle. Geology, v. 53, p. 581–586; DOI: 10.1130/G52895.1). The conglomerate is said by the authors to be a product of ‘anthropoclastic’ processes. Its cementation involves minerals such as goethite, calcite and brucite. Because the conglomerate contains car tyres, metal trouser zips, aluminium ring-pulls from beer cans and even coins lithification has been extremely rapid. One ring-pull has a design that was not used in cans until 1989, so lithification continued in the last 35 years.

Furnace slag ‘floats’ on top of smelted iron and incorporates quartz, clays and other mineral grains in iron ore into anhydrous calcium- and magnesium-rich aluminosilicates. This purification is achieved deliberately by including limestone as a fluxing agent in the furnace feed. The high temperature reactions are similar to those that produce aluminosilicates when cement is manufactured. Like them, slag breaks down in the presence of water to recrystallis in hydrated form to bond the conglomerate. This is much the same manner as concrete ‘sets’ over a few days and weeks to bind together aggregate. There is vastly more ‘anthropoclastic’ rock in concrete buildings and other modern infrastructure. Another example is tarmac that coats millions of kilometres of highway.

See also: Howell, E. 2025. Modern farming has carved away earth faster than during the ice age. Science, v. 388

Earliest hominin occupation of Sulawesi and crossing of an ocean barrier

Published on August 12, 2025August 12, 2025 by zooks777Leave a comment

Regular readers of Earth-logs will recall that the islands of Indonesia were reached by the archaic humans Homo erectus and H. floresiensis at least a million years ago. Anatomical comparison of their remains suggest that the diminutive H. floresiensis probably evolved from H. erectus under the stress of being stranded on the small, resource-poor island of Flores: a human example of island dwarfism. In fact there are anatomically modern humans (AMH) living on Flores that seem to have evolved dwarfism in the same way since AMH first arrived there between 50 and 5 ka. Incidentally, H. erectus fossils and artefacts were found by Eugene Dubois in the late 19^th century at a famous site near Trinil in Java. In 2014, turned out that H. erectus had produced the earliest known art – zig-zag patterns on freshwater clam shells – between 540 and 430 ka ago. The episodic falls in global sea level due to massive accumulations of ice on land during successive Pleistocene glacial episodes aided migration by producing connections between the islands of SE Asia. They created a huge area of low-lying dryland known as ‘Sundaland’. The islands’ colonisation by H. erectus was made easy, perhaps inevitable.

The interconnection of SE Asian islands to form Sundaland (yellow) when sea level was 120 m lower than today. Even at that extreme the island of Sulawesi remained isolated by deep ocean water. Credit: based on Hakim et al Fig 1.

However, Flores and islands further east are separated from those to the west by a narrow but very deep strait. It channels powerful currents that are hazardous to small-boat crossings even today. Most palaeoanthropologists consider the colonisation of Flores by H. erectus most likely to have resulted by accident, reckoning that they were incapable of planning a crossing and building suitable craft. For AMH to have reached New Guinea and Australia around 60 ka ago, they must have developed sturdy craft and sea-faring skills. This paradigm suggests that the evolution of AMH, and thus their eventual occupation of all continents except Antarctica, must have involved a revolutionary ‘leap’ in their cognitive ability just before they left Africa. That view has been popularised by the presenter (Ella Al-Shamahi) of the 2025 BBC Television series Human – now on BBC iPlayer (requires viewers to create a free account) – in its second episode Into the Unknown. [The idea of a cognitive leap that ushered in the almost worldwide migration of anatomically modern humans was launched in 1995 by controversial anthropologist Chris Knight of University College London].

Flaked artefact, about the length of a human thumb, made of chert from excavations at Calio on Sulawesi, dated at 1.02 Ma. Credit: based on Hakim et al Fig 2

The large and peculiarly-shaped island of Sulawesi, also part of Indonesia, is notable for being the location of the earliest known figurative art; a cave painting of a Sulawesi warty pig, dated to at least 45.5 ka ago. Indonesian and Australian archaeologists working at a site near Calio in northern Sulawesi unearthed stone artefacts deep in river-terrace gravels that contain fossils of extinct pigs and dwarf elephants (Hakim, B. and 26 others 2025. Hominins on Sulawesi during the Early Pleistocene. Nature, v. 644;DOI: 10.1038/s41586-025-09348-6). The tools were struck from pebbles of hard fine-grained rocks by flaking to produce sharp edges. A combination of dating techniques – palaeomagnetism, uranium-series and electron-spin resonance – on the terrace sediments and fossils in them yielded ages ranging from 1.04 to 1.48 Ma; far older than the earliest known presence of AMH on the island (73–63 ka). The dates for an early human presence on Sulawesi tally with those from Flores. The tool makers were probably H. erectus. To reach the island from Sundaland at a time when global sea level was 120 m lower than at present would have required crossing more than 50 km of open water. It seems unlikely that such a journey could have been accidental. The migrants would have needed seaworthy craft; possibly rafts. Clearly the AMH crossings to New Guinea around 60 thousand years ago would have been far more daunting. Both land masses would have been below the horizon of any point of departure from the Indonesian archipelago, even with island ‘hopping’. Yet the Sulawesi discovery, combined with the plethora of islands both large and small, suggests that the earlier non-AMH inhabitants of Indonesia potentially could have spread further at times of very low sea level.

See also: Brumm, A. t al. 2025. This stone tool is over 1 million years old. How did its maker get to Sulawesi without a boat? The Conversation, 6 August 2025

Did the Meteor Crater impact in Arizona dam the Grand Canyon 56 thousand years ago?

Published on July 31, 2025July 30, 2025 by zooks777Leave a comment

Meteor Crater, Arizona, USA. Credit: Travel in USA

Meteor Crater, 60 km east of Flagstaff in Arizona, USA, is probably the most visited site of an impact by an extraterrestrial object. At 1.3 km across it isn’t especially big, but it is exceptionally well preserved, having formed a mere 55.6 ka ago. Apart from its shape its impact origin is proved by its rim, which shows overturning and inversion of strata that it penetrated. The 40 metre diameter nickel-iron object that did the damage arrived at a speed around 13 km s^-1 and delivered kinetic energy equivalent to an explosion of 10 million tons of TNT. This was sufficient to vaporise the body, except for a few fragments. Impressive as that is, the impact was tiny compared with others known on Earth, such as the Chicxulub impact that ended the Mesozoic Era 60 Ma ago. Nevertheless, the surface blast would have sterilised an area up to 1000 km² around the impact, i.e. up to 17 km in all directions. Yet, most of the impact energy would have affected the surrounding crust. It’s a place worth visiting.

The other must-see site in northern Arizona is the Grand Canyon, some 100 km north of Flagstaff by train, and about 320 km by road. Unlike Meteor Crater, whose origins were well established more than 50 years ago, the Grand Canyon still draws research teams to study the geology of the rock formations through which it cuts and the geomorphological processes that formed it. Several expeditions have examined caves high above the level of the Colorado River that has cut the Canyon since the start of the Pliocene Epoch, some 5 Ma ago. One objective of this research has been to document past flooding, due to the massive landslides and rock falls that must have occurred as cliffs became unstable during canyon formation. One cave – Stanton’s Cave – is 45 m above the present level of the Colorado: about the height of a 16 storey block of flats. The cave floor is made of well-bedded sand that contains driftwood logs, as do other caves along the canyon. Dating the logs from cave to cave should give at least an idea of the history of flooding and thus cliff collapses. In the case of Stanton’s Cave early radiocarbon dating yielded results close to the maximum that the rapid decay of ¹⁴C makes possible. Such dating at the limit of the technique is imprecise. The oldest existing radiocarbon age in this case is 43.5 ± 1.5 ka from a 1984 study. Since then, this dating technique has advanced considerably.

Fig Remnants of a landslide, subsequently breached, in the Grand Canyon downstream of Stanton’s Cave. Credit: Richard Hereford

Karl Karlstrom – whose father was also entranced by cave deposits in the Grand Canyon in the 1960s – together with colleagues from the US managed to persuade radiocarbon specialists from Australia and New Zealand to improve the sediment dating (Karlstrom, K.E and 11 others 2025. Grand Canyon landslide-dam and paleolake triggered by the Meteor Crater impact at 56 ka. Geology, v. 53, online article; DOI: 10.1130/G53571.1). The new ¹⁴Cage of the logs is 55.25 ± 2.44 ka, confirmed by infrared stimulated luminescence (IRSL) dating of feldspar grains in the cave sand at 56.00 ± 6.39 ka Combined with a new cosmogenic nuclide exposure age of 56.00 ± 2.40 ka for the Meteor Crater ejecta the results are exciting. It looks as if the cliff fall that dammed the Colorado River to fill the cave with sediment coincided with the impact. Crater formation is estimated to have resulted in a seismic event of magnitude 5.4. In such a teetering terrain as the Grand Canyon cliffs, the impact-induced earthquake about 100 km away, even if attenuated to an effective magnitude estimated at 3.5 may have been sufficient to topple part of the cliffs. With cliffs that average 1.6 km high, such a collapse would have displaced sufficient debris to create a substantial barrier to flow of the Colorado River, which is tightly constrained between cliffs. The chaotic debris at the suggested dam site is now partly covered by round river cobbles, suggesting that it was soon overtopped, probably within a thousand years of the cliff collapse.

Because all the dates have substantial imprecision, it is not possible to claim that the authors have proved conclusively a direct connection between impact and cliff collapse. But neither do the age data disprove what is a plausible causal connection.

See also: UNM study finds link between Grand Canyon landslide and Meteor Crater impact. University of New Mexico News 15 July 2025

Evolution of pigmentation in anatomically modern humans of Europe: a new paradigm?

Published on July 28, 2025 by zooks777Leave a comment

The colours of human skin, eyes and hair in living people across the world are determined by variants of genes (alleles) found at the same place on a chromosome. Since chromosomes are inherited from both mother and father, an individual may have the same two alleles (homozygous), or one of each (heterozygous). A dominant allele is always expressed, even if a single copy is present. A recessive allele is only expressed if the individual inherits two copies of it. Most characteristics of individuals result from the interaction of multiple genes, rather than a single gene. A commonly cited example is the coloration of eyes. If we had a single gene for eye colour – that of the iris – that had alleles just for blue (recessive or ‘b’) and one for brown (dominant or ‘B) pigmentation, brown-eyed individuals would have one or two ‘B’ alleles (bB or BB), whereas those with blue eyes would have to have two ‘blue’ alleles (bb). But inheritance is more complicated than that: there are people with green, hazel or grey eyes and even left- and right eyes of different colour. Such examples suggest that there are more than two genes affecting human eye colour, and each must have evolved as a result of mutations. Much the same goes for hair and skin coloration.

A group of scientists from the University of Ferrara in Italy have analysed highly detailed ancient DNA in anatomically modern human remains from Russia (Palaeolithic), Sweden (Mesolithic) and Croatia (Neolithic) to tease out the complexities of pigmentation inheritance. Then they applied a statistical approach learned from that study to predict the likely skin-, eye- and hair pigmentation in 348 less detailed genomes of ancient individuals whose remains date back to 45 Ma ( Silvia Perretti et al, 2025. Inference of human pigmentation from ancient DNA by genotype likelihood. Proceedings of the National Academy of Science, v. 122, article e2502158122; DOI: 10.1073/pnas.2502158122).

An artist’s impression of a Mesolithic woman from southern Denmark (credit: Tom Bjorklund)

All the hunter-gatherer Palaeolithic individuals (12 samples between 45 and 13 ka old) bar one, showed clear signs of dark pigmentation in skin, eyes and hair – the outlier from Russia was probably lighter. Those from the Mesolithic (14 to 4 ka) showed that 11 out of 35 had a light eye colour (Northern Europe, France, and Serbia), but most retained the dark skin and hair expected in descendants of migrants from Africa. Only one 12 ka hunter-gatherer from Sweden had inferred blue eyes, blonde hair, and light skin. The retention of dark pigmentation by European hunter-gatherers who migrated there from Africa has been noted before, using DNA from Mesolithic human remains and in one case from birch resin chewed by a Mesolithic woman. This called into question the hypothesis that high levels of melatonin in skin, which protects indigenous people in Africa from cancers, would result in their producing insufficient vitamin D for good health. That notion supposed that out-of-Africa migrants would quickly evolve paler skin coloration at higher latitudes. It is now known that diets rich in meat, nuts and fungi – staple for hunter-gatherers – provide sufficient vitamin-D for health at high latitudes. A more recent hypothesis is that pale skins may have evolved only after the widespread Neolithic adoption of farming when people came to rely on a diet dominated by cereals that are a poor source of vitamin-D.

However, 132 Neolithic farmers (10 to 4 ka ago) individuals studied by Perretti et al. showed increased diversity in pigmentation, with more frequent light skin tones, yet dark individuals persisted, particularly in southern and eastern Europe. Hair and eye colour showed considerable variability, the earliest sign of red hair showing up in Turkey. Even Copper- and Bronze Age samples ( 113 from 7 to 3 ka) and those from Iron Age Europeans (25 from 3 to 1.7 ka ago) still indicate common retention of dark skin, eyes and hair, although the proportion of lighter pigmentation increased in some regions of Europe. Other analyses of ancient DNA have shown that the Palaeo- and Mesolithic populations of Europe were quickly outnumbered by influx of early farmers, probably from the Anatolian region of modern Turkey, during the Neolithic. The farming lifestyle seems likely to have allowed the numbers of those who practised it to rise beyond the natural environment’s ‘carrying capacity’ for hunter-gatherers. The former inhabitants of Europe may simply have been genetically absorbed within the growing population of farmers. Much the same absorption of earlier groups seems to have happened with the westward migration from the Ukrainian and Russia steppes of the Yamnaya people and culture, culminating in the start of the European Bronze Age that reached western Europe around 2.1 ka, The Yamnaya introduced metal culture, horse-drawn wheeled vehicles and possibly Indo-European language.

So the novel probabilistic approach to ancient DNA by Perretti et al. also casts doubt on the diet-based evolution of light pigmentation at high latitudes. Instead, pulses of large population movements and thus changes in European population genetics probably account for the persistence of abundant evidence for dark pigmentation throughout Europe until historic times. The ‘lightening’ of Europeans’ physiognomy seems to have been vastly more complex than previously believed. Early Europe seems to have been almost bewilderingly diverse, which make a complete mockery of modern chauvinism and racism. The present European genetic ‘melting pot’ is surprisingly similar to that of Europe’s ancient past.

The end-Triassic mass extinction and ocean acidification

Published on July 22, 2025July 28, 2025 by zooks777Leave a comment

Triassic reef limestones in the Dolomites of northern Italy. Credit: © Matteo Volpone

Four out of six mass extinctions that ravaged life on Earth during the last 300 Ma coincided with large igneous events marked by basaltic flood volcanism. But not all such bursts of igneous activity match significant mass extinctions. Moreover, some rapid rises in the rate of extinction are not clearly linked to peaks in igneous activity. Another issue in this context is that ‘kill mechanisms’ are generally speculative rather than based on hard data. Large igneous events inevitably emit very large amounts of gases and dust-sized particulates into the atmosphere. Carbon dioxide, being a greenhouse gas, tends to heat up the global climate, but also dissolves in seawater to lower its pH. Both global warming and more acidic oceans are possible ‘kill mechanisms’. Volcanic emission of sulfur dioxide results in acid rain and thus a decrease in the pH of seawater. But if it is blasted into the stratosphere it combines with oxygen and water vapour to form minute droplets of sulfuric acid. These form long-lived haze, which reflects solar energy beck into space. Such an increased albedo therefore tends to cool the planet and create a so-called ‘volcanic winter’. Dust that reaches the stratosphere reduces penetration of visible light to the surface, again resulting in cooling. But since photosynthetic organisms rely on blue and red light to power their conversion of CO₂ and water vapour to carbohydrates and oxygen, these primary producers at the base of the marine and terrestrial food webs decline. That presents a fourth kill mechanism that may trigger mass extinction on land and in the oceans: starvation.

Palaeontologists have steadily built up a powerful case for occasional mass extinctions since fossils first appear in the stratigraphic record of the Phanerozoic Eon. Their data are simply the numbers of species, genera and families of organisms preserved as fossils in packages of sedimentary strata that represent roughly equal ‘parcels’ of time (~10 Ma). Mass extinctions are now unchallengeable parts of life’s history and evolution. Yet, assigning specific kill mechanisms involved in the damage that they create remains very difficult. There are hypotheses for the cause of each mass extinction, but a dearth of data that can test why they happened. The only global die-off near hard scientific resolution is that at the end of the Cretaceous. The K-Pg (formerly K-T) event has been extensively covered in Earth-logs since 2000. It involved a mixture of global ecological stress from the Deccan large igneous event spread over a few million years of the Late Cretaceous, with the near-instantaneous catastrophe induced by the Chicxulub impact, with a few remaining dots and ticks needed on ‘i’s and ‘t’s. Other possibilities have been raised: gamma-ray bursts from distant supernovae; belches of methane from the sea floor; emissions of hydrogen sulfide gas from seawater itself during ocean anoxia events; sea-level changes etc.

The mass extinction that ended the Triassic (~201 Ma) coincides with evidence for intense volcanism in South and North America, Africa and southern Europe, then at the core of the Pangaea supercontinent. Flood basalts and large igneous intrusions – the Central Atlantic Magmatic Province (CAMP) – began the final break-up of Pangaea. The end-Triassic extinction deleted 34% of marine genera. Marine sediments aged around 201 Ma reveal a massive shift in sulfur and carbon isotopes in the ocean that has been interpreted as a sign of acute anoxia in the world’s oceans, which may have resulted in massive burial of oxygen-starved marine animal life. However, there is no sign of Triassic, carbon-rich deep-water sediments that characterise ocean anoxia events in later times. But it is possible that bacteria that use the reduction of sulfate (SO₄^2-) to sulfide (S^2-) ions as an energy source for them to decay dead organisms, could have produced the sulfur isotope ‘excursion’. That would also have produced massive amounts of highly toxic hydrogen sulfide gas, which would have overwhelmed terrestrial animal life at continental margins. The solution ofH₂S in water would also have acidified the world’s oceans.

Molly Trudgill of the University of St Andrews, Scotland and colleagues from the UK, France, the Netherlands, the US, Norway, Sweden and Ireland set out to test the hypothesis of end-Triassic oceanic acidification (Trudgill, M. and 24 others 2025. Pulses of ocean acidification at the Triassic–Jurassic boundary. Nature Communications, v. 16, article 6471; DOI: 10.1038/s41467-025-61344-6). The team used Triassic fossil oysters from before the extinction time interval. Boron-isotope data from the shells are a means of estimating variations in the pH of seawater. Before the extinction event the average pH in Triassic seawater was about the same as today, at 8.2 or slightly alkaline. By 201 Ma the pH had shifted towards acidic conditions by at least 0.3: the biggest detected in the Phanerozoic record. One of the most dramatic changes in Triassic marine fauna was the disappearance of reef limestones made by the recently evolved modern corals on a vast scale in the earlier Triassic; a so-called ‘reef gap’ in the geological record. That suggests a possible analogue to the waning of today’s coral reefs that is thought to be a result of increased dissolution of CO₂ in seawater and acidification, related to global greenhouse warming. Using the fossil oysters, Trudgill et al. also sought a carbon-isotope ‘fingerprint’ for the source of elevated CO₂, finding that it mainly derived from the mantle, and was probably emitted by CAMP volcanism. So their discussion centres mainly on end-Triassic ocean acidification as an analogy for current climate change driven by CO₂ largely emitted by anthropogenic burning of fossil fuels. Nowhere in their paper do they mention any role for acidification by hydrogen sulfide emitted by massive anoxia on the Triassic ocean floor, which hit the scientific headlines in 2020 (see earlier link).

Sagduction of greenstone belts and formation of Archaean continental crust

Published on July 11, 2025 by zooks777Leave a comment

Simplified geological map of the Archaean Yilgarn Craton in Western Australia. Credit: Geological Survey of Western Australia

Every ancient craton seen from space shows patterns that are unique to Archaean continental crust: elongated, ‘canoe-shaped’ greenstone belts enveloped by granitic gneisses, both of which are punctured by domes of younger, less deformed granites. The Yilgarn Craton of Western Australia is a typical granite-greenstone terrain. Greenstone belts contain lavas of ultramafic, basaltic and andesitic compositions, which in undeformed settings show the typical pillow structures formed by submarine volcanic extrusion. There are also layered mafic to ultramafic complexes, formed by fractional crystallisation, minor sedimentary sequences and occasionally more felsic lavas and ashes. The enveloping grey gneisses are dominantly highly deformed tonalite-trondhjemite-granodiorite (TTG) composition that suggest that they formed from large volumes of sodium-rich, silicic magmas, probably generated at depth by partial melting of hydrated basaltic rocks.

The heat producing radioactive isotopes of potassium, uranium and thorium in both the Archaean mantle and crust would have been more abundant before 2.5 Ga ago, because they decay over time. Consequently the Earth’s interior would have then generated more heat than now, gradually to escape by thermal conduction towards the cooler surface. The presence of pillow lavas and detrital sediments in greenstone belts indicate that surface temperatures during the Archaean Eon were below the boiling point of water; in fact probably much the same as in the tropics at present. Indeed there is evidence that Earth was then a water world. It may even have been so during the Hadean, as revealed by the oxygen-isotope data in 4.4 Ga zircon grains. The broad conclusion from such findings is that the Archaean geothermal gradient was much steeper; there would have been a greater temperature increase with depth than now and new crust would have cooled more slowly. Subduction of cool lithosphere would have been less likely than in later times, especially as higher mantle heat production would have generated new crust more quickly. Another likely possibility is that far more heat would have been moved by convection: there would have been more mantle-penetrating plumes and they would have been larger. Large mantle plumes of the Phanerozoic have generated vast ocean floor plateaus, such as the Kerguelen and Ontong Java Plateau.

A group of geoscience researchers at The University of Hong Kong and international colleagues recently completed a geological and geochemical study of the North China Craton, analysing their data in the light of recently emerging views on Archaean processes (Dingyi Zhao et al, A two-stage mantle plume-sagduction origin of Archean continental crust revealed by water and oxygen isotopes of TTGs, Science Advances, v. 11, article eadr9513 ; DOI: 10.1126/sciadv.adr9513).They found compelling evidence that ~2.5 Ga-old Neoarchaean TTG gneisses in the North China granite-greenstone terrain formed by partial melting of an earlier mafic-ultramafic greenstone crust with high water content. They consider this to support a two-stage model for the generation of the North China Craton’s crust above a vast mantle plume. The first stage at around 2.7 Ga was the arrival of the plume at the base of the lithosphere, which partially melted as a result of the decompression of the rising ultramafic plume. The resulting mafic magma created an oceanic plateau partly by underplating the older lithosphere, intruding it and erupting onto the older ocean floor. This created the precursors of the craton’s greenstones, the upper part of which interacted directly with seawater to become hydrothermally altered. They underwent minor partial melting to produce small TTG intrusions. A second plume arriving at ~2.5 Ga resulted in sinking of the greenstones under their own weight to mix or ‘hybridise’ with the re-heated lower crust. This caused the greenstones substantially to partially melt and so generate voluminous TTG magmas that rose as the greenstones subsided. . It seems likely that this dynamic, hot environment deformed the TTGs as they rose to create the grey gneisses so typical of Archaean granite-greenstone terranes. [Note: The key evidence for Dingyi Zhao et al.’s conclusions is that the two TTG pulses yielded the 2.7 and 2.5 Ga ages, and show significantly different oxygen isotope data (δ¹⁸O)].

Two stages of TTG gneiss formation in the North China Craton and the sinking (sagduction) of greenstone belts in the second phase. Credit: Dingyi Zhao et al., Fig 4)

Such a petrogenetic scenario, termed sagduction by Dingyi Zhao and colleagues, also helps explain the unique keel-like nature of greenstone belts, and abundant evidence of vertical tectonics in many Archaean terrains (see: Vertical tectonics and formation of Archaean crust; January 2002), Their model is not entirely new, but is better supported by data than earlier, more speculative ideas. That such processes have been recognised in the Neoarchaean – the North China Craton is one of the youngest granite-greenstone terrains – may well apply to far older Archaean continental crust generation. It is perhaps the last of a series of such events that began in the Hadean, as summarised in the previous Earth-logs post.

The world’s oldest crust in the Nuvvuagittuq Greenstone Belt, Quebec

Published on June 28, 2025 by zooks7772 Comments

Since 1999, the rocks generally acknowledged to be the oldest on Earth were part of the Acasta gneisses in the Slave Craton in Canada’s Northwest Territories; specifically the Idiwhaa tonalitic gneisses. Zircons extracted from that unit yielded an age of 4.02 billion years (Ga) using U-Pb radimetric dating, revealing the time of their crystallisation from granitic magma. But nine years later some metabasaltic rocks from the tiny (20 km²) Nuvvuagittuq Greenstone Belt on the eastern shore of Hudson Bay were dated using the Sm-Nd method at almost 4.3 Ga (see: At last, 4.0 Ga barrier broken; November 2008). Taken at face value the metabasaltic rocks seemed to be well within the Hadean Eon (4.6 to 4.0 Ga) and could thus represent primary crust of that antiquity. However, U-Pb dating of zircons from thin sodium-rich granitic rocks (trondhjemites) that intrude them yielded ages no older than about 3.8 Ga. Similar ages emerged from zircons found in metasediments interleaved in the dominant mafic unit. Discrepancies between the two completely different dating methods resulted in the Hadean antiquity of the mafic rocks having been disputed since 2008. It was possible that the Sm-Nd results from the metabasalts may have resulted from the original mafic magmas having inherited a Hadean Sm-Nd isotopic ‘signature’ from their mantle source. That is, they may have been contaminated and could have formed in the early Archaean.

Glacially smoothed outcrops near Inukjuak, Quebec that reveals rocks of the Nuvvuagittuq Greenstone Belt. Credit: Jonathan O’Neil, University of Ottawa

Jonathan O’Neil, now at Ottawa University in Canada, led the first isotopic investigation of the Nuvvuagittuq Greenstone Belt and has engaged in research there ever since. Further field and laboratory studies revealed that the previously dated mafic rocks had been intruded by large, chemically differentiated gabbro sills. A team of geochemists from the University of Ottawa and Carleton University, including O’Neil, has now published isotopic evidence from the intrusions that suggests a Hadean age for their parent magma (C. Sole et al. 2025. Evidence for Hadean mafic intrusions in the Nuvvuagittuq Greenstone Belt, Canada. Science, v. 388, p. 1431-1435. DOI: 10.1126/science.ads8461). The authors used the decay schemes of two radioactive samarium isotopes ¹⁴⁷Sm and ¹⁴⁶Sm; a significant advance in radiometric dating. The first decays to ¹⁴³Nd with a half-life of about 10¹¹ years, the second to ¹⁴²Nd with a much shorter half life of about 10⁸ years. Due to its more rapid decay, in geological terms,¹⁴⁶Sm is now much rarer than ¹⁴⁷Sm. Consequently, using the short-lived ¹⁴⁶Sm-¹⁴²Nd decay system is technically more difficult than that of the ¹⁴⁷Sm-¹⁴³Nd system. But the team managed to get good results from both the ‘fast’ and the ‘slow’ decay schemes. They tally nicely, yielding ages of 4157 and 4196 Ma. The gabbros provide a minimum age for the metabasalts that they cut through. The original 4.3 Ga Sm-Nd date for the metabasalts is thus plausible. Sole and colleagues consider the dominant metabasaltic rocks to have formed a primary crust in late Hadean times that was invaded by later mantle-derived mafic magma about 100 Ma later. The granitic rocks that constitute about one third of the Nuvvuagittuq terrain seem to have been generated by partial melting more than 300 Ma later still, during the Palaeoarchaean.

Perhaps similar techniques will now be deployed in granite-greenstone terrains in other cratons. Many of the older ones, generally designated as Palaeoarchaean in age, also contain abundant metamorphosed mafic and ultramafic igneous rocks. Perhaps their origin was akin to those of Nuvvuagittuq; i.e. more Hadean crust may await unmasking. Meanwhile, there seems to be more to discover from Nuvvuagittuq. For instance, some of the rocks suggested to be metasediments interleaved in the metabasalts show intricate banding that resembles products of bacterial mat accumulation in younger terrains. Signs of Hadean life?

Since the first reliable radiometric dating of Archaean rocks in 1971, there has been an element of competition to date the oldest rocks on Earth: to push history back towards the initial formation of the Earth. It is one of the most disputatious branches of Earth history. Rivalry may play a significant part in driving the science, as well as the development of novel dating techniques and the continuing discovery of clearly old relationships using ‘old-fashioned’ relative dating, such as signs of intrusion, unconformities etcetera. But in some cases there is a darker side: the potential for profit. Recently, samples from Nuvvuagittuq appeared for sale on the Internet, priced at $10,000. They may have been collected under the guise of supplying museums by a group that shipped-in mechanical excavators in 2016. Unsurprisingly this angered the local Innuit community of Inukjuak. They were also worried about bona fide collection for scientific research that had left parts of the small, once pristine area somewhat battered, including cultural features such as an inukshuk navigational monument. Their fury at commercial exploitation of their homeland resulted in the community council closing the area to collecting in 2024. I emphasise that this violation of basic geological ethics was by commercial rock collectors and dealers, not academic geologists. The local people are now considering careful issue of research permits so that important research can continue. But further rock collecting may remain banned.

See also: New Research Verifies Northern Canada Hosts Earth’s Oldest Rocks. Scienmag, 26 June 2025; Gramling, C. 2025. Earth’s oldest rocks may be at least 4.16 billion years old. ScienceNews.

PS With many thanks to ‘Piso Mojado’ for alerting me to this paper

Chinese skull confirmed as Denisovan

Published on June 19, 2025 by zooks777Leave a comment

For over a century Chinese scientists have been puzzling over ancient human skulls that show pronounced brow ridges. Some assigned them to Homo, others to species that they believe were unique to China. A widely held view in China was that people now living there evolved directly from them, adhering to the ‘Multiregional Evolution’ hypothesis as opposed to that of ‘Out of Africa’. However, the issue might now have been resolved. In the last few years palaeoanthropologists have begun to suspect that these fossilised crania may have been Denisovans, but none had been subject to genetic and proteomic analysis. The few from Siberia and Tibet that initially proved the existence of Denisovans were very small: just a finger bone and teeth. Out of the blue, teeth in a robust hominin mandible dredged from the Penghu Channel between Taiwan and China yielded protein sequences that matched proteomic data from Denisovan fossils in Denisova Cave and Baishiya Cave in Tibet, suggesting that Denisovans were big and roamed widely in East Asia. In 2021 a near-complete robust cranium came to light that had been found in the 1930s near Harbin in China and hidden – at the time the area was under Japanese military occupation. It emerged only when its finder revealed its location in 2018, shortly before his death. It was provisionally called Homo longi or ‘Dragon Man’. Qiaomei Fu of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing and her colleagues have made a comprehensive study of the fossil.

The cranium found near Harbin, China belonged to a Denisovan. Credit: Hebei Geo University

It is at least 146 ka old, probably too young to have been H. erectus, but predates the earliest anatomically modern humans to have reached East Asia from Africa (~60 ka ago). The Chinese scientists have developed protein- and DNA extraction techniques akin to those pioneered at the Max Planck Institute for Evolutionary Anthropology in Leipzig. It proved impossible to extract sufficient ancient nuclear DNA from the cranium bone for definitive genomic data to be extracted, but dental plaque (calculus) adhering around the only surviving molar in the upper jaw did yield mitochondrial DNA. The mtDNA matched that found in Siberian Denisovan remains (Qiaomei Fu et al. 2025. Denisovan mitochondrial DNA from dental calculus of the >146,000-year-old Harbin cranium. Cell, v. 188, p. 1–8; DOI: 10.1016/j.cell.2025.05.040). The bone did yield 92 proteins and 122 single amino acid polymorphisms, as well as more than 20 thousand peptides (Qiaomei Fu and 8 others 2025. The proteome of the late Middle Pleistocene Harbin individual. Science, v. 388: DOI: 10.1126/science.adu9677). Again, these established a molecular link with the already known Denisovans, specifically with one of the Denisova Cave specimens. Without the painstaking research of the Chinese team, Denisovans would have been merely a genome and a proteome without much sign of a body! From the massive skull it is clear that they were indeed big people with brains much the same size as those of living people. Estimates based on the Harbin cranium suggest an individual weighing around 100 kg (220 lb or ~15 stone): a real heavyweight or rugby prop!

The work of Qiaomei Fu and her colleagues, plus the earlier, more limited studies by Tsutaya et al., opens a new phase in palaeoanthropology. Denisovans now have a genome and well-preserved parts of an entire head, which may allow the plethora of ancient skulls from China to be anatomically assigned to the species. Moreover, by extracting DNA from dental plaque for the first time they have opened a new route to obtaining genomic material: dental calculus is very much tougher and less porous than bone.

See also: Curry, A. ‘Dragon Man’ skull belongs to mysterious human relative. 2025. Science, v. 388; DOI: 10.1126/science.z8sb68w. Smith K. 2025. We’ve had a Denisovan skull since the 1930s – only nobody knew. Ars Technica, 18 June 2025. Marshall, M. 2025. We finally know what the face of a Denisovan looked like. New Scientist 18 June 2025.

Detecting oxygenic photosynthesis in the Archaean Earth System

Published on June 9, 2025 by zooks777Leave a comment

For life on Earth, one of the most fundamental shifts in ecosystems was the Great Oxygenation Event 2.5 to 2.3 billion years (Ga) ago. The first evidence for its occurrence was from the sedimentary record, particularly ancient soils (palaeosols) that mark exposure of the continental surface above sea level and rock weathering. Palaeosols older than 2.4 Ga have low iron contents that suggest iron was soluble in surface waters, i.e. in its reduced bivalent form Fe²⁺. Sediments formed by flowing water also contain rounded grains of minerals that in today’s oxygen-rich environments are soon broken down and dissolved through oxidising reactions, for instance pyrite (FeS₂) and uraninite (UO₂). After 2.4 Ga palaeosols are reddish to yellowish brown in colour and contain insoluble oxides and hydroxides of Fe³⁺ principally hematite (Fe₂O₃) and goethite (FeO.OH). After this time sediments deposited by wind action and rivers are similar in colour: so-called ‘redbeds’. Following the GOE the atmosphere initially contained only traces of free oxygen, but sufficient to make the surface environment oxidising. In fact such an atmosphere defies Le Chatelier’s Principle: free oxygen should react rapidly with the rest of the environment through oxidation. That it doesn’t shows that it is continually generated as a result of oxygenic photosynthesis. The CO₂ + H₂O = carbohydrate + oxygen equilibrium does not reach a balance because of continual burial of dead organic material.

Free oxygen is a prerequisite for all multicelled eukaryotes, and it is probably no coincidence that fossils of the earliest known ones occur in sediments in Gabon dated at 2.1 Ga: 300 Ma after the Great Oxygenation Event. However, the GOE relates to surface environments of that time. From 2.8 Ga – in the Mesoarchaean Era – to the late Palaeoproterozoic around 1.9 Ga, vast quantities of Fe³⁺ were locked in iron oxide-rich banded iron formations (BIFs): roughly 10⁵ billion tons in the richest deposits alone (see: Banded iron formations (BIFs) reviewed; December 2017). Indeed, similar ironstones occur in Archaean sedimentary sequences as far back as 3.7 Ga, albeit in uneconomic amounts. Paradoxically, enormous amounts of oxygen must have been generated by marine photosynthesis to oxidise Fe²⁺ dissolved in the early oceans by hydrothermal alteration of basalt lava upwelling from the Archaean mantle. But none of that free oxygen made it into the atmosphere. Almost as soon as it was released it oxidised dissolved Fe²⁺ to be dumped as iron oxide on the ocean floor. Before the GOE that aspect of geochemistry did obey Le Chatelier!

The only likely means of generating oxygen on such a gargantuan scale from the earliest Archaean onwards is through teeming prokaryote organisms capable of oxygenic photosynthesis. Because modern cyanobacteria do that, the burden of the BIFs has fallen on them. One reason for that hypothesis stems from cyanobacteria in a variety of modern environments building dome-shaped bacterial mats. Their forms closely resemble those of Archaean stromatolites found as far back as 3.7 Ga. But these are merely peculiar carbonate bodies that could have been produced by bacterial mats which deploy a wide variety of metabolic chemistry. Laureline Patry of the Université de Bretagne Occidentale, Plouzané, France, and colleagues from France, the US, Canada and the UK have developed a novel way of addressing the opaque mechanism of Archaean oxygen production (Patry, L.A. and 12 others. Dating the evolution of oxygenic photosynthesis using La-Ce geochronology. Nature, v. 642, p. 99-104; DOI: 10.1038/s41586-025-09009-8).

They turned to the basic geochemistry of rare earth elements (REE) in Archaean stromatolitic limestones from the Superior Craton of northern Canada. Of the 17 REEs only cerium (Ce) is capable of being oxidised in the presence of oxygen. As a result Ce can be depleted relative to its neighbouring REEs in the Periodic Table, as it is in many Phanerozoic limestones. Five samples of the limestones show consistent depletion of Ce relative to all other REE. It is also possible to date when such fractionation occurred using ¹³⁸La– ¹³⁸Ce geochronology. The samples were dated at 2.87 to 2.78 Ga (Mesoarchaean), making them the oldest limestones that show Ce anomalies and thus oxygenated seawater in which the microbial mats thrived. But that is only 300 Ma earlier than the start of the GOE. Stromatolites are abundant in the Archaean record as far back as 3.4 Ga, so it should be possible to chart the link between microbial carbonate mats and oxygenated seawater to a billion years before the GOE, although that does not tell us about the kind of microbes that were making stromatolites.

See also: Tracing oxygenic photosynthesis via La-Ce geochronology. Bioengineer.org, 29 May 2025; Allen, J.F. 2016. A proposal for formation of Archaean stromatolites before the advent of oxygenic photosynthesis. Frontiers in Microbiology, v. 7; DOI: 10.3389/fmicb.2016.01784.

Arsenic: an agent of evolutionary change?

Published on June 2, 2025 by zooks777Leave a comment

The molecules that make up all living matter are almost entirely (~98 %) made from the elements Carbon, Hydrogen, Oxygen, Nitrogen and Phosphorus (CHONP) in order of their biological importance. All have low atomic numbers, respectively 6^th, 1^st, 8^th, 7^th and 15^thin the Periodic Table. Of the 98 elements found in nature, about 7 occur only because they form in the decay schemes of radioactive isotopes. Only the first 83 (up to Bismuth) are likely to be around ‘for ever’; the fifteen heavier than that are made up exclusively of unstable isotopes that will eventually disappear, albeit billions of years from now. There are other oddities that mean that the 92 widely accepted to be naturally occurring is not strictly correct. That CHONP are so biologically important stems partly from their abundances in the inorganic world and also because of the ease with which they chemically combine together. But they are not the only ones that are essential.

About 20 to 25% of the other elements are also literally vital, even though many are rare. Most of the rest are inessential except in vanishingly small amounts that do no damage, and may or may not be beneficial. However some are highly toxic. Any element can produce negative biological outcomes if above certain levels. Likewise, deficiencies can result in ill thrift and event death. For the majority of elements, biologists have established concentrations that define deficiency and toxic excess. The World Health Organisation has charted the maximum safe levels of elements in drinking water in milligrams per litre. In this regard, the lowest safe level is for thallium (Tl) and mercury (Hg) at 0.002 mg l^-1.Other highly toxic elements are cadmium (Cd) (0.003 mg l^-1), then arsenic (As) and lead (Pb) (0.01 mg l^-1) that ‘everyone knows’ are elements to avoid like the plague. In nature lead is very rarely at levels that are unsafe because it is insoluble, but arsenic is soluble under reducing conditions and is currently responsible for a pandemic of related ailments, especially in the Gangetic plains of India and Bangladesh and similar environments worldwide.

Biological evolution has been influenced since life appeared by the availability, generally in water, of both essential and toxic elements. In 2020 Earth-logs summarised a paper about modern oxygen-free springs in Chile in which photosynthetic purple sulfur bacteria form thick microbial mats. The springs contain levels of arsenic that vary from high in winter to low in summer. This phenomenon can only be explained by some process that removes arsenic from solution in summer but not in winter. The purple-bacteria’s photosynthesis uses electrons donated by sulfur, iron-2 and hydrogen – the spring water is highly reducing so they thrive in it. In such a simple environment this suggested a reasonable explanation: the bacteria use arsenic too. In fact they contain a gene (aio) that encodes for such an eventuality. The authors suggested that purple sulfur bacteria may well have evolved before the Great Oxygenation Event (GOE). They reasoned that in an oxygen-free world arsenic, as well as Fe²⁺ would be readily available in water that was in a reducing state, whereas oxidising conditions after the GOE would suppress both: iron-2 would be precipitated as insoluble iron-3 oxides that in turn efficiently absorb arsenic (see: Arsenic hazard on a global scale, May 2020).

Colour photograph and CT scans of Palaeoproterozoic discoidal fossils from the Francevillian Series in Gabon. (Credit: El Albani et al. 2010; Fig. 4).

A group of geoscientists from France, the UK, Switzerland and Austria have investigated the paradox of probably high arsenic levels before the GOE and the origin and evolution of life during the Archaean (El Khoury et al. 2025. A battle against arsenic toxicity by Earth’s earliest complex life forms. Nature Communications, v. 16, article 4388; DOI: 10.1038/s41467-025-59760-9). Note that the main, direct evidence for Archaean life are fossilized microbial mats known as stromatolites, some palaeobiologists reckoning they were formed by oxygenic photosynthesising cyanobacteria others favouring the purple sulfur bacteria (above). The purple sulfur bacteria in Chile and other living prokaryotes that tolerate and even use arsenic in their metabolism clearly evolved that potential plus necessary chemical defence mechanisms, probably when arsenic was more available in the anoxic period before the GOE. Anna El Khoury and her colleagues sought to establish whether or not eukaryotes evolved similar defences by investigating the earliest-known examples; the 2.1 Ma old Francevillian biota of Gabon that post-dates the GOE. They are found in black shales, look like tiny fried eggs and are associated with clear signs of burrowing. The shales contain steranes that are breakdown products of steroids, which are unique to eukaryotes.

The fossils have been preserved by precipitation of pyrite (Fe₂S) granules under highly reducing conditions. Curiously, the cores of the pyrite granules in the fossils are rich in arsenic, yet pyrite grains in the host sediments have much lower As concentrations. The latter suggest that seawater 2.1 Ma ago held little dissolved arsenic as a result of its containing oxygen. The authors interpret the apparently biogenic pyrite’s arsenic cores as evidence of the organism having sequestered As into specialized compartments in their bodies: their ancestors must have evolved this efficient means of coping with significant arsenic stress before the GOE. It served them well in the highly reducing conditions of black shale sedimentation. Seemingly, some modern eukaryotes retain an analogue of a prokaryote As detoxification gene.

How the earliest continental crust may have formed

Published on May 28, 2025 by zooks7771 Comment

Detrital zircon grains extracted from sandstones deposited ~3 billion year (Ga) ago in Western Australia yield the ages at which these grains crystallised. The oldest formed at about 4.4 Ga; only 150 Ma after the origin of the Earth (4.55 Ga). Various lines of evidence suggest that they originally crystallized from magmas with roughly andesitic compositions, which some geochemists suggest to have formed the first continental crust (see: Zircons and early continents no longer to be sneezed at; February 2006). So far, no actual rocks of that age and composition have come to light. The oldest of these zircon grains also contain anomalously high levels of ¹⁸O, a sign that water played a role in the formation of these silicic magmas. Modern andesitic magmas – ultimately the source of most continental crust – typically form above steeply-dipping subduction zones where fluids expelled from descending oceanic crust encourage partial melting of the overriding lithospheric mantle. Higher radiogenic heat production in the Hadean and the early Archaean would probably have ensured that the increased density of later oceanic lithosphere needed for steep subduction could not have been achieved. If subduction occurred at all, it would have been at a shallow angle and unable to exert the slab-pull force that perpetuated plate tectonics in later times (see: Formation of continents without subduction, March, 2017).

Landsat image mosaic of the Palaeoarchaean granite-greenstone terrain of the Pilbara Craton, Western Australia. Granite bodies show as pale blobs, the volcanic and sedimentary greenstone belts in shades of grey.

Geoscientists have been trying to resolve this paradox for quite a while. Now a group from Australia, Germany and Austria have made what seems to be an important advance (Hartnady, M. I. H and 8 others 2025. Incipient continent formation by shallow melting of an altered mafic protocrust. Nature Communications, v. 16, article 4557; DOI: 10.1038/s41467-025-59075-9). It emerged from their geochemical studies of rocks in the Pilbara Craton of Western Australia that are about a billion years younger than the aforementioned ancient zircon grains. These are high-grade Palaeoarchaean metamorphic rocks known as migmatites that lie beneath lower-grade ‘granite-greenstone’ terrains that dominate the Craton, which Proterozoic deformation has forced to the surface. Their bulk composition is that of basalt which has been converted to amphibolite by high temperature, low pressure metamorphism (680 to 730°C at a depth of about 30 km). These metabasic rocks are laced with irregular streaks and patches of pale coloured rock made up mainly of sodium-rich feldspar and quartz, some of which cut across the foliation of the amphibolites. The authors interpret these as products of partial melting during metamorphism, and they show signs of having crystallised from a water-rich magma; i.e. their parental basaltic crust had been hydrothermally altered, probably by seawater soon after it formed. The composition of the melt rocks is that of trondhjemite, one of the most common types of granite found in Archaean continental crust. Interestingly, small amounts of trondhjemite are found in modern oceanic crust and ophiolites.

A typical migmatite from Antarctica showing dark amphibolites laced with quartzofeldspathic products of partial melting. Credit: Lunar and Planetary Laboratory, University of Arizona

The authors radiometrically dated zircon and titanite (CaTiSiO₅) – otherwise known as sphene – in the trondhjemites, to give an age of 3565 Ma. The metamorphism and partial melting took place around 30 Ma before the overlying granite-greenstone assemblages formed. They regard the amphibolites as the Palaeoarchaean equivalent of basaltic oceanic crust. Under the higher heat production of the time such primary crust would probably have approached the thickness of that at modern oceanic plateaux, such as Iceland and Ontong-Java, that formed above large mantle plumes. Michael Hartnady and colleagues surmise that this intracrustal partial melting formed a nucleus on which the Pilbara granite-greenstone terrain formed as the oldest substantial component of the Australian continent. The same nucleation may have occurred during the formation of similar early Archaean terrains that form the cores of most cratons that occur in all modern continents.

Impact debris in Neoproterozoic sediments of Scotland and biological evolution?

Published on April 30, 2025April 30, 2025 by zooks777Leave a comment

False-colour electron microscope image of a shocked grain of zircon recovered from the Stac Fada Member. The red and pink material is a high-pressure polymorph of zircon, arranged in shock lamellae. Zircon is rendered in cyan, some of which is in granulated form. Credit: Kirkland et al. 2025, Fig 2C

Judging by its content of shards and spherules made of murky green glass, one of the lowest units in the Torridonian continental sediments of NW Scotland had long been regarded as simply red sandstone that contained volcanic debris. This Stac Fada Member was thus celebrated as the only sign of a volcanic contribution to a vast thickness (up to 2.5 km) of Neoproterozoic lake and fluviatile sediments. Current flow indicators suggested that the Torridonian was laid down by large alluvial fans derived by erosion of much older crystalline basement far to what is today the west. That is, the Archaean core of the ancient continent of Laurentia, now the other side of the North Atlantic. In 2002 more sophisticated sedimentological and geochemical analysis of the Stac Fada Member revealed a surprise: it contains anomalously elevated platinum-group elements, quartz grains that show signs of shock and otherworldly chromium isotope concentrations. The 10 m thick bed is made from ejecta, perhaps from a nearby impact crater to the WNW concluded from brittle fractures that may have been produced by the impact. Some idea of its age was suggested by Ar-Ar dating of feldspar crystals (~1200 Ma) believed to have formed authigenically in the hot debris. Being the only decent impactite known in Britain, it continues to attract attention.

A group of geoscientists from Western Australia, NASA and the UK, independent of the original discoverers, have now added new insights ( Kirkland, C.L. and 12 others 2025. A one-billion-year old Scottish meteorite impact. Geology, v. 53, early online publication; DOI: 10.1130/G53121.1). They dated shocked zircon grains using U-Pb analyses at 990 ± 22 Ma; some 200 Ma younger than the previously dated, authigenic feldspars. Detrital feldspar grains in the Stac Fada Member yield Rb-Sr radiometric ages of 1735 and 1675, that are compatible with Palaeoproterozoic granites in the underlying Lewisian Gneiss Complex.

Photomicrograph of Bicellum brazieiri: scale bar = 10μm; arrows point to dark spots that may be cell nuclei (credit: Charles Wellman, Sheffield University)

In a separate publication (Kirkland, C.L et al 2025. 1 billion years ago, a meteorite struck Scotland and influenced life on Earth. The Conversation, 29 April 2025) three of the authors take things a little further, as their title suggests. In this Conversation piece they ponder, perhaps unwarily, on the spatial and temporal association of the indubitable impact with remarkably well-preserved spherical fossils found in Torridonian lake-bed sediments (Bicellum brasieri, reported in Earth-logs in May 2021), which are the earliest-known holozoan animal ancestors. The Torridonian phosphatic concretions in which these important fossils were found at a different locality are roughly 40 Ma younger than the Stac Fada impactite. The authors of the Conversation article appeal to the residual thermal effect of the impact as a possible driver for the appearance of these holozoan organisms. Whether a residual thermal anomaly would last long enough for them to evolve to this biological status would depend on the magnitude of the impact, of which we know nothing. Eukaryote fossils are known from at least 650 Ma older sedimentary rocks in northern China and perhaps as far back as 2.2 Ga in a soil that formed in the Palaeoproterozoic of South Africa. Both the Torridonian organism and impactite were found in a small area of fascinating geology that has been studied continuously in minute detail since Victorian times, and visited by most living British geologists during their undergraduate days. Ideas will change as curiosity draws geologists and palaeobiologists to less-well studied sites of Proterozoic antiquity, quite possibly in northern China.

A fully revised edition of Steve Drury’s book Stepping Stones: The Making of Our Home World can now be downloaded as a free eBook

A sign of life on another planet? Should we be excited?

Published on April 19, 2025April 19, 2025 by zooks777Leave a comment

Judging by the coverage in the media, there is huge excitement about a possible sign of life on a very distant planet. It emerged from a Letter to The Astrophysical Journal posted by a British-US team of astronomers led by Nikku Madhusudhan that was publicised by the Cambridge University Press Office (Madhusudhan, N.et al. 2025. New Constraints on DMS and DMDS in the Atmosphere of K2-18 b from JWST MIRI. The Astrophysical Journal, v. 983, article adc1c8; DOI: 10.3847/2041-8213/adc1c8). K2-18 b is a planet a bit smaller than Neptune that orbits a red dwarf star (K2-18) about 124 light years away. The planet was discovered by NASA’s now-defunct Kepler space telescope tasked with the search for planets orbiting other stars. An infrared spectrometer on the Hubble Space Telescope revealed in 2019 that the atmosphere of K2-18 b contained water vapour, making the planet a target for further study as it may possess oceans. The more sophisticated James Webb Space Telescope IR spectrometer was trained on it a year later to reveal methane and CO₂: yet more reason to investigate more deeply, for water and carbon compounds imply both habitability and the potential for life forms being there.

The latest results suggest that that the atmosphere of K2-18 b may contain simple carbon-sulfur gases: dimethyl sulfide ((CH₃)₂S) and dimethyl disulfide (CH₃SSCH₃). Bingo! for exobiologists, because on Earth both DMS and DMDS are only produced by algae and bacteria. Indeed they are responsible for the odour of the seaside. They became prominent in 1987 when biogeochemist James Lovelock fitted them into his Gaia Hypothesis. He recognised that they encourage cloud formation and thus increase Earth’s reflectivity (albedo) and also yield sulfuric acid aerosols in the stratosphere when they oxidise: that too increases albedo. DMS generates a cooling feedback loop to counter the warming feedback of greenhouse emissions. That is an idea of planetary self-regulation not much mentioned nowadays. Such gases were proposed by Carl Sagan as unique molecular indicators that could be used to search for extraterrestrial life.

The coma of Comet Churyumov-Gerasimenko yielded both dimethyl sulfide and amino acids to the mass spectrometer carried by ESA’s Rosetta. Credit: ESA.

The discovery of possible DMS and DMDS in K2-18 b’s atmosphere is, of course, currently under intense scientific scrutiny. For a start, the statistics inherent in Madhusudhan et al.’s methodology (3σ or 99.7% probability) fall short of the ‘gold standard’ for discoveries in physics (5σ or 99.99999% probability). Moreover, there’s also a chance that exotic, inorganic chemical processes could also create the gases, such as lightning in an atmosphere containing C, H and S. But this is not the first time that DMS has been discovered in an extraterrestrial body. Comets, having formed in the infancy of the Solar System much further from the Sun than any planets, are unlikely to be ‘teeming with life’. The European Space Agency’s Rosetta spacecraft chased comet 67P/Churyumov-Gerasimenko for 2 years, directly sampling dust and gas that it shed while moving closer to the Sun. A single day’s data from Rosetta’s mass spectrometer showed up DMS, and also amino acids. Both could have formed in comets or interstellar dust clouds by chemistry driven by radiation, possibly to contaminate planetary atmospheres. Almost certainly, further remote sensing of K2-18 b will end up with five-sigma precision and some will say, ‘Yes, there is life beyond Earth!’ and celebrate wildly. But that does not constitute proof, even by the ‘weight of evidence’ criterion of some judiciaries. To me such a conclusion would be unseemly romanticism. Yet such is the vastness of the material universe and the sheer abundance of the elements C H O N and P that make up most living matter that life elsewhere, indeed everywhere, (but not life as we know it) is a near certainty. The issue of intelligent lifeforms ‘out there’ is, however, somewhat less likely to be resolved . . .

Middle Palaeolithic Neanderthals and Denisovans of East Asia

Published on April 14, 2025 by zooks777Leave a comment

During the Middle Palaeolithic (250 to 30 ka) anatomically modern humans (AMH) and Neanderthals were engaged in new technological developments in Europe and Africa as well as in migration and social interaction. This is reflected in the tools that they left at occupation sites and the fact that most living non-Africans carry Neanderthal DNA. One of the major cultural developments was a novel means of manufacturing stone implements. It developed from the Levallois technique that involved knapping sharp-edged flakes of hard rock from larger blocks or cores. A type of tool first found at a Neanderthal site near La Quina in France is a thick flake of stone with a broad, sharp edge that shows evidence of having been resharpened many times. Most other flake tools seem to have been ‘one-offs’ that were discarded after brief usage. The Quina version was not only durable but seems to have been multipurpose. Analysis of wear patterns on the sharpened edges suggest that they were deployed in carving wood and bone, removing fat and hair from animal hides, and butchery. Such scrapers have been found over a wide area of Europe, the Middle East and NE Asia mostly at Neanderthal sites, including the famous Denisova Cave of southern Siberia that yielded the first Denisovan DNA as well as that of Neanderthals.

Making a typical Quina scraper and related tools. The toolmaker would flake pieces of stone off the core and then carefully shape the Quina scraper. (Image credit: Pei-Yuan Xiao)

Until now, the early humans of East Asia were thought not to have proceeded beyond more rudimentary tools during the Middle Palaeolithic: in fact that archaeological designation hasn’t been applied there. Recent excavations at Longtan Cave in south-west China have forced a complete revision of that view (Ruan, Q.-J., et al. 2025. Quina lithic technology indicates diverse Late Pleistocene human dynamics in East Asia. Proceedings of the National Academy of Sciences, v. 122, article e2418029122; DOI: 10.1073/pnas.2418029122). The Longtan site has yielded more than fifty scrapers and the cores from which they had been struck that clearly suggest the Quina technology had been used there. They occur in cave sediments dated at between 60 and 50 ka. As yet, no human remains have been found in the same level at Longtan, although deeper levels dated at 412 ka have yielded hominin crania, mandibular fragments, and teeth, that have been suggested to be Homo erectus.

Quina type tools in East Asia may previously have been overlooked at other hominin sites in China: re-examination of archived tool collections may show they are in fact widespread. The technology could have been brought in by migrating Neanderthals, or maybe it was invented independently by local East Asian hominins. Because most living people in China carry Denisovan DNA in the genomes so perhaps that group developed the technique before interbreeding with AMH immigrants from the west. Indeed there is no reason to discard the notion that early AMH may have imported the Quina style. A lot of work lies ahead to understand this currently unique culture at Longtan Cave. However, interpretation of another discovery published shortly after that from Longtan has spectacularly ‘stolen the thunder’ of the Qina tools, and it was made in Taiwan …

Right (top) and downward (lower) views of the partial Penghu mandible. Credit: Yousuke Kaifu University of Tokyo, Japan and Chun-Hsiang Chang Tunghai University, Taichung, from Tsutaya *et al*. Fig. 1 (inset)Taiwan.

About 10 years ago, Taiwanese fishers trawling in the Penghu Channel between Taiwan and China were regularly finding bones in their nets. Between 70 to 10 ka and 190 to 130 ka ago much lower sea level due to continental ice cap formation exposed the Penghu seabed. Animals and humans were thus able to move between the East Asian mainland and what is now Taiwan. The bones brought to the surface included those of elephants, water buffaloes and tigers, but one was clearly a human lower jawbone (mandible). Its shape and large molar teeth are very different from modern human mandibles and molars. A multinational team from Japan, Denmark, Taiwan and Ireland has extracted proteins from the mandible to check its genetic affinities (Tsutaya, T. and 14 others 2025. A male Denisovan mandible from Pleistocene Taiwan. Science, v. 388, p. 176-180; DOI: 10.1126/science.ads3888). Where DNA has not been preserved in bones proteomics is a useful tool, especially if results are matched with other bones that have yielded both DNA and protein sequences. In the case of the Penghu mandible, proteins from its teeth matched those of Denisovans from the Denisova Cave in Siberia which famously yielded the genome of this elusive human group. They also matched proteins from a rib found in Tibet associated with Denisovan mitochondrial DNA in cave sediments that enclosed the bones.

The three sites (Denisova, Baishiya Cave in Tibet and Penghu Channel) that have produced plausible Denisovan specimens span a large range of latitudes and altitudes. This suggests that Denisovans were capable of successful subsistence across much of East Asia. The Penghu mandible and teeth are similar to several hominin specimens from elsewhere in China that hitherto have been attributed to H. erectus. Apart from the Denisovan type locality, most of the sites have yet to be accurately dated. Having been immersed in sea water for thousands of years isotopes used in dating have been contaminated in the Panghu specimen. It can only be guessed to have lived when the seabed from which it was recovered was dry land; i.e. between 70 to 10 ka and 190 to 130 ka. China was undoubtedly occupied by Homo erectus during the early Pleistocene, but much younger fossils have been attributed to that species by Chinese palaeoanthropologists. Could it be that they are in fact Denisovans? Maybe such people independently developed the Quina knapping technique

See also: Marwick, B. 2025. Unknown human species in East Asia used sophisticated tools at the same time Neanderthals did in Europe. Live Science, 31 March 2025; Ashworth. J. 2025. Denisovan jawbone helps to reveal appearance of ancient human species. Natural History Museum News 11 April 2025.

A fully revised edition of Steve Drury’s book Stepping Stones: The Making of Our Home World can now be downloaded as a free eBook

More dinosaur trackways from the Jurassic of the Isle of Skye, Scotland

Published on April 7, 2025April 8, 2025 by zooks777Leave a comment

The Isle of Skye off the northwestern coast of Scotland is one of several areas in Britain that are world-class geological gems. Except for the Cuillin Hills that require advanced mountaineering skills it is easy to explore and has become a major destination for both beginners and expert geoscientists of all kinds. Together with the adjacent Isle of Raasay the area is covered by a superb, free geological guidebook (Bell, B. 2024. The Geology of the Isles of Skye and Raasay. Geological Society of Glasgow) together with 60 standalone excursion guides, and even an introduction to Gaelic place names and pronunciation. It is freely available from https://www.skyegeology.com/

Fig Dinosaur trackways at Prince Charles’s Point on the Isle of Skye: Left carnivorous theropods; Right herbivorous sauropods. The black scales are 1 m long. The images are enhanced fine-scale elevation models of the exposed surfaces that were derived from vertical photographs. Credit: Blakesley et al., Figs 9 and 27.

Since 2018 Skye has also become a must-visit area for vertebrate palaeontologists. Beneath Palaeocene flood basalts is a sequence of Jurassic strata, both shallow marine and terrestrial. One formation, the Great Estuarine Group of Middle Jurassic (Bathonian, 174–164 Ma) age covers the time when meat-eating theropod- and herbivorous sauropod dinosaurs began to grow to colossal sizes from diminutive forebears. While other Jurassic sequences on Skye have notable marine faunas, its Bathonian strata have yielded a major surprise: some exposed bedding surfaces are liberally dotted with trackways of the two best known groups of dinosaur. The first to be discovered were at Rubha Nam Brathairean (Brothers’ Point) suggesting a rich diversity of species that had wandered across a wide coastal plain, also including the somewhat bizarre Stegosaurus. The latest finds are from a rocky beach at Prince Charles’s Point where the Young Pretender to the British throne, Charles Edward Stuart, landed and hid during his flight from the disastrous Battle of Culloden (16 April 1746). It was only in the last year or so that palaeontologists from the universities of Edinburgh and Liverpool, and the Staffin Museum came across yet more footprints (131 tracks) left there by numerous dinosaurs in the rippled sands of a Bathonian lagoon (Blakesley, T. et al. 2025. A new Middle Jurassic lagoon margin assemblage of theropod and sauropod dinosaur trackways from the Isle of Skye, Scotland. PLOS One, v. 20, article e0319862; DOI: 10.1371/journal.pone.0319862.

The Prince Charles’s Point site is partly covered by large basalt boulders, which perhaps account for the excellent preservation of the bedding surfaces from wave action. Two kinds of footprint are preserved (see image): those made by three-toed feet and by elephant-like feet that ‘squidged-up’ sediment surrounding than. Respectively these are suggested to represent the hind limbs of bipedal carnivorous theropods and quadrupedal herbivorous sauropods. They show that individual dinosaurs moved in multiple directions, but there is no evidence for gregarious behaviour, such as parallel trackways of several animals. They occur on two adjacent bedding surfaces so represent a very short period of time, perhaps a few days. The authors suggest that several individual animals were milling around, with more sauropods than theropods. What such behaviour represents is unclear. The water in an estuarine lagoon would likely have been fresh or brackish. They may have been drinking or perhaps there was some plants or carcases worth eating ? That might explain both kinds of dinosaurs’ milling around. The sizes of both sauropod and theropod prints average about 0.5 m. The stride lengths of the theropods suggest that they were between 5 to 7 metres long with a hip height of around 1.85 m. Their footprints resemble those reconstructed from skeletal remains of Middle Jurassic Megalosaurus, the first dinosaur to be named (by William Buckland in 1827). The sauropods had estimated hip heights of around 2 m so they may have been similar in size (around 16 m) to the Middle Jurassic Cetiosaurus, the first sauropod to be named (by Richard Owen in 1842).

A fully revised edition of Steve Drury’s book Stepping Stones: The Making of Our Home World can now be downloaded as a free eBook

What drove the Cambrian Explosion?

Published on March 28, 2025 by zooks777Leave a comment

The origin of animals occurred sometime during the Proterozoic Eon, perhaps as early as 2.1 Ga (billion years ago) after the Great Oxygenation Event. Available oxygen is a prerequisite for animal life, and that is about as far back as palaeobiologists can push it. More familiar are the trace fossils known as the Ediacaran fauna which emerged after the environmentally highly stressful Cryogenian Period that was marked by two Snowball Earth events. Traces of these animals may have been big enough to be easily found, but they were not particularly diverse and are difficult to place in any particular modern group. Most modern animals have front- and rear ends, tops and bottoms, and input and output orifices. The earliest of these bilaterian beasts may have emerged during the Ediacaran as well, but were not very prepossessing. It was during the Cambrian Period (541 to 485 Ma) that most modern animal phyla became recognisable to palaeobiologists. That carnival of diversification is widely known as the Cambrian Explosion. Yet it was later in geological time that the full panoply of Phanerozoic diversity among taxa below the level of the phylum truly exploded, punctuated by mass extinctions and the diversification that followed each of them. So, what lay behind the initial emergence of the characteristics that form the basic templates of the phyla themselves?

Cartoon of the Cambrian Explosion in benthic faunas. Credit: Gabriela Mangano and Luis A. Buatois, 2016 The Cambrian Explosion, Fig 3.15

A multinational team of modellers and geoscientists have moved the focus from long-term shifts in climate and atmospheric chemistry to what might change from day to night in an ecosystem during the diel cycle (Hammarlund, E.U. and 13 others 2025. Benthic diel oxygen variability and stress as potential drivers for animal diversification in the Neoproterozoic-Palaeozoic Nature Communications, v. 16, article 2223; DOI:10.1038/s41467-025-57345-0). During the Neoproterozoic oxygen levels in Earth atmosphere rose to about half the amount present today. But animals arose and evolved in sea water. The most prolific source of food for them would have been in shallow water (the benthic zone), simply because sunlight in the photic zone encourages photosynthesis. As well as a thriving base for animal life’s food chain shallow water is where oxygen is produced; but only during daylight hours. At night decay of organic matter on the seabed draws down dissolved oxygen. Emma Hammarlund and colleagues wondered if day-night changes in oxygen levels might have exerted sufficient stress to force early animals to adapt and thus diversify. Their model shows that in warm, shallow water the lower oxygen levels at the start of the Phanerozoic could change dramatically in the diel cycle. Algae at the base of the food chain would swiftly oxygenate the water in daylight, but at night would consume it to produce much lower levels. Animals that were better adapted to the stress of this daily ‘feast-and-famine’ cycle in oxygen availability would outcompete others that were less resilient for the available nutrients. Environmental stress had flipped from an obstacle to evolution to a catalyst for it. The earliest appearances of organisms in the 10 modern phyla seem to coincide with global warming at low latitudes to an air temperature of about 25° C at the start of the Cambrian, perhaps when this shift began.

Another empirical coincidence lies in the sedimentary rock record. On modern continents the base of Phanerozoic sediments is widely marked by shallow-water sandstones often at an unconformity. Often white and containing abundant burrows, the sandstones are signs of abundant life, though rarely contain body fossils. They represent global sea-level rise that flooded the existing continents, so the highly productive benthic environment became about four times more widespread at the end of the Cambrian than it was during the previous Ediacaran Period. Abundant life forms were under stress more or less everywhere. Thereafter these ‘shelf seas’ halved in total area, but the basic ‘templates’ for animal life were well-established and the numbers of classes, orders, families etcetera steadily burgeoned. By the end of the Cambrian oxygen production rose so that atmospheric concentration of the gas reached 25%, higher then it is at present.

See also: Hammarlund, E. 2025. How dramatic daily swings in oxygen shaped early animal life. The Conversation, 21 March 2025.

The earliest known impact structure

Published on March 20, 2025 by zooks777Leave a comment

Earth has been through a great many catastrophes, but the vast majority of those of which we know were slow-burning in a geological sense. They resulted in unusually high numbers of extinctions at the species- to family levels over a few million years and the true mass extinctions seem to have been dominated by build ups of greenhouse gases emitted by large igneous provinces. Even the most famous at the end of the Cretaceous Period, which did for the dinosaurs and considerably more organisms that the media hasn’t puffed, was partly connected to the eruption of the Deccan flood basalts of western India. Yet the event that did the real damage was a catastrophe that appeared in a matter of seconds: the time taken for the asteroid that gouged the Chicxulub crater to pass through the atmosphere. Its energy was huge and because it was delivered in such a short time its sheer power was unimaginable. Gradually geologists have recognised signs of an increasing number of tangible structures produced by Earth’s colliding with extraterrestrial objects, which now stands at 190 that have been confirmed.

The frequency of impact craters falls off with age, most having formed in the last ~550 million years (Ma) during the Phanerozoic Eon, only 25 being known from the Precambrian, which spanned around 88 percent of geological time. That is largely a consequence of the dynamic processes of tectonics, erosion and sedimentation that may have obliterated or hidden a larger number. Earth is unique in that respect, the surfaces of other rocky bodies in the Solar System showing vastly more. The Moon is a fine example, especially as it has been Earth’s companion since it formed 4.5 billion years ago (Ga) after the proto-Earth collided with a now vanished planet about the size of Mars. The relative ages of lunar impact structures combined with radiometric ages of the surfaces that they hit has allowed the frequency of collisions to be assessed through time. Applied to the sizes of the craters such data can show how the amount of kinetic energy inflicted on the lunar surface has changed with time. During what geologists refer to as the Hadean Eon (before 4 Ga), the moon underwent continuous bombardment that reached a crescendo between 4.1 and about 3.8 Ga. Thereafter impacts tailed off. Always having been close to the Moon, the Earth cannot have escaped the flux of objects experienced by the lunar surface. Because of Earth’s much greater gravitation pull it was probably hit by more objects per unit area. Apart from some geochemical evidence from Archaean rocks (see: Tungsten and Archaean heavy bombardment; July 2002) and several beds of 3.3 Ga old sediment in South Africa that contain what may have been glassy spherules there are no signs of actual impact structures earlier than a small crater dated at around 2.4 Ga in NE Russia.

Shatter cones in siltstone near Marble Bar in the Pilbara Province: finger for scale. Credit: Kirkland *et al*.; Fig 2a

Now a group of geologists from Curtin University, Perth Western Australia, and the Geological Survey of Western Australia have published their findings of indisputable signs of an impact site in the northern part of Western Australia (Kirkland, C.L. et al. 2025. A Paleoarchaean impact crater in the Pilbara Craton, Western Australia. Nature Communications, v. 16, article 2224; DOI: 10.1038/s41467-025-57558-3). In fact there is no discernible crater at the locality, but sedimentary strata show abundant evidence of a powerful impact in the form of impact-melt droplets in the form of spherules together with shatter cones. These structures form as a result of sudden increase in pressure to 2 to 30 GPa: an extreme that can only be generated in underground nuclear explosions, and thus likely to bear witness to large asteroid impacts. The shocked rocks are immediately overlain by pillow lavas dated at 3.47 Ga, making the impact the earliest known. It has been speculated that impacts during the Archaean and Hadean Eons helped create conditions for the complex organic chemistry that eventually to the first living cells. Considering that entry of hypervelocity asteroids into the early Earth’s atmosphere probably caused such compression that temperatures were raised by adiabatic heating to about ten times that of the Sun’s surface, their ‘entry flashes’ would have sterilised the surface below; the opposite of such notions. Impacts may, however, have delivered both water and simple, inorganic hydrocarbons. Together with pulverisation of rock to make ‘fertiliser’ elements (e.g. K and P) more easily dissolved, they may have had some influence. Their input of thermal energy seems to me to be of little consequence, for decay of unstable isotopes of U, Th and K in the mantle would have heated the planet quite nicely and continuously from Year Zero onwards.

A fully revised edition of Steve Drury’s book Stepping Stones: The Making of Our Home World can now be downloaded as a free eBook

Bone tools widened hominins foraging options 1.5 Ma ago

Published on March 14, 2025March 13, 2025 by zooks777Leave a comment

Hominins have been making and using stone tools since at least 3.4 Ma, as shown by cut marks on bones and stone artefacts themselves. I use the sack term ‘hominin’ because the likely makers and users of the oldest tools are either australopithecines or paranthropoids, there being no fossils designates to the genus Homo of late-Pliocene age. So it might seem un-newsworthy to report that the oldest tools deliberately made from bone are now known to occur in 1.5 Ma old sediments from the famous sedimentary sequence at Olduvai Gorge in Tanzania (de la Torre, I and 8 others2025. Systematic bone tool production at 1.5 million years ago. Nature, v. 639; DOI: 10.1038/s41586-025-08652-5). To be clear, there is abundant evidence that hominins had used bones, especially sturdy long bones, for digging perhaps, much earlier in hominin history. Again, paranthropoids have been implicated in their use. The bones found at Olduvai actually show signs of manufacture into useful objects prior to their use: they show clear signs of knapping to produce points and blades. The bones are among the sturdiest known from the Pleistocene, being from elephants and hippos. Before de la Torre and colleagues found what is essentially a bone-tool factory, it was thought that systematic use of bones in such a sophisticated manner only arose between 400 to 250 ka ago among early Homo in Europe. Sadly, fossils of whoever made the tools were not found at the site. Once again, paranthropoids as well as early Homo are known to have cohabited the area at that time.

‘Front, back and side’ views of a 1.5 Ma old tool made from an elephant humerus – its upper foreleg. The scale bar represents 5 cm. (Credit: de la Torre et al.; Fig 3a)

Bifacial Acheulean stone artefacts first appear in the rock record about 300 ka before these bone tools were made. So one idea that the authors put forward is that the same kind of stone knapping technique was transferred to the more abundant massive bones of the East African Pleistocene megafauna (in the absence or rarity of suitable blocks of stone?). But it remains unclear whether or not such tools were simply selected from very large bones smashed to get at their nutritious marrow. The first possibility implies a cultural shift, whereas the latter points simply to expedience. The authors are at pains to point out that the curious million-year gap in the record of bone tools may be ascribed either to the disappearance of bone technology or simply to archaeologists who worked elsewhere having not regarding bone fragments as the products of skills. That applies equally to earlier times, when bones were indeed used, though with not so much in the way of a ‘mental template’. As de la Torre et al. conclude ‘Future research needs to investigate whether similar bone tools were already produced in earlier times, persisted during the Acheulean and eventually evolved into Middle Pleistocene bone bifaces similar in shape, size and technology to their stone counterparts’.

Direct measurements of ancient atmospheric composition

Published on March 13, 2025 by zooks777Leave a comment

For decades, research into the composition of the Earth’s early atmosphere depended on indirect means. An example is the preservation of water-worn grains of sulphides and uranium oxides in coarse terrestrial sediments older than about 2,200 Ma. Their survival on the continental surface suggested that the atmosphere before then had vanishingly low O₂. Such grains would have otherwise been broken down by oxidation reactions. Younger sediments simply do not contain such detrital grains. This suggested the appearance of an oxidising atmosphere around 2.2 Ga ago: the Great Oxygenation Event. The greenhouse gases – carbon dioxide and methane – are also difficult to estimate directly, especially in the Precambrian. Once plants colonised the land surface, their photosynthesis depended on inhaling and exhaling air through stomata on the surface of leaves (see: Ancient CO₂ estimates worry climatologists; January 2017). The number of stomata per unit area of a leaf surface is expected to increase with lowering of atmospheric CO₂ and vice versa, which has been observed in plants grown in different air compositions. By comparing stomatal density in fossilised leaves of modern plants back to 800 ka allows the change to be calibrated against the record of CO₂ inside air bubbles trapped in ice-cores. This proxy method has given a guide to CO2 variations through the Cenozoic, Mesozoic and upper Palaeozoic Eras. However, the reliability of extinct plant leaves as proxies is suspect.

A fluid inclusion (about 0.2 mm) trapped in a crystal of halite (NaCl). Credit: alchetron.com

Is it possible to find air trapped by other means than in glacial ice? It may be. Tiny pockets of liquid and gas – fluid inclusions – are often found in minerals that crystallised at the Earth’s surface. The most common are crystals of salt (NaCl) and carbonates from ancient lake deposits. A 2019 study revealed that Late Triassic carbonates from Colorado, USA record an increase of atmospheric oxygen levels from 15 to 19% about 215 Ma ago over a period of just 3 million years as dinosaurs first spread into North America, then at equatorial latitudes in the Pangaea supercontinent. This sudden increase in the availability of oxygen may also be linked to the trend towards larger and larger dinosaurs worldwide. Going further back in time trace-metal chemistry of 1,400 Ma old marine sediments from China indicates oxygenated water that suggests an atmospheric oxygen level greater than 4% of that at present. Small as that might seem, it would have been sufficient to sustain animal respiration about half a billion years before the first evidence for the earliest animals. Further work on ancient salt and carbonate deposits confirms much higher oxygen levels than geochemists have expected previously.

Source: Voosen, P, 2025. Earth’s rocks hold whiffs of air from billions of years ago. Science, v.387, articlezhst73x; DOI: 10.1126/science.zhst73x

Life’s origins: a new variant on Darwin’s “warm little pond”

Published on March 3, 2025 by zooks777Leave a comment

In 1871 Charles Darwin wrote to his friend Joseph Hooker, a botanist:

“It is often said that all the conditions for the first production of a living organism are now present, which could ever have been present. But if (& oh what a big if) we could conceive in some warm little pond with all sorts of ammonia & phosphoric salts, light, heat, electricity &c present, that a protein compound was chemically formed, ready to undergo still more complex changes, at the present day such matter w^d be instantly devoured, or absorbed, which would not have been the case before living creatures were formed.”

There have been several attempts over the last 150 years, starting with Miller and Urey in 1952, to create physical analogues for this famous insight (See: The origin of life on Earth: new developments). What such a physico-chemical environment on the early Earth could have been like has also been a fertile topic for discussion: literally warm pools at the surface; hot springs; seawater around deep-ocean hydrothermal vents; even droplets in clouds in the early atmosphere. Attention has recently moved to Darwin’s original surface pools through examination of modern ones. The most important content would be dissolved phosphorus compounds, because that element helps form the ‘backbone’ of the helix structure of RNA and DNA. But almost all natural waters today have concentrations of phosphorus that are far too low for such linkages to form by chemical processes, and also to produce lipids that form cell membranes and the ATP (adenosine triphosphate) so essential in all living metabolism. Phosphorus availability has been too low for most of geological time simply because living organisms are so efficient at removing what they need in order to thrive.

Mono Lake in semi-arid eastern California – a ‘soda lake’- is so concentrated by evaporation that pillars of carbonate grow above its surface

For the first life to form, phosphorus would somehow have had to be concentrated in watery solution as phosphate ions – [PO ₄]³⁻. The element’s source, like that of all others in the surface environment, is in magmas and the volcanic rocks that they form. Perhaps early chemical weathering or reactions between lavas and hydrothermal fluids could have released phosphate ions to solution from a trace mineral present in all lavas: the complex phosphate apatite (Ca₁₀(PO₄)₆(OH,F,Cl)₂). But that would still require extreme concentration for it to be easily available to the life-forming process. In January 2024 scientists at the University of Washington in Seattle, USA (Haas, S. et al. 2024. Biogeochemical explanations for the world’s most phosphate-rich lake, an origin-of-life analog. Nature Communications, v. 5, article 28; DOI: 10.1038/s43247-023-01192-8) showed that the highest known concentrations of dissolved phosphorus occur in the so called “soda lakes” that are found in a variety of modern environments, from volcanically active continental rifts to swampy land. They contain dissolved sodium carbonate (washing soda) at very high concentrations so that they are extremely alkaline and often highly salty. Usually, they are shallow and have no outlet so that dry weather and high winds evaporate the water. Interestingly, the streams that flow into them are quite fresh, so soda lakes form where evaporation exceeds annual resupply of rainwater.

The high evaporation increases the dissolved content of many ions in such lakes to levels high enough for them for them to combine and precipitate calcium, sodium and magnesium as carbonates. In some, but not all soda lakes, such evaporative concentration also increases their levels of dissolved phosphate ions higher than in any other bodies of water. That is odd, since it might seem that phosphate ions should combine with dissolved calcium to form solid calcium phosphate making the water less P-rich. Haas et al. found that lakes which precipitate calcium and magnesium together in the form of dolomite (Ca,Mg)CO₃ have high dissolved phosphate. Removal of Ca and other metal ions through bonding to carbonate (CO₃) deprives dissolved phosphate ions in solution of metal ions with which they can bond. But why has dissolved phosphate not been taken up by organisms growing in the lakes: after all, it is an essential nutrient. The researchers found that some soda lakes that contain algal mats have much lower dissolved phosphate – it has been removed by the algae. But such lakes are not as salty as those rich in dissolved phosphate. They in turn contain far less algae whose metabolism is suppressed by high levels of dissolved NaCl (salt). Hass et al.’s hypothesis has now been supported by more research on soda lakes.

In an early, lifeless world phosphate concentrations in alkaline, salty lakes would be controlled by purely inorganic reactions. This strongly suggests that ‘warm little soda lakes’ enriched in dissolved sodium carbonate by evaporation, and which precipitated dolomite could have enabled phosphorus compounds to accumulate to levels needed for life to start. They might have been present on any watery world in the cosmos that sustained volcanism.

See also: Service, R.F. 2025. Early life’s phosphorus problem solved? Science, v. 387, p. 917; DOI: 10.1126/science.z78227f; Soda Lakes: The Missing Link in the Origin of Life? SciTechDaily, 26 January 2024. .

A fully revised edition of Steve Drury’s book Stepping Stones: The Making of Our Home World can now be downloaded as a free eBook

Modelling climate change since the Devonian

Published on February 24, 2025 by zooks777Leave a comment

A consortium of geoscientists from Australia, Britain and France, led by Andrew Merdith of the University of Adelaide examines the likely climate cooling mechanisms that may have set off the two great ‘icehouse’ intervals in the last 541 Ma (Merdith, A.S. et al. 2025. Phanerozoic icehouse climates as the result of multiple solid-Earth cooling mechanisms. Science Advances, v. 11, article eadm9798: DOI: 10.1126/sciadv.adm9798). They consider the first to be the global cooling that began in the latter part of the Devonian culminating in the Carboniferous-Permian icehouse. The second is the Cenozoic global cooling to form the permanent Antarctic ice cap around 34 Ma and culminated in cyclical ice ages on the northern continents after 2.4 Ma during the Pleistocene. They dismiss the 40 Ma long, late Ordovician to early Silurian glaciation that left its imprint on North Africa and South America – then combined in the Gondwana supercontinent. The data about two of the parameters used in their model – the degree of early colonisation of the continents by plants and their influence on terrestrial weathering are uncertain in that protracted event. Yet the Hirnantian glaciation reached 20°S at its maximum extent in the Late Ordovician around 444 Ma to cover about a third of Gondwana: it was larger than the present Antarctic ice cap. For that reason, their study spans only Devonian and later times.

Fluctuation in evidence for the extent of glacial conditions since the Devonian: the ‘ice line’ is grey. The count of glacial proxy occurrences in each 10° of latitude through time is shown in the colour key. Credit: Merdith et al., Fig 2A.

Merdith et al. rely on four climatic proxies. The first of these comprises indicators of cold climates, such as glacial dropstones, tillites and evidence in sedimentary rocks of crystals of hydrated calcium carbonate (ikaite – CaCO₃.6H₂O) that bizarrely forms only at around 0°C . From such occurrences it is possible to define an ‘ice line’ linking different latitudes through geological time. Then there are estimates of global average surface temperature; low-latitude sea surface temperature; and estimates of atmospheric CO₂. The ‘ice-line’ data records an additional, long period of glaciation in the Jurassic and early Cretaceous, but evidence does not extend to latitudes lower than 60°. It is regarded by Merdith et al. as an episode of ‘cooling’ rather than an ‘icehouse’. Their model assesses sources and sinks of CO₂since the Devonian Period.

The main natural source of the principal greenhouse gas CO₂ is degassing through volcanism expelled from the mantle and breakdown of carbonate rock in subducted lithosphere. Natural sequestration of carbon involves weathering of exposed rock that releases dissolved CO₂ and ions of calcium and magnesium. A recently compiled set of plate reconstructions that chart the waxing and waning of tectonics since the Devonian Period allows them to model the tectonically driven release of carbon over time, with time scales on the order of tens to hundreds of Ma. The familiar Milanković forcing cycles on the order of tens to hundreds of ka are thus of no significance in Merdith et al.’s broader conception of icehouse episodes Their modelling shows high degassing during the Cretaceous, modern levels during the late Palaeozoic and early Mesozoic, and low emissions during the Devonian. The model also suggests that cooling stemmed from variations in the positions and configuration of continents over time. Another crucial factor is the tempo of exposure of rocks that are most prone to weathering. The most important are rocks of the ocean lithosphere incorporated into the continents to form ophiolite masses. The release of soluble products of weathering into ocean basins through time acts as a fluctuating means of ‘fertilising’ so that more carbon can be sequestered in deep sediments in the form of organisms’ unoxidised tissue and hard parts made of calcium carbonates and phosphates. Less silicate weathering results in a boost to atmospheric CO₂.

Only two long, true icehouse episodes emerge from the empirical proxy data, expressed by the ‘ice-line’ plots. Restricting the modelling to single global processes that might be expected to influence degassing or carbon sequestration produces no good fits to the climatic proxy data. Running the model with all the drivers “off” produces more or less continuous icehouse conditions since the Devonian. The model’s climate-related outputs thus imply that many complex processes working together in syncopation may have driven the gross climate vagaries over the last 400 Ma or so. A planet of Earth’s size without such complexity would throughout that period have had a high-CO₂ warm climate. According to Andrew Merdith its fluctuation from greenhouse to icehouse conditions in the late Palaeozoic and the Cenozoic were probably due to “coincidental combination of very low rates of global volcanism, and highly dispersed continents with big mountains, which allow for lots of global rainfall and therefore amplify reactions that remove carbon from the atmosphere”.

Geological history is, almost by definition, somewhat rambling. So, despite despite the large investment in seeking a computed explanation of data drawn from the record, the outcome reflects that in a less than coherent account. To state that many complex processes working at once may have driven climate vagaries over the last 400 Ma or so, is hardly a major advance: palaeoclimatologists have said more or less the same for a couple of decades or more, but have mainly proposed single driving mechanisms. One aspect of Merdith et al.’s results seems to be of particular interest. ‘Icehouse’ conditions seem to be rare events interspersed with broader ice-free periods. We evolved within the mammal-dominated ecosystems on the continents during the latest of these anomalous climatic episodes. And we and those ecosystems now rely on a cool world. As the supervisor of the project commented, ‘Over its long history, the Earth likes it hot, but our human society does not’.

Readers may like to venture into how some philosophers of science deal with a far bigger question; ‘Is intelligent life a rare, chance event throughout the universe?’ That is, might we be alone in the cosmos? In the same issue of Science Advances is a paper centred on just such questions (Mills, D.B. et al. 2025. A reassessment of the “hard-steps” model for the evolution of intelligent life. Science Advances, v. 11, article eads5698; DOI: 10.1126/sciadv.ads5698). It stems from cosmologist Brandon Carter’s ‘Anthropic Principle’ first developed at Nicolas Copernicus’s 500^th birthday celebrations in 1973. This has since been much debated by scientists and philosophers – a gross understatement as it knocks the spots off the Drake Equation. To take the edge off what seems to be a daunting task, Mills et al. consider a corollary of the Anthropic Principle, the ‘hard steps model’. That, in a nutshell, postulates that the origin of humanity and its ability to ponder on observations of the universe required a successful evolutionary passage through a number of hard steps. It predicts that such intelligence is ‘exceedingly rare’ in the universe. Icehouse conditions are respectable candidates for evolutionary ‘hard steps’, and in the history of Earth there have been five of them.

A fully revised edition of Steve Drury’s book Stepping Stones: The Making of Our Home World can now be downloaded as a free eBook

A cure for the Great British Pothole Plague?

Published on February 6, 2025 by zooks777Leave a comment

Anyone who read the manifestos of the mainstream political parties in the UK – there may not be many who did – would have been amused to see that all promised to resolve the plague of potholes in the countries roads, both major and minor. For decades road users have been alarmed when hitting a pothole and in some cases had damage inflicted on their vehicles, and in the case of those on two wheels, on themselves. The RAC (Royal Automobile Club) has estimated that there are, on average, six potholes per mile on Britain’s roads: the greatest density in Europe. The AA (Automobile Association) estimated that almost £0.6 billion was spent in 2024 repairing pothole-damaged vehicles. This is not a new phenomenon. Before the advent of turnpike trusts in the late 18^th century, which maintained roads travelled by Britain’s mail coach services, it was not uncommon to encounter potholes up to two metres deep. Legend has it that on one such route through northern Nottinghamshire two coach horses fell into a pothole and drowned. Scottish engineer, John Loudon McAdam invented a solution around 1820: crushed stone laid on the road surface in slightly convex layers, the topmost being bonded with stone dust. This ‘macadam’ surface created cambered highways that drained rainwater to the sides and downwards. Modern roads are still based on that principle, with the addition of tar or bitumen to the top layer to produce a hard, impermeable surface, which also prevents aggregate and dust being sucked from the surface by fast moving vehicles.

So, why the potholes? Several reasons: increased traffic; heavier vehicles; less maintenance; patching rather than resurfacing. Most important: the materials and the weather. Dry, hot weather softens the bitumen and drives out volatile hydrocarbons making the bitumen less plastic. The pounding of tyres in cooler weather fractures the now stiffened bitumen, mainly at microscopic scales. Wetting of the tarmac seeps water into the microfractures. The formation of ice films jacks opens the microfractures and produces more in the cold stiff bitumen, eventually to separate the particles of aggregate in the asphalt. The wearing course begins to crumble so that aggregate grains escape and scatter. Thus weakened, the top layer breaks up into larger fragments and a pit forms to join up with others so that a pothole forms and grows. Wheels of traffic bounce when they cross a pothole, the shock of which causes the centre of degradation to shift and create more cavities. Simply filling the existing potholes merely serves to create new ones: a vicious cycle that can only be broken by complete resurfacing: the traffic cones come out!.

All this has been known for well over a century by civil engineers. Around the start of the 21^st century – maybe slightly earlier – it dawned on engineers that the critical problem was degradation of bitumen. A petroleum derivative, occurring naturally as surface seeps in some oilfields, bitumen is chemically complex: a combination of asphaltenes and maltenes (resins and oils). Deterioration of bitumen through evaporation, oxidation and exposure to ultraviolet radiation decreases the maltene content and stiffens the binding agent in asphalt. So the earliest attempts at reducing pothole formation centred on rejuvenation by periodically adding substitutes for maltenes to road surfaces. Diesel (gas-oil) works, but is obviously hazardous. More suitable are vegetable oils such as waste cooking oils or those produced by pyrolysis of cotton, straw, wood waste and even animal manure. The problem is getting the rejuvenators into existing asphalt surfaces: clearly, simply spraying them on the surface seems a recipe for disaster! A solution that dawned on engineers around 2005 was to make bitumen that is ‘self-healing’.

Schematic of the production of microcapsules from club moss spores to contain sunflower oil to be used in self-healing asphalt (Credit: Alpizar-Reyes, E. *et al*. 2022)

Simply mixing rejuvenators into bitumen during asphalt manufacture will not do the trick, for the result would be a weakened binding agent at the outset. For the last 15 years researchers have sought means of adding rejuvenators in porous capsules, to release them as microfractures begin to form: on demand, as it were. There have been dozens of publications about experiments that found ‘sticking points’. However, in early 2025 what seems to be a viable breakthrough splashed in the British press. It was made by an interdisciplinary team of scientists from King’s College London and Swansea University, in collaboration with scientists in Chile. They chemically treated spores of Lycopodium club mosses to perforate their cell walls and clear out their contents to be replaced by sunflower oil, an effective bitumen rejuvenator. Experiments showed that such microcapsules released the oil to heal cracks in aged bitumen samples in around an hour. Mixed into bitumen to be added to asphalt they would remain ‘dormant’ until a microfracture formed in their vicinity released it, thereby making the asphalt binder self healing.

Will such an advance finally resolve the pothole plague? It may take a while …

See: Alpizar-Reyes, E. et al. 2022. Biobased spore microcapsules for asphalt self-healing. ACS Applied Materials & Interfaces, v. 14, p. 31296-31311; DOI: 10.1021/acsami.2c07301

A fully revised edition of Steve Drury’s book Stepping Stones: The Making of Our Home World can now be downloaded as a free eBook

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