The peptide bond that holds life together may have an interstellar origin

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In the 1950s Harold Urey of the University of Chicago and his student Stanley Miller used basic lab glassware containing 200 ml of water and a mix of the gases methane (CH4), ammonia (NH3) and hydrogen sulfide (H2S) to model conditions on the early Earth. Heating this crude analogue for ocean and atmosphere and continuous electrical discharge through it did, in a Frankensteinian manner, generate amino acids. Repeats of the Miller-Urey experiment have yielded 10 of the 20 amino acids from which the vast array of life’s proteins have been built. Experiments along similar lines have also produced the possible precursors of cell walls – amphiphiles. In fact, all kinds of ‘building blocks’ for life’s chemistry turn up in analyses of carbonaceous chondrite meteorites and in light spectra from interstellar gas clouds. The ‘embarrassment of riches’ of life’s precursors from what was until the 20th century regarded as the ‘void’ of outer space lacks one thing that could make it a candidate for life’s origin, or at least for precursors of proteins and the genetic code DNA and RNA. Both kinds of keystone chemicals depend on a single kind of connector in organic chemistry.

Reaction between two molecules of the amino acid glycene that links them by a peptide bond to form a dipeptide. (Credit: Wikimedia Commons)

Molecules of amino acids have acidic properties (COOH – carboxyl) at one end and their other end is basic (NH2 – amine). Two can react by their acid and basic ‘ends’ neutralising. A hydroxyl (OH–) from carboxyl and a proton (H+) from amine produce water. This gives the chance for an end-to-end linkage between the nitrogen and carbon atoms of two amino acids – the peptide bond. The end-product is a dipeptide molecule, which also has carboxyl at one end and amine at the other. This enables further linkages through peptide bonds to build chains or polymers based on amino acids – proteins. Only 20 amino acids contribute to terrestrial life forms, but linked in chains they can form potentially an unimaginable diversity of proteins. Formation of even a small protein that links together 100 amino acids taken from that small number illustrates the awesome potential of the peptide bond. The number of possible permutations and combinations to build such a protein is 20100 – more than the estimated number of atoms in the observable universe! Protein-based life has almost infinite options: no wonder that ecosystems on Earth are so diverse, despite using a mere 20 building blocks. Simple amino acids can be chemically synthesised from C, H, O and N. About 500 occur naturally, including 92 found in a single carbonaceous chondrite meteorite. They vastly increase the numbers of conceivable proteins and other chain-molecules analogous to RNA and DNA: a point seemingly lost on exobiologists and science fiction writers!

Serge Kranokutski of the Max Planck Institute for Astronomy at the Friedrich Schiller University in Jena, German and colleagues from Germany, the Netherlands and France have assessed the likelihood of peptides forming in interstellar space in two publications (Kranokutski S.A. and 4 others 2022. A pathway to peptides in space through the condensation of atomic carbon. Nature Astronomy, v, 6, p. 381–386; DOI: 10.1038/s41550-021-01577-9. Kranokutski, S.A. et al. 2024. Formation of extraterrestrial peptides and their derivatives. Science Advances, v. 10, article eadj7179; DOI: 10.1126/sciadv.adj7179). In the first paper the authors show experimentally that condensation of carbon atoms on cold cosmic dust particles can combine with carbon monoxide (CO) and ammonia (NH3) form amino acids. In turn, they can polymerise to produce peptides of different lengths. The second demonstrates that water molecules, produced by peptide formation, do not prevent such reactions from happening. In other words, proteins can form inorganically anywhere in the cosmos. Delivery of these products, through comets or meteorites, to planets forming in the habitable ‘Goldilocks’ zone around stars may have been ‘an important element in the origins of life’ – anywhere in the universe. Chances are that, compared with the biochemistry of Earth, such life would be alien in an absolute sense. There are effectively infinite options for the proteins and genetic molecules that may be the basis of life elsewhere, quite possibly on Mars or the moons of Jupiter and Saturn: should it or its chemical fossils be detectable.

The first Europeans at the Ukraine-Hungary border

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Until this year, the earliest date recorded for the presence of humans in Europe came from the Sierra de Atapuerca in the Province of Burgos, northern Spain. The Sima del Elefante cave yielded a fossil mandible of a human dubbed Homo antecessor from which an age between 1.2 to 1.1 Ma was estimated from a combination of palaeomagnetism, cosmogenic nuclides and stratigraphy. Stone tools from the Vallonet Cave in southern France are around the same age. There is a time gap of about 200 ka before the next sign of human ventures into Europe, probably coinciding with an extreme ice age. They reappear in the form of stone tools and even footprints that they left between 1.0 to 0.78 Ma in ancient river sediments beneath the crumbling sea cliffs of Happisburgh in Norfolk, England. Although no human fossils were preserved, they too have been assigned to H. antecessor.

Topographic map of Europe (click to see full resolution in a new window). The Carpathian Mountains form an arc surrounding the Pannonian Basin (Hungarian Plains) just below centr. Korolevo and other Homo erectus and H. antecessor sites are marked by red spots (Credit: Wikipedia Commons)

In 1974 Soviet archaeologists discovered a site bearing stone tools by the River Tisza at Korolevo in the Carpathian Mountains close to the borders between Ukraine, Romania and Hungary. Korolevo lies at the northeastern edge of the Pannonian Basin that dominates modern Hungary. Whoever left the tools was on the westward route to a huge, fertile area whose game might support them and their descendants. The route along the Tisza leads to the River Danube and then to its headwaters far to the west. Going eastwards leads to the plains north of the Black Sea and eventually via Georgia to the Levant. On that route lies Dmanisi in Georgia, famous for the site where remains of the first hominins (H. erectus, dated at ~1.8 Ma) to leave Africa were found (see: Consider Homo erectus for what early humans achived). The tools from Korolevo are primitive, but have remained undated since 1974. 50 years on, Roman Garba of the Czech Academy of Sciences with colleagues from Czechia, Ukraine, Germany, Australia, South Africa and Denmark have finally resolved their antiquity (Garba, R. and 12 others 2024. East-to-west human dispersal into Europe 1.4 million years ago. Nature v. 627, p. 805–810; DOI: 10.1038/s41586-024-07151-3). Without fossils it is not possible to decide if the tool makers were H. erectus or H. antecessor.

The method used to date the site is based on radioactive 10Be and 26Al formed from oxygen and silicon in quartz grains by cosmic ray bombardment while the grains are at the surface. Since the half life of 26Al (0.7 Ma) is less than that of 10Be (1.4 Ma), after burial the 26Al/10Be ratio decreases and is a guide to the age of the sediment layer that contains the quartz grains. In this case the ag is quite precise (1.42 ± 0.28 Ma). The decreasing age of H. erectus or H. antecessor sites from the 1.8 Ma of Dmanisi in Georgia in the east, through 1.4 Ma (Korolevo) to 1.2 in Spain and France could mark the slow westward migration of the earliest Europeans. It is tempting to suggest possible routes as Garba et al. have. But such sparse and widely separated sites can yield very little certainty. Indeed, it is equally likely that each known site marks the destination of separate migrations at different times that ended in population collapse. The authors make an interesting point regarding the Korolevo population. They were there at a time when three successive interglacials were significantly warmer than the majority during the Early Pleistocene. Also glacial cycles then had ~41 ka time spans before the transition to 100 ka about 1 Ma ago. Unfortunately, no information about the ecosystem that the migrants exploited is available

See also: Prostak, S. 2024. 1.4-Million-Year-Old Stone Tools Found in Ukraine Document Earliest Hominin Occupation of Europe. Sci News, 7 March 2024. (includes map showing possible routes of early human dispersal)

Ocean-floor sediments reveal the influence of Mars on long-term climate cycles

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In 1976 three scientists from Columbia and Brown (USA) and Cambridge (UK) Universities published a paper that revolutionised the study of ancient climates (Hays J.D., Imbrie J. and Shackleton N.J. 1976. Variations in the Earth’s Orbit: Pacemaker of the Ice Ages. Science, v. 194, p. 1121-1132;  DOI: 10.1126/science.194.4270.1121). Using variations in oxygen isotopes from foraminifera through two cores of sediments beneath the floor of the southern Indian Ocean they verified Milutin Milankovich’s hypothesis of astronomical controls over Earth’s climate. This centred on changes in Earth’s orbital parameters induced by gravitational effects from the motions of other planets: its orbit’s eccentricity, and the tilt and precession of its rotational axis. Analysis of the frequency of isotopic variations in the resulting time series yielded Milankovich’s predictions of ~100, 41 and 21 ka periodicities respectively. The time spanned by the cores was that of the last 500 ka of the Pleistocene and thus the last 5 glacial-interglacial cycles. Subsequently, the same astronomical climate forcing  has been detected  for various climate-induced changes in the earlier sedimentary record, including the glacial cycles of the Carboniferous and Neoproterozoic, Jurassic climate changes due to oceanic methane emissions and many other types of cyclicity during the Phanerozoic.

One hemisphere of Mars captured by ESA’s Mars Express. Credit: ESA / DLR / FU Berlin /

As well as time series based on isotopic and other geochemical changes in marine cores, other variables such as thickness of turbidite beds or cyclical repetitions of short rock sequences such as the ‘cyclothems’ of Carboniferous age (repetitions of a  limestone, sandstone, soil, coal sequence) have also been subject to frequency analysis. Sedimentary features that have not been tried are gaps or hiatuses in stratigraphic sequences where strata are missing from a deep-sea sequence. These signify erosion of sediment due to vigorous bottom currents in sequences otherwise dominated by continuous deposition under low-energy conditions. Three geoscientists from the University of Sydney, Australia and the Sorbonne University, France, have subjected records of gaps in Cenozoic sedimentation from 293 deep-sea drill cores to time-series analysis to discover what such ‘big data’ might reveal as regards climate fluctuations on the order of millions of years (Dutkiewicz, A., Boulila, S. & Müller, R.D. 2024. Deep-sea hiatus record reveals orbital pacing by 2.4 Myr eccentricity grand cycles. Nature Communications, v. 15, article 1998; DOI: 10.1038/s41467-024-46171-5).

In theory gravitational interrelationships between all the orbiting planets should have an effect on the orbital parameters of each other, and thus the amount of received solar radiation and changes in global climate. As well as the Milankovich effect, longer astronomical ‘grand cycles’ may therefore have been reflected somehow in Earth’s climatic history (Laskar, J. et al. 2004. A long-term numerical solution for the insolation quantities of the Earth. Astronomy & Astrophysics, v. 428, p. 261-285; DOI: 10.1051/0004-6361:20041335). Based on Laskar et al.’s calculations Adriana Dutkiewicz and colleagues sought evidence for two predicted ‘grand cycles’ that result from orbital interactions between Earth and Mars. These are a 2.4 Ma period in the eccentricity of Earth’s orbit and one of 1.2 Ma in the tilt of its axis.

The authors were able to detect cyclicity in the hiatus time series that is close to the 2.4 Ma Mars-induced waxing and waning of solar heating. Warming would increase mixing of ocean water through cyclones and hurricanes. That would then induce more energetic deep ocean currents and more erosion on the deep ocean floor: more gaps in sedimentation. Cooler conditions would ‘calm’ deep ocean currents so that deposition would outweigh evidence of erosion. The 1.2 Ma axial tilt cyclicity is not apparent in the data. Interestingly, the ~2.4 Ma cyclicity underwent a significant deviation at the Palaeocene-Eocene Boundary’ (56Ma), seemingly predicted by Laskar et al’s  astronomical solutions as a chaotic orbital transition between 56 and 53 Ma. Dutkiewicz et al. also chart the relations between the sedimentary-hiatus time series and major tectonic, oceanographic, and climatic changes during the Cenozoic Era, and found that terrestrial processes did disrupt the Mars-related orbital eccentricity cycles.

The findings suggest that long-term astronomical climate forcing needs to be borne in mind for better understanding the future response of the ocean to global warming. Also, if Mars had such an influence so must have Venus, which is more massive and closer. That remains to be investigated, and also the effects of the giant planets. In the very distant past there behaviour may have resulted in unimaginable astronomical changes. According to the bizarrely named Nice Model a back and forth shuffling of the Giant Planets was probably responsible for the Late Heavy Bombardment 4.1 to 3.8 billion years (Ga) ago. Such errant behaviour may even have triggered the flinging of some of the Sun’s original planetary complement out of the solar system and changed the outward order of the existing eight. Fortunately, the present planetary set-up seems to be stable …

See also: Dutkiewicz, A., & Müller, R. D. 2022. Deep-sea hiatuses track the vigor of Cenozoic ocean bottom currents. Geology, v. 50, p. 710–715; DOI: 10.1130/G49810.1; Mars drives deep-ocean circulation in Earth’s oceans, study suggests. Sci News, 13 March 2024.

How did African humans survive the 74 ka Toba volcanic supereruption?

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The largest volcanic eruption during the 2.5 million year evolution of the genius Homo, about 74 thousand years (ka) ago, formed a huge caldera in Sumatra, now filled by Lake Toba. A series of explosions lasting just 9 to 14 days was forceful enough to blast between 2,800 to 6,000 km3 of rocky debris from the crust. An estimated 800 km3 was in the form of fine volcanic ash that blanketed South Asia to a depth of 15 cm. Thin ash layers containing shards of glass from Toba occur in marine sediments beneath the Indian Ocean, the Arabian and South China Seas. Some occur as far off as sediments on the floor of Lake Malawi in southern Africa. A ‘spike’ of sulfates is present at around 74 ka in a Greenland ice core too. Stratospheric fine dust and sulfate aerosols from Toba probably caused global cooling of up to 3.5 °C over a modelled 5 years following the eruption. To make matters worse, this severe ‘volcanic winter’ occurred during a climatic transition from warm to cold caused by changes in ocean circulation and falling atmospheric CO2 concentration, known as a Dansgaard-Oeschger event.

There had been short-lived migrations of modern humans out of Africa into the Levant since about 185 ka. However, studies of the mitochondrial DNA (mtDNA) of living humans in Eurasia and Australasia suggest that permanent migration began about 60 ka ago. Another outcome of the mtDNA analysis is that the genetic diversity of living humans is surprisingly low. This suggests that human genetic diversity may have been sharply reduced globally roughly around the time of the  Toba eruption. This implies a population bottleneck with the number of humans alive at the time to the order of a few tens of thousands (see also: Toba ash and calibrating the Pleistocene record; December 2012). Could such a major genetic ‘pruning’ have happened in Africa? Over six field seasons, a large team of geoscientists and archaeologists drawn from the USA, Ethiopia, China, France and South Africa have excavated a rich Palaeolithic site in the valley of the Shinfa River, a tributary of the Blue Nile in western Ethiopia. Microscopic studies of the sediments enclosing the site yielded glass shards whose chemistry closely matches those in Toba ash, thereby providing an extremely precise date for the human occupation of the site: during the Toba eruption itself (Kappelman, Y. and 63 others 2024. Adaptive foraging behaviours in the Horn of Africa during Toba supereruption. Nature, v. 627; DOI: 10.1038/s41586-024-07208-3).

Selection of possible arrowheads from the Shinfa River site (Credit: Kappelman et al.; Blue Nile Survey Project)

The artifacts and bones of what these modern humans ate suggest a remarkable scenario for how they lived. Stone tools are finely worked from local basalt lava, quartz and flint-like chalcedony found in cavities in lava flows. Many of them are small, sharp triangular points, some of which show features consistent with their use as projectile tips that fractured on impact; they may be arrowheads, indeed the earliest known. Bones found at the site are key pointers to their diet. They are from a wide variety of animal, roughly similar to those living in the area at present: from monkeys to giraffe, guinea fowl to ostrich, and even frogs. There are remains of many fish and freshwater molluscs. Although there are no traces of plant foods, clearly those people who loved through the distant effects of Toba were well fed. Although a period of global cooling may have increased aridity at tropical latitudes in Africa, the campers were able to devise efficient strategies to obtain victuals. During wet seasons they lived off terrestrial prey animals, and during the driest times ate fish from pools in the river valley. These are hardly conditions likely to devastate their numbers, and the people seem to have been technologically flexible. Similar observations were made at the Pinnacle Point site in far-off South Africa in 2018, where Toba ash is also present. Both sites refute any retardation of human cultural progress 74 ka ago. Rather the opposite: people may have been spurred to innovation, and the new strategies may have allowed them to migrate more efficiently, perhaps along seasonal drainages. In this case that would have led them or their descendants to the Nile and a direct route to Eurasia; along ‘blue highway’ corridors as Kappelman et al. suggest.

Yet the population bottleneck implied by mtDNA analyses is only vaguely dated: it may have been well before or well after Toba. Moreover, there is a 10 ka gap between Toba and the earliest accurately dated migrants who left Africa – the first Australians at about 65 ka. However, note that there is inconclusive evidence that modern humans may have occupied Sumatra by the time of the eruption.  Much closer to the site of the eruption in southeast India, stone artifacts have been found below and above the 74 ka datum marked by the thick Toba Ash. Whether these were discarded by anatomically modern humans or earlier migrants such as Homo erectus remains unresolved. Either way, at that site there is no evidence for any mass die-off, even though conditions must have been pretty dreadful while the ash fell. But that probably only lasted for little more than a month. If the migrants did suffer very high losses to decrease the genetic diversity of the survivors, it seems just as likely to have been due to attrition on an extremely lengthy trek, with little likelihood of tangible evidence surviving. Alternatively, the out-of-Africa migrants may have been small in number and not fully representative of the genetic richness of the Africans who stayed put: a few tens of thousand migrants may not have been very diverse from the outset.

The ‘Anthropocene Epoch’ bites the dust?

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The International Commission on Stratigraphy (ICS) issues guidance for the division of geological history that has evolved from the science’s original approach: that was based solely on what could be seen in the field. That included: variations in lithology and the law of superposition; unconformities that mark interruptions through deformation, erosion and renewed deposition; the fossil content of sediments and the law of faunal succession; and more modern means of division, such as geomagnetic changes detected in rock over time. That ‘traditional’ approach to relative time is now termed chronostratigraphy, which has evolved since the 19th century from the local to the global scale as geological research widened its approach. Subsequent development of various kinds of dating has made it possible to suggest the actual, absolute time in the past when various stratigraphic boundaries formed – geochronology. Understandably, both are limited by the incompleteness of the geological record – and the whims of individual geologists. For decades the ICS has been developing a combination of both approaches that directly correlates stratigraphic units and boundaries with accurate geochronological ages. This is revised periodically, the ICS having a detailed protocol for making changes.  You can view the Cenozoic section of the latest version of the International Chronostratigraphic Chart and the two systems of units below. If you are prepared to travel to a lot of very remote places you can see a monument – in some cases an actual Golden Spike – marking the agreed stratigraphic boundary at the ICS-designated type section for 80 of the 93 lower boundaries of every Stage/Age in the Phanerozoic Eon. Each is a sonorously named Global Boundary Stratotype Section and Point or GSSP (see: The Time Lords of Geology, April 2013). There are delegates to various subcommissions and working groups of the ICS from every continent, they are very busy and subject to a mass of regulations …

Chronostratigraphic Chart for the Cenozoic Era showing the 5 tiers of stratigraphic time division. The little golden spikes mark where a Global Boundary Stratotype Section and Point monument has been erected at the boundary’s type section.

On 11 May 2011, the Geological Society of London hosted a conference, co-sponsored by the British Geological Survey, to discuss evidence for the dawn of a new geological Epoch: the Anthropocene, supposedly marking the impact of humans on Earth processes. There has been ‘lively debate’ about whether or not such a designation should be adopted. An Epoch is at the 4th tier of the chronostratigraphic/geochronologic systems of division, such as the Holocene, Pleistocene, Pliocene and Miocene, let alone a whole host of such entities throughout the Phanerozoic, all of which represent many orders of magnitude longer spans of time and a vast range of geological events. No currently agreed Epoch lasted less than 11.7 thousand years (the Holocene) and all the others spanned 1 Ma to tens of Ma (averaged at 14.2 Ma). Indeed, even geological Ages (the 5th tier) span a range from hundreds of thousands to millions of years (averaged at 6 Ma). Use ‘Anthropocene’ in Search Earth-logs to read posts that I have written on this proposal since 2011, which outline the various arguments for and against it.

In the third week of May 2019 the 34-member Anthropocene Working Group (AWG) of the ICS convened to decide on when the Anthropocene actually started. The year 1952 was proposed – the date when long-lived radioactive plutonium first appears in sediments before the 1962 International Nuclear Test-Ban Treaty. Incidentally, the AWG proposed a GSSP for the base of the Anthropocene in a sediment core through sediments in the bed of Crawford Lake an hour’s drive west of Toronto, Canada.   After 1952 there are also clear signs that plastics, aluminium, artificial fertilisers, concrete and lead from petrol began to increase in sediments. The AWG accepted this start date (the Anthropocene ‘golden spike’) by a 29 to 5 vote, and passed it into the vertical ICS chain of decision making. This procedure reached a climax on Monday 4 March 2024, at a meeting of the international Subcommission on Quaternary Stratigraphy (SQS): part of the ICS. After a month-long voting period, the SQS announced a 12 to 4 decision to reject the proposal to formally declare the Anthropocene as a new Epoch. Normally, there can be no appeals for a losing vote taken at this level, although a similar proposal may be resubmitted for consideration after a 10 year ‘cooling off’ period. Despite the decisive vote, however, the chair of the SQS, palaeontologist Jan Zalasiewicz of the University of Leicester, UK, and one of the group’s vice-chairs, stratigrapher Martin Head of Brock University, Canada have called for it to be annulled, alleging procedural irregularities with the lengthy voting procedure.

Had the vote gone the other way, it would marked the end of the Holocene, the Epoch when humans moved from foraging to the spread of agriculture, then the ages of metals and ultimately civilisation and written history. Even the Quaternary Period seemed under threat: the 2.5 Ma through which the genus Homo emerged from the hominin line and evolvd. Yet a pro-Anthropocene vote would have faced two more, perhaps even more difficult hurdles: a ratification vote by the full ICS, and a final one in August 2024 at a forum of the International Union of Geological Sciences (IUGS), the overarching body that represents all aspects of geology.  

There can be little doubt that the variety and growth of human interferences in the natural world since the Industrial Revolution poses frightening threats to civilisation and economy. But what they constitute is really a cultural or anthropological issue, rather than one suited to geological debate. The term Anthropocene has become a matter of propaganda for all manner of environmental groups, with which I personally have no problem. My guess is that there will be a compromise. There seems no harm either way in designating the Anthropocene informally as a geological Event. It would be in suitably awesome company with the Permian and Cretaceous mass extinctions, the Great Oxygenation Event at the start of the Proterozoic, the Snowball Earth events and the Palaeocene–Eocene Thermal Maximum. And it would require neither special pleading nor annoying the majority of geologists. But I believe it needs another name. The assault on the outer Earth has not been inflicted by the vast majority of humans, but by a tiny minority who wield power for profit and relentless growth in production. The ‘Plutocracene’ might be more fitting. Other suggestions are welcome …

See also: Witze, A. 2024. Geologists reject the Anthropocene as Earth’s new epoch — after 15 years of debate. Nature, v. 627, News article; DOI: 10.1038/d41586-024-00675-8; Voosen, P. 2024. The Anthropocene is dead. Long live the Anthropocene. Science, v. 383, News article, 5 March 2024.

A new explanation for the Neoproterozoic Snowball Earth episodes

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The Cryogenian Period that lasted from 860 to 635 million years ago is aptly named, for it encompassed two maybe three episodes of glaciation. Each left a mark on every modern continent and extended from the poles to the Equator. In some way, this series of long, frigid catastrophes seems to have been instrumental in a decisive change in Earth’s biology that emerged as fossils during the following Ediacaran Period (635 to 541 Ma). That saw the sudden appearance of multicelled organisms whose macrofossil remains – enigmatic bag-like, quilted and ribbed animals – are found in sedimentary rocks in Australia, eastern Canada and NW Europe. Their type locality is in the Ediacara Hills of South Australia, and there can be little doubt that they were the ultimate ancestors of all succeeding animal phyla. Indeed one of them Helminthoidichnites, a stubby worm-like animal, is a candidate for the first bilaterian animal and thus our own ultimate ancestor. Using the index for Palaeobiology or the Search Earth-logs pane you can discover more about them in 12 posts from 2006 to 2023. The issue here concerns the question: Why did Snowball Earth conditions develop? Again, refresh your knowledge of them, if you wish, using the index for Palaeoclimatology or Search Earth-logs. From 2000 onwards you will find 18 posts: the most for any specific topic covered by Earth-logs. The most recent are Kicking-off planetary Snowball conditions (August 2020) and Signs of Milankovich Effect during Snowball Earth episodes (July 2021): see also: Chapter 17 in Stepping Stones.

One reason why Snowball Earths are so enigmatic is that CO2 concentrations in the Neoproterozoic atmospheric were far higher than they are at present. In fact since the Hadean Earth has largely been prevented from being perpetually frozen over by a powerful atmospheric greenhouse effect. Four Ga ago solar heating was about 70 % less intense than today, because of the ‘Faint Young Sun’ paradox. There was a long episode of glaciation (from 2.5 to 2.2 Ga) at the start of the Palaeoproterozoic Era during which the Great Oxygenation Event (GOE) occurred once photosynthesis by oxygenic bacteria became far more common than those that produced methane. This resulted in wholesale oxidation to carbon dioxide of atmospheric methane whose loss drove down the early greenhouse effect – perhaps a narrow escape from the fate of Venus. There followed the ‘boring billion years’ of the Mesoproterozoic during which tectonic processes seem to have been less active. in that geologically tedious episode important proxies (carbon and sulfur isotopes) that relate to the surface part of the Earth System ‘flat-lined’.  The plethora of research centred on the Cryogenian glacial events seems to have stemmed from the by-then greater complexity of the Precambrian Earth System.

Since the GOE the main drivers of Earth’s climate have been the emission of CO2 and SO2 by volcanism, the sedimentary burial of carbonates and organic carbon in the deep oceans, and weathering. Volcanism in the context of climate is a two-edged sword: CO2 emission results in greenhouse warming, and SO2 that enters the stratosphere helps reflect solar radiation away leading to cooling. Silicate minerals in rocks are attacked by hydrogen ions (H+) produced by the solution of CO2 in rain water to form a weak acid (H2CO3: carbonic acid). A very simple example of such chemical weathering is the breakdown of calcium silicate:

CaSiO3  +  2CO2  + 3H2O  =  Ca2+  +  2HCO3–  +  H4SiO4  

The reaction results in calcium and bicarbonate ions being dissolved in water, eventually to enter the oceans where they are recombined in the shells of planktonic organisms as calcium carbonate. On death, their shells sink and end up in ocean-floor sediments along with unoxidised organic carbon compounds. The net result of this part of the carbon cycle is reduction in atmospheric CO2 and a decreased greenhouse effect: increased silicate weathering cools down the climate. Overall, internal processes – particularly volcanism – and surface processes – weathering and carbonate burial – interact. During the ‘boring billion’ they seem to have been in balance. The two processes lie at the core of attempts to model global climate behaviour in the past, along with what is known about developments in plate tectonics – continental break-up, seafloor spreading and orogenies – and large igneous events resulting from mantle plumes. A group of geoscientists from the Universities of Sydney and Adelaide, Australia have evaluated the tectonic factors that may have contributed to the first and longest Snowball Earth of the Neoproterozoic: the Sturtian glaciation (717 to 661 Ma) (Dutkiewicz, A. et al. 2024. Duration of Sturtian “Snowball Earth” glaciation linked to exceptionally low mid-ocean ridge outgassing. Geology, v. 52, online early publication; DOI: 10.1130/G51669.1).

Palaeogeographic reconstructions (Robinson projection) during the early part of the Sturtian global glaciation: LEFT based on geological data from Neoproterozoic terrains on modern continents; RIGHT based on palaeomagnetic pole positions from those terrains. Acronyms refer to each terrains, e.g. Am is Amazonia, WAC is the West African Craton. Orange lines are ocean ridges, those with teeth are subduction zone. (Credit: Dutkiewicz et al., parts of Fig. 1)

Shortly before the Sturtian began there was a major flood volcanism event, forming the Franklin large igneous province, remains of which are in Arctic Canada. The Franklin LIP is a subject of interest for triggering the Sturtian, by way of a ‘volcanic winter’ effect from SO2 emissions or as a sink for CO2­ through its weathering. But both can be ruled out as no subsequent LIP is associated with global cooling and the later, equally intense Marinoan global glaciation (655 to 632 Ma) was bereft of a preceding LIP. Moreover, a world of growing frigidity probably could not sustain the degree of chemical weathering to launch a massive depletion in atmospheric CO2. In search of an alternative, Adriana Dutkiewicz and colleagues turned to the plate movements of the early Neoproterozoic. Since 2020 there have been two notable developments in modelling global tectonics of that time, which was dominated by the evolution of the Rodinia supercontinent. One is based largely on geological data from the surviving remnants of Rodinia (download animation), the other uses palaeomagnetic pole positions to fix their relative positions: the results are very different (download animation).

Variations in ocean ridge lengths, spreading rates and oceanic crust production during the Neoproterozoic estimated from the geological (orange) and palaeomagnetic (blue) models. Credit: Dutkiewicz et al., parts of Fig. 2)

The geology-based model has Rodinia beginning to break up around 800 Ma ago with a lengthening of global constructive plate margins during disassembly. The resulting continental drift involved an increase in the rate of oceanic crust formation from 3.5 to 5.0 km2 yr-1. Around 760 Ma new crust production more than halved and continued at a much slowed rate throughout the Cryogenian and the early part of the Ediacaran Period.  The palaeomagnetic model delays breakup of the Rodinia supercontinent until 750 Ma, and instead of the rate of crust production declining through the Cryogenian it more than doubles and remains higher than in the geological model until the late Ediacaran. The production of new oceanic crust is likely to govern the rate at which CO2 is out-gassed from the mantle to the atmosphere. The geology-based model suggests that from 750 to 580 Ma annual CO2 additions could have been significantly below what occurred during the Pleistocene ice ages since 2.5 Ma ago. Taking into account the lower solar heat emission, such a drop is a plausible explanation for the recurrent Snowball Earths of the Neoproterozoic. On the other hand, the model based on palaeomagnetic data suggests significant warming during the Cryogenian contrary to a mass of geological evidence for the opposite.

A prolonged decrease in tectonic activity thus seems to be a plausible trigger for global glaciation. Moreover, reconstruction of Precambrian global tectonics using available palaeomagnetic data seems to be flawed, perhaps fatally. One may ask, given the trends in tectonic data: How did the Earth repeatedly emerge from Snowball episodes? The authors suggest that the slowing or shut-down of silicate weathering during glaciations allowed atmospheric CO2 to gradually build up as a result of on-land volcanism associated with subduction zones that are a quintessential part of any tectonic scenario.

This kind of explanation for recovery of a planet and its biosphere locked in glaciation is in fact not new. From the outset of the Snowball Earth hypothesis much the same escape mechanisms were speculated and endlessly discussed. Adriana Dutkiewicz and colleagues have fleshed out such ideas quite nicely, stressing a central role for tectonics. But the glaring disparities between the two models show that geoscientists remain ‘not quite there’. For one thing, carbon isotope data from the Cryogenian and Ediacaran Periods went haywire: living processes almost certainly played a major role in the Neoproterozoic climatic dialectic.

Neanderthals and the earliest ‘plastic’ handles

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February 2024 was a notable month for discoveries about ancient technology: first that of an ancient tool probably used in rope making and now signs of the use of a composite ‘plastic’ material in stone-tool hafts. Both are from Neanderthal sites in France, the first dated around 52 to 41 ka and the second in the Le Moustier rock shelters of the Dordogne – the type locality for the Mousterian culture associated with Neanderthals (Schmidt, P. et al. 2024. Ochre-based compound adhesives at the Mousterian type-site document complex cognition and high investment. Science Advances, v. 10, article ead10822; DOI: 10.1126/sciadv.adl0822), dated at around 56 to 40 ka. The second discovery resulted from the first detailed analysis of unstudied artifacts unearthed from Le Moustier in 1907 by Swiss archaeologist Otto Hauser that had been tucked away in a Berlin Museum.

Patrick Schmidt of the University of Tubingen in Germany and colleagues  from Germany, the US and Kazakhstan identified stone artifacts that show traces of red and yellow colorants. At first sight it could be suggested that they are decorations of some kind. However, they coat only parts of the stone flakes and are sharply distinct from the fresh rock surface and the sharpest edges. Another feature discovered during chemical analysis is that the colour is due to iron hydroxides (goethite) but this ochre is mixed with natural bitumen: the coating is a composite of an adhesive and filler not far different from what can be purchased in any hardware store.

LEFT: Stone flake from the Le Moustier site in France, partly coated with a reddish iron-rich colorant. RIGHT: Experimental stone flakes with 55:44 mix of goethite and bitumen (top) and pure bitumen (bottom) being handled. (Credit: Schmidt et al. Figs 1A, 3).

The authors tested the properties of the mixtures against those of bitumen alone – an adhesive known to have been used along with various tree resins to haft blades to spears in earlier times. In particular they examined the results of ‘cooking’ the substances. Whether unheated or ‘cooked’ a mixture of ochre and bitumen is up to three times stronger than pure bitumen. A further advantage is that the mixed ingredients are not sticky when cooked and cooled, whereas bitumen remains sticky, as the illustration clearly shows. Anyone who has handled a stone blade realises how sharp they are, and not just around the cutting edges. So Schmidt and colleagues tried to use the composite material as a protective handle when stone flake tools were gripped for cutting or carving. The composite handles worked well on scrapers and blades, even in the softer, ‘uncooked’ form

Similar composite adhesives are known from older sites in Africa associated with anatomically modern humans, but not for this particular, very practical use. It is perhaps possible that the use of bitumen mixed with ochre was brought into Europe by AMH migrants and adopted by Neanderthals who came into contact with them. Yet the limestones of the Dordogne valley yield both bitumen in liquid and solid forms, and ochers are easily found because of their striking colours. Long exposure of petroleum seeps drives off lighter petroleum compounds to leave solid residues that can be melted easily to tarry consistency. So there is every reason to believe that Neanderthals developed this technology unaided. As Schmidt has commented, “Compound adhesives are considered to be among the first expressions of the modern cognitive processes that are still active today”.

Changing Atlantic Ocean currents may threaten Gulf Stream warming of Europe

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Climate during the last Ice Age was continually erratic. Generally fine-grained muds cored from the floor of the North Atlantic Ocean show repeated occurrences of layers containing gravelly debris. These have been ascribed to periods when ice sheets on Greenland and Scandinavia calved icebergs at an exceptionally fast rate, to release coarse debris as they melted while drifting to lower latitudes. These ‘iceberg armadas’ (known as Heinrich events) left their unmistakable signs as far south as Portugal. Their timing correlates with short-lived (1 to 2 ka) warming-cooling episodes (Dansgaard-Oeschger events) recorded in Greenland ice cores that involved variations in air temperature of up to 15°C. The process that resulted in these sudden climate shifts seems to have been changing ocean circulation brought about by vast amounts of fresh water flooding into the Arctic and North Atlantic Oceans. This lowered seawater density to the extent that its upper parts could not sink when cooled. It is this thermohaline circulation that drags warmer surface water northwards, known as the Atlantic Meridional Overturning Circulation (AMOC), part of which is the Gulf Stream. When it fails or slows the result is plummeting temperatures at high latitudes. The last major AMOC shutdown was after 8 ka of warming that followed the last glacial maximum. Between 12.9 and 11.7 ka major glaciers grew again north of about 50°N in the period known as the Younger Dryas, almost certainly in the aftermath of a flood to the Arctic Ocean of glacial meltwater from the Canadian Shield. Around 8.2 thousand years ago human re-colonisation of Northern Europe was set back by a similar but lesser cooling event.

The Atlantic Meridional Overturning Circulation (AMOC). Red – warm surface currents; cyan – cold deep-water flow. (Credit: Stefano Crivellari)

Three researchers at Utrecht University, the Netherlands have issued an early warning that the AMOC may have reached a critical condition (Van Westen, R.M., Kliphuis, M & Dijkstra, H.A. 2024. Physics-based early warning signal shows that AMOC is on tipping course. Science Advances, v. 10, article adl1189; DOI: 10.1126/sciadv.adk1189). Previous modelling of AMOC has suggested that only rapid, massive decreases in the salinity of North Atlantic surface water near the Arctic Circle could shut down the Gulf Stream in the manner of Younger Dryas and Dansgaard-Oeschger events. René van Westen and colleagues have simulated the effects of steady, long-term addition of fresh water from melting of the Greenland ice sheet. They ran a sophisticated Earth System model for six months on the Netherlands’ Snellius super computer. Their model used a slowly increasing influx of glacial meltwater to the Atlantic at high northern latitudes.

The various feedbacks in the model eventually shut down the AMOC, predicted to result in cooling of NW Europe by 10 to 15 °C in a matter of a few decades. Yet to achieve that required the model to simulate more than 2000 years of change. It took 1760 years for a persistent AMOC transport of 10 to 15 million m3 s-1 to drop over a century or so and reach near-zero. That collapse involved around 80 times more melting of Greenland’s ice sheet than at present. Yet their modelling does not take into account global warming: including that factor would have exceeded their budgeted supercomputer time by a long way. Melting of the Greenland ice sheet is, however, accelerating dramatically

Van Westen et al. have shown the possibility that steadily increasing ice-sheet melting can, theoretically, ’flip’  the huge current system associated with the Atlantic Ocean, and with it regional climate patterns. The tangible fear today is of a more than 1.5°C increase in global surface temperature, yet a warming-induced failure of AMOC may cause local annual temperatures to fall by up to ten times that. Rather than the currently heralded disappearance of sea-ice from the Arctic Ocean, it may spread in winter to as far south as the North Sea. The only way of forecasting in detail what may actually happen – and where – is ever-more sophisticated and costly modelling of ocean currents and ice melting in a warming world. Uncertain as it stands, the work by van Westen and colleagues may well be ignored: perhaps as a ‘thing we dinnae care to speak aboot’.

See also: Le Page, M. 2024. Atlantic current shutdown is a real danger, suggests simulation. New Scientist, 9 February 2024; Watts, J. 2024. Atlantic Ocean circulation nearing ‘devastating’ tipping point, study finds. The Guardian, 9 February 2024.

Earliest evidence for rope making: a sophisticated tool

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Even at my age, if I rummage through pockets of various bits of outdoor clothing there’s a good chance I’ll find a handy length of string that I have scavenged at some time. It’s a just-in-case thing, which I learned from my father and grandad. One can hardly imagine a hunter-gatherer not having string or lengths of sinew for that very reason. Cordage has many other uses than merely securing something: bags, mats, nets, snares, fabric, baskets, huts made of sticks and fronds, and even watercraft. Yet archaeological evidence for twine is exceedingly rare. The oldest known string – made of bark fibres – was found wrapped around a stone tool at a 52 to 41 ka Neanderthal site in the Rhône valley 120 km north-west of Marseille. Rope is somewhat more difficult to make as it requires twisting together several lengths of simpler cordage. Once that skill is cracked a rope maker is on the verge of engineering!

The reassembled rope-making tool from Hohle Fels Cave (Credit: Conard & Rots, Fig 2)

In 2015 archaeologists unearthed several pieces of worked mammoth ivory from the Hohle Fels Cave in SW Germany. They were dated to between 40 to 35 ka and associated with Aurignacian stone tools made by modern humans. Fifteen pieces could be fitted together to yield a 20 cm long ‘baton’. First believed to be some kind of ritual object, the fact that 4 circular holes had been bored through the ‘baton’ suggested it must have had some practical use, perhaps for straightening wooden shafts. Then it became clear that each hole was surrounded by spirals of carefully carved, V-shaped notches. Nicholas Conard and Veerle Rots of the University of Tubingen realised that the object may have been used for making rope using a technique known from the Egyptian pharaonic period into medieval times (Conard, N.J. & Rots, V. 2024. Rope making in the Aurignacian of Central Europe more than 35,000 years ago. Science Advances, v. 10, article adh5217; DOI: 10.1126/sciadv.adh5217).

Frame from a movie showing how the tool may have been used to make ropes. The three ‘feeders’ twist foliage clockwise whereas the fourth pulls and imparts an anticlockwise twist to the three stands. (Credit: Conard & Rots, Supplementary material, Fig S15)

After a little practice, four people were able to make sturdy rope using a replica of the tool. Three twisted together fibrous materials, such as the stems and leaves of bulrushes (Typha), and pushed the rough cordage through the intact holes. A fourth person pulled the cordage through and counter-twisted the three strands into rope about 1.5 cm thick – thicker rope would also have required a tool with more holes and more operators. The spiral grooves maintained the initial clockwise rotation of each strand of cordage, so that when all three were twisted together in an anticlockwise sense the counter rotation held the rope together firmly. Remarkably, the small team were able to produce 5 m of rope in 10 minutes. Other common kinds of fibrous plant material, such as linden and willow were used successfully. Incidentally, the tool squeezed edible starch from the foliage of bulrushes. But it seems that this particular rope-making took only performed well for coarse materials. Making rope from finer firbres, such as animal sinew, nettle, flax and hemp would probably have required another design with smaller holes.

A movie of the manufacturing process can be downloaded.

An astronomical background to flood basalt events and mass extinctions?

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Michael Rampino and Ken Caldeira of New York University and the Carnegie Institute have for at least three decades been at the forefront of studies into mass extinctions and their possible causes, including flood-basalt volcanism, extraterrestrial impacts and climate change. As early as 1993 the duo reported an ubiquitous 26-million year cycle in plate tectonic and volcanic activity. In Rampino’s 2017 book Cataclysms: A New Geology for the Twenty-First Century the notion of a process similar to Milutin Milankovich’s prediction of Earth’s orbital characteristics underpinning climate cyclicity figured in his thinking (see Shock and Er … wait a minute, Earth-logs, October 2017). Rampino postulated then that this longer-term geological cyclicity could be linked to gravitational changes during the Solar System’s progress around the Milky Way galaxy. He was by no means the first to turn to galactic forces, Johann Steiner having made a similar suggestion in 1966. The notion stems from the Solar System’s wobbling path as it orbits the centre of the Milky Way galaxy about every 250 Ma, which may result in its passage through a vast layered variation in several physical properties aligned at right angles to galactic orbital motions. This grand astronomical theory is ‘a story that will run and run’; and it has. It is possible that the galaxy has corralled dark matter in a disc within the galactic plane, which Rampino and Caldeira latched onto that notion a year after it appeared in Physical Review Letters in 2014.

Map of the Milky Way galaxy as it would appear from a viewpoint above the galactic centre. The Solar System is located in the Orion Spur (green dot) (Credit: Wikipedia)

As I commented in my brief review of Rampino’s book: “As for Rampino’s galactic hypothesis, the statistics are decidedly dodgy, but chasing down more forensics is definitely on the cards.” Indeed they have been chased in a recent review by the pair and their colleague Sedelia Rodriguez (Rampino, M.R., Caldeira, K. & Rodriguez, S. 2023. Cycles of ∼32.5 My and ∼26.2 My in correlated episodes of continental flood basalts (CFBs), hyper-thermal climate pulses, anoxic oceans, and mass extinctions over the last 260 My: Connections between geological and astronomical cycles. Earth-Science Reviews, v. 246 ; DOI: 10.1016/j.earscirev.2023.104548; reprint available on request from Rampino). They base their amplified case on much more than radiometric dates of continental flood basalt (CFB) events matched against the stratigraphic record of biotic diversity. Among the proxies are published measurements of mercury and osmium isotope anomalies in oceanic sediments that are best explained by sudden increases in basaltic magma eruption; signs of deep ocean anoxia; new dating of marine and non-marine extinctions in the fossil record, and episodes of sudden extreme climatic heating.

Statistical analysis of the ages of anoxic events and marine extinctions has yielded cycles of 32.5 and 26.2 Ma, those for CFBs having a 32.8 Ma periodicity. A note of caution, however: their data only cover the last 266 Ma – about one orbit of the solar system around the galactic centre. The authors attribute their interpretation of the cycles “to the Earth’s tectonic-volcanic rhythms, but the similarities with known Milankovitch Earth orbital periods and their amplitude modulations, and with known Galactic cycles, suggest that, contrary to conventional wisdom, the geological events and cycles may be paced by astronomical factors”.

Whether or not a detailed record of appropriate proxies can be extended back beyond the Late Permian, remains to be seen. The main fly-in-the-ointment is the tendency of CFB provinces to form high ground so that they are readily eroded away. Pre-Mesozoic signs of their former presence lie in basaltic dyke swarms that cut through older  crystalline continental crust. The marine sedimentary record is somewhat better preserved. A search for distinctive anomalies in osmium isotopes and mercury concentrations, which are useful proxies for global productivity of basaltic magmas, will be costly. Moreover, dating will depend to a large degree on the traditional palaeontology of strata, which in Palaeozoic rocks is more difficult to calibrate precisely by absolute radiometric dating.