Category: Miscellaneous commentary

Provenance of the Stonehenge Altar Stone: a puzzling development

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 Curiously, two weeks after my previous post about Stonehenge, a wider geochemical study of the Devonian sandstones and a number of Neolithic megaliths in Orkney seems to have ruled out the Stonehenge Altar Stone having been transported from there (Bevins, R.E. et al. 2024. Was the Stonehenge Altar Stone from Orkney? Investigating the mineralogy and geochemistry of Orcadian Old Red sandstones and Neolithic circle monuments. Journal of Archaeological Science: Reports, v. 58, article 104738;   DOI: 10.1016/j.jasrep.2024.104738). Since two of the authors of Clarke et al. (2024) were involved in the newly published study, it is puzzling at first sight why no mention was made in that paper of the newer results. The fact that the topic is, arguably, the most famous prehistoric site in the world may have generated a visceral need for getting an academic scoop, only for it to be dampened a fortnight later. In other words, was there too much of a rush?

The manuscript for Clarke et al. (2024) was received by Nature in December 2023 and accepted for publication on 3 June 2024; a six-month turnaround and plenty of time for peer review. On the other hand, Bevins et al. (2024) was received by the Journal of Archaeological Science on 23 July 2024, accepted a month later and then hit the website a week after that: near light speed in academic publishing. And it does not refer to the earlier paper at all, despite two of its authors’ having contributed to it. Clarke et al. (2024) was ‘in press’ before Bevins et al. (2024) had even hit the editor’s desk. The work that culminated in both papers was done in the UK, Australia, Canada and Sweden, with some potential for poor communication within the two teams. Whatever, the first paper dangled the carrot that Orkney might have been the Altar Stone’s source, on the basis of geochemical evidence that the grains that make up the sandstone could not have been derived from Wales but were from the crystalline basement of NE Scotland. The second shows that this ‘most popular’ Scottish source may be ruled out. To Orcadians and the archaeologists who worked there, long in the shade of vast outpourings from Salisbury Plain, this might come as a great disappointment.

Cyclical sediments of the Devonian Stromness Flagstones. (Credit Mike Norton, Wikimedia)

The latest paper examines 13 samples from 8 outcrops of the Middle Devonian Stromness Flagstones strata in the south of the main island of Orkney close to the Ring of Brodgar and the Stones of Stenness, and the individual monoliths in each. On the main island, however, there is a 500 m sequence of Stromness Flagstones in which can be seen 50 cycles of sedimentation. Each cycle contains sandstone beds of various thicknesses and textures. They are fluviatile, lacustrine or aeolian in origin. So the Neolithic builders of Orkney had a wide choice, depending on where they erected monumental structures. Almost certainly they chose monolithic stones where they were most easy to find: close to the coast where exposure can be 100 %. The Ring of Brodgar and the Stones of Stenness are not on the coast, so the enormous stones would have to be dragged there. There is an ancient pile of stones (Vestra Fiold) about 20 km to the NW where some of the mmegaliths may have been extracted, but ancient Orcadians would have been spoilt for choice if they had their hearts set on erecting monoliths!

In a nutshell, the geological case made by Bevins et al. (2024) for rejecting Orkney as the source for the Stonehenge Altar Stone (AS) is as follows: 1. Grains of the mineral baryte (BaSO4­) present in the AS are only found in two of the Orkney rock samples. 2. All the Orcadian sandstone samples contain lots of grains of K-feldspar (KAlSi3O8) – common in the basement rocks of northern Scotland – but the AS contains very little. 3. A particular clay mineral (tosudite) is plentiful in the AS, but was not detected in the rock samples from Orkney. Does that rule out a source in Orkney altogether? Well, no: only the outcrops and megalith samples involved in the study are rejected.

To definitely negate an Orcadian source would require a monumental geochemical and mineralogical study across Orkney; covering every sedimentary cycle. Searching the rest of the Old Red Sandstone elsewhere in NE Scotland – and there is a lot of it – would be even more likely to be fruitless. Tracking down the source for the basaltic bluestones at Stonehenge was easy by comparison, because they crystallised from a particular magma over a narrow time span and underwent a specific degree of later metamorphism. They were easily matched visually and under the microscope with outcrops in West Wales in the 1920s and later by geochemical features common to both.

But all that does not detract from the greater importance of the earlier paper (Clarke et al., 2024), which enhanced the idea of Neolithic cultural coherence and cooperation across the whole of Britain. The building of Stonehenge drew people from the far north of Scotland together with those of what are now Wales and England. Since then it hasn’t always been such an amicable relationship …

See also:  Addley, E. 2024. Stonehenge tale gets ‘weirder’ as Orkney is ruled out as altar stone origin. The Guardian 5 September 2024.

Geology cracks Stonehenge mysteries

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High resolution vertical aerial photograph of Stonehenge. (Credit: Gavin Hellier/robertharding/Getty)

During the later parts of the Neolithic the archipelago now known as the British Isles and Ireland was a landscape on which large stone buildings with ritual and astronomical uses were richly scattered. The early British agricultural societies also built innumerable monuments beneath which people of the time were buried, presumably so that they remained in popular memory as revered ancestors. Best known among these constructions is the circular Stonehenge complex of dressed megaliths set in the riot of earlier, contemporary and later human-crafted features of the Chalk downs known as Salisbury Plain. Stonehenge itself is now known to have been first constructed some five thousand years ago (~3000 BCE) as an enclosure surrounded by a circular ditch and bank, together with what seems to have been a circular wooden palisade. This was repeatedly modified during the following two millennia. Around 2600 BCE the wooden circle was replaced by one of stone pillars, each weighing about 2 t. These ‘bluestones’ are of mainly basaltic igneous origin unknown in the Stonehenge area itself. The iconic circle of huge, 4 m monoliths linked by 3 m lintel stones that enclose five even larger trilithons arranged in a horseshoe dates to the following two-centuries to 2400 BCE coinciding with the Early Bronze Age when newcomers from mainland Europe – perhaps as far away as the steppe of western Russia – began to replace or assimilate the local farming communities. This phase included several major modifications of the earlier bluestones.

It might seem that the penchant for circular monuments began with the Neolithic people of Salisbury Plain, and then spread far and wide across the archipelago in a variety of sizes. However, it seems that building of sophisticated monuments, including stone circles, began some two centuries earlier than in southern England in the Orkney Islands 750 km further north and, even more remote, in the Outer Hebrides of Scotland. A variety of archaeological and geochemical evidence, such as the isotopic composition of the bones of livestock brought to the vicinity of Stonehenge during its period of development and use, strongly suggests that people from far afield participated. Remarkably, a macehead made of gneiss from the Outer Hebrides turned up in an early Stonehenge cremation burial. Ideas can only have spread during the Neolithic through the spoken word. As it happens, the very stones themselves came from far afield. The earliest set into the circular structure, the much tinkered-with bluestones, were recognised to be exotic over a century ago. They match late Precambrian dolerites exposed in western Wales, first confirmed in the 1980s through detailed geochemical analyses by the late Richard Thorpe and his wife Olwen Williams-Thorpe of the Open University. Some suggested that they had been glacially transported to Salisbury Plain, despite complete lack of any geological evidence. Subsequently their exact source in the Preseli Hills was found, including a breakage in the quarry that exactly matched the base of one of the Stonehenge bluestones. They had been transported 230 km to the east by Neolithic people, using perhaps several means of transport. The gigantic monoliths, made of ‘sarsen’ – a form of silica-cemented sandy soil or silcrete – were sourced from some 25 km away where Salisbury Plain is still liberally scattered with them. Until recently, that seemed to be that as regards provenance, apart from a flat, 5 x 1 m slab of sandstone weighing about 6 t that two fallen trilithon pillars had partly hidden. At the very centre of the complex, this had been dubbed the ‘Altar Stone’, originally supposed to have been brought with the bluestones from west Wales.

The stones of Stonehenge colour-coded by lithology. The sandstone ‘Altar Stone’ lies beneath fallen blocks of a trilithon at the centre of the circle. (Credit: Clarke et al. 2024, Fig 1a)

A group of geologists from Australia and the UK, some of whom have long been engaged with Stonehenge, recently decided to apply sophisticated geochemistry at two fragments broken from the Altar Stone, presumably when the trilithons fell on it (Clarke, A. J. I. et al.2024.  A Scottish provenance for the Altar Stone of Stonehenge. Nature v.632, p. 570–575; DOI: 10.1038/s41586-024-07652-1). In particular they examined various isotopes and trace-elements in sedimentary grains of zircon, apatite and rutile that weathering of igneous rocks had contributed to the sandstone, along with quartz, feldspar, micas and clay minerals. It turned out that the zircon grains had been derived from Mesoproterozoic and Archaean sources beneath the depositional site of the sediment (the basement). The apatite and rutile grains show clear signs of derivation from 460 Ma old (mid-Ordovician) granites. The basement beneath west Wales is by no stretch of the imagination a repository of any such geology. That of northern Scotland certainly does have such components, and it also has sedimentary rocks derived from such sources: the Devonian of Orkney and mainland Scotland surrounding the Moray Firth. Unlike the lithologically unique bluestones, the sandstone is from a thick and widespread sequence of terrestrial sediments colloquially known as the ‘Old Red Sandstone’. The ORS of NE Scotland was deposited mainly during the Devonian Period (419 to 369 Ma) as a cyclical sequence in a vast, intermontane lake basin. Much the same kinds of rock occur throughout the sequence, so it is unlikely that the actual site where the ‘Alter Stone’ was selected will ever be known.

To get the ‘Alter Stone’ (if indeed that is what it once was) to Stonehenge demanded transport from its source over a far more rugged route, three times longer than the journey that brought the bluestones from west Wales: at least 750 km. It would probably have been dragged overland. Many Neolithic experts believe that transport of such a large block by boat is highly unlikely; it could easily have been lost at sea and, perhaps more important, few would have seen it. An overland route, however arduous, would have drawn the attention of everyone en route, some of whom might have been given the honour of helping drag such a burden for part of the way. The procession would certainly have aroused great interest across the full extent of Britain. Its organisers must have known its destination and what it signified, and the task would have demanded fervent commitment. In many respects it would have been a project that deeply unified most of the population. That could explain why people from near and far visited the Stonehenge site, herding livestock for communal feasting on arrival. Evidence is now pointing to the construction and use of the ritual landscape of Salisbury Plain as an all-encompassing joint venture of most of Neolithic Britain’s population. It would come as no surprise if objects whose provenance is even further afield come to light. It remained in use and was repeatedly modified during the succeeding Bronze Age up to 1600 BCE. By that time, the genetic group whose idea it was had been assimilated, so that only traces of its DNA remain in modern British people. This seems to have resulted from waves of immigrants from Central Europe, the Yamnaya, who brought new technology and the use of metals and horses.

See also: Gaind, N. & Smith, R. 2024. Stonehenge’s enigmatic centre stone was hauled 800 kilometres from Scotland. Nature, v. 632, p. 484-485; DOI: 10.1038/d41586-024-02584-2; Addley, E. 2024. Stonehenge megalith came from Scotland, not Wales, ‘jaw-dropping’ study finds. The Guardian, 14 August 2024.

The gross uncertainty of climate tipping points

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That the Earth has undergone sudden large changes is demonstrated by all manner of geoscientific records. It seems that many of these catastrophic events occurred whenever steady changes reach thresholds that trigger new behaviours in the interlinked atmosphere, hydrosphere, atmosphere, biosphere and lithosphere that constitute the Earth system. The driving forces for change, both steady and chaotic, may be extra-terrestrial, such as the Milankovich cycles and asteroid impacts, due to Earth processes themselves or a mixture of the two. Our home world is and always has been supremely complicated; the more obviously so as knowledge advances.  Abrupt transitions in components of the Earth system occur when a critical forcing threshold is passed, creating a ‘tipping point’. Examples in the geologically short term are ice-sheet instability, the drying of the Sahara, collapse of tropical rain forest in the Amazon Basin, but perhaps the most important is the poleward transfer of heat in the North Atlantic Ocean. That is technically known as the Atlantic Meridional Overturning Circulation with the ominous acronym AMOC.

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

As things stand today, warm Atlantic surface water, made more saline and dense by evaporation in the tropics is transferred northwards by the Gulf Stream. Its cooling at high latitudes further increases the density of this water, so at low temperatures it sinks to flow southwards at depth. This thermohaline circulation continually pulls surface water northwards to create the AMOC, thereby making north-western European winters a lot warmer than they would be otherwise. Data from Greenland ice cores show that during the climatic downturn to the last glacial maximum, the cooling trend was repeatedly interrupted by sudden warming-cooling episodes, known as Dansgaard-Oeschger events, one aspect of which was the launching of “armadas” of icebergs to latitudes as far south as Portugal (known as Heinrich events), which left their mark as occasional gravel layers in the otherwise muddy sediments on the deep Atlantic floor (see: Review of thermohaline circulation; February 2002).

These episodes involved temperature changes over the Greenland icecap of as much as 15°C.  They began with warming on this scale within a matter of decades followed by slow cooling to minimal temperatures, before the next turn-over. Various lines of evidence suggest that these events were accompanied by shutdowns of AMOC and hence the Gulf Stream, as shown by variations in the foraminifera species in sea-floor sediments. The culprit was vast amounts of fresh water pouring into the Arctic and northernmost Atlantic Oceans, decreasing the salinity and density of the surface ocean water. In these cases that may have been connected to repeated collapse of circumpolar ice sheets to launch Heinrich’s iceberg armadas. A similar scenario has been proposed for the millennium-long Younger Dryas cold spell that interrupted the onset of interglacial conditions. In that case the freshening of high-latitude surface water was probably a result of floods released when glacial barriers holding back vast lakes on the Canadian Shield burst.

At present the Greenland icecap is melting rapidly. Rising sea level may undermine the ice sheet’s coastal edges causing it to surge seawards and launch an iceberg armada. This may be critical for AMOC and the continuance of the Gulf Stream, as predicted by modelling: counter-intuitive to the fears of global warming, at least for NW Europe. In August 2024 scientists from Germany and the UK published what amounts to a major caution about attempts to model future catastrophes of this kind (Ben-Yami, M. et al 2024, Uncertainties too large to predict tipping times of major Earth system components from historical data, Science Advances, v. 10, article  eadl4841; DOI 10.1126/sciadv.adl4841). They focus on records of the AMOC system, for which an earlier modelling study predicted that a collapse could occur between 2025 and 2095: of more concern than global warming beyond the 1.5° C currently predicted by greenhouse-gas climate models .

Maya Ben-Yami and colleagues point out that the assumptions about mechanisms in Earth-system modelling and possible social actions to mitigate sudden change are simplistic.  Moreover, models used for forecasting rely on historical data sets that are sparse and incomplete and depend on proxies for actual variables, such as sea-surface and air temperatures. The further back in geological time, the more limited the data are. The authors assess in detail data sets and modelling algorithms that bear on AMOC. Rather than a chance of AMOC collapse in the 21st century, as suggested by others, Ben Yami et al. reckon that any such event  lies between 2055 and 8065 CE, which begs the question, “Is such forecasting  worth the effort?”, however appealing it might seem to the academics engaged in climatology. The celebrated British Met Office and other meteorological institutions, use enormous amounts of data, the fastest computers and among the most powerful algorithms on the planet to simulate weather conditions in the very near future. They openly admit a limit on accurate forecasting of no more than 7 day ahead. ‘Weather’ can be regarded as short-term climate change.

It is impossible to stop scientists being curious and playing sophisticated computer games with whatever data they have to hand. Yet, while it is wise to take climate predictions with a pinch of salt because of their gross limitations, the lessons of the geological past do demand attention. AMOC has shut down in the past – the last being during the Younger Dryas – and it will do so again. Greenhouse global warming probably increases the risk of such planetary hiccups, as may other recent anthropogenic changes in the Earth system. The most productive course of action is to reduce and, where possible, reverse those changes. In my honest opinion, our best bet is swiftly to rid ourselves of an economic system that in the couple of centuries since the ‘Industrial Revolution’ has wrought these unnatural distortions.

Tectonic history and the Drake Equation

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In 1961 ten scientists interested in a search for extra-terrestrial intelligence met at Green Bank, West Virginia, USA, none of whom were geologists or palaeontologists. The participants called themselves “The Order of the Dolphin”, inspired by the thorny challenge of discovering how small cetaceans communicated: still something of a mystery. To set the ball rolling, Frank Drake an American astrophysicist and astrobiologist, proposed an algorithm aimed at forecasting the number of planets elsewhere in our galaxy on which ‘active, communicative civilisations’ (ACCs) might live. The Drake Equation is formulated as:

ACCs = R* · fp · ne · fl · fi · fc · L

where R* = number of new stars formed per year, fp = the fraction of stars with planetary systems, ne = the average number of planets that could support life (habitable planets) per planetary system, fl = the fraction of habitable  planets that develop primitive life, fi = the fraction of planets with life that evolve intelligent life and civilizations, fc = the fraction of civilizations that become ACCs, L = the length of time that ACCs broadcast radio into space. A team of then renowned scientists from several disciplines discussed what numbers to attach to these parameters. Their ‘educated guesses’ were: R* – one star per year; fp – one fifth to one half of all stars will have planets; ne – 1 to 5 planets per planetary system will be habitable; of which 100% will develop life (fl) and 100% (fi) will eventually develop intelligent life and civilisations; of those civilisations 10 to 20 % (fc) will eventually develop radio communications; which will survive for between a thousand years and 100 Ma (L). Acknowledging the great uncertainties in all the parameters, Drake inferred that between 103 and 108 ACCs exist today in the Milky Way, which is ~100 light years across and contains 1 to 4 x 1011 stars).

Today the values attached to the parameters and the outcomes seem absurdly optimistic to most people, simply because, despite 4 decades of searching by SETI there have been no signs of intelligible radio broadcasts from anywhere other than Earth and space probes launched from here. This is humorously referred to as the Fermi Paradox. There are however many scientists who still believe that we are not alone in the galaxy, and several have suggested reasons why nothing has yet been heard from ACCs. Robert Stern of the University of Texas (Dallas), USA and Taras Gerya of ETH-Zurich, Switzerland have sought clues from the history of life on Earth and that of the inorganic systems from which it arose and in which it has evolved that bear on the lack of any corrigible signals in the 63 years since the Drake Equation (Stern, R.J & Gerya, T.V. 2024. The importance of continents, oceans and plate tectonics for the evolution of complex life: implications for finding extraterrestrial civilizations. Nature (Scientific Reports), v. 14, article 8552; DOI: 10.1038/s41598-024-54700-x – definitely worth reading). Of course, Stern and Gerya too are fascinated by the scientific question as to whether or not there are ‘active, communicative civilisations’ elsewhere in the cosmos. Their starting point is that the Drake Equation is either missing some salient parameters, or that those it includes are assigned grossly optimistic magnitudes.

Life seems to have been present on Earth 3.8 Ga ago but multicelled animals probably arose only in the Late Neoproterozoic since 1.0 Ga ago. So here it has taken a billion years for their evolution to achieve terrestrial ACC-hood. Stern and Gerya address what processes favour life and its rapid evolution. Primarily, life depends on abundant liquid water: i.e. on a planet within the ‘Goldilocks Zone’ around a star. The authors assume a high supply of bioactive compounds – organic carbon, ammonium, ferrous iron and phosphate to watery environments. Phosphorus is critical to their scenario building. It is most readily supplied by weathering of exposed continental crust, but demands continual exposure of fresh rock by erosion and river transport to maintain a steady supply to the oceans. Along with favourable climatic conditions, that can only be achieved by an oxidising environment that followed the Great Oxidation Event (2.4 to 2.1 Ga) and continual topographic rejuvenation by plate tectonics.

A variety of Earth-logs posts have discussed various kinds of evidence for the likely onset of plate tectonics, largely focussing on the Hadean and Archaean. Stern and Gerya prefer the Proterozoic Eon that preserves more strands of relevant evidence, from which sea-floor spreading, subduction and repeated collision orogenies can confidently be inferred. All three occur overwhelmingly in Neoproterozoic and Phanerozoic times. Geologists often refer to the whole of the Mesoproterozoic and back to about 2.0 Ga in the Palaeoproterozoic as the ‘Boring Billion’ during which carbon isotope data suggest very little change in the status of living processes: they were present but nothing dramatic happened after the Great Oxidation Event. ‘Hard-rock’ geology also reveals far less passive extensional events that indicate continental break-up and drift than occur after 1.0 Ga and to the present. It also includes a unique form of magmatism that formed rocks dominated by sodium-rich feldspar (anorthosites) and granites that crystallised from water-poor magmas. They are thought to represent build-ups of heat in the mantle unrelieved by plate-tectonic circulation. Before the ‘Boring Billion’ such evidence as there is does point to some kind of plate motions, if not in the modern style.

How different styles of tectonics influence living processes differently: a single stagnant ‘lid’ versus plate tectonics. (Credit: Stern and Gerya, Fig 2)

Stern and Gerya conclude that the ‘Boring Billion’ was dominated by relative stagnation in the form of lid tectonics.  They compare the influence of stagnant ‘lid’ tectonics on life and evolution with that of plate tectonics in terms of: bioactive element supply; oxygenation; climate control; habitat formation; environmental pressure (see figure). In each case single lid tectonics is likely to retard life and evolution, whereas plate tectonics stimulates them as it has done from the time of Snowball Earth and throughout the Phanerozoic. Only one out of 8 planets that orbit the sun displays plate tectonics and has both oceans and continents. Could habitable planets be a great deal rarer than Drake and his pals assumed? [look at exoplanets in Wikipedia] Whatever, Stern and Gerya suggest that the seemingly thwarted enthusiasm surrounding the Drake Equation needs to be tempered by the addition of two new terms: the fraction of habitable exoplanets with significant continents and oceans (foc)and the fraction of them that have experienced plate tectonics for at least half a billion years (fpt). They estimate foc to be on the order of 0.0002 to 0.01, and suggest a value for fpt of less than 0.17. Multiplied together yields value between less than 0.00003 and 0.002. Their incorporation in the Drake Equation drastically reduces the potential number of ACCs to between <0.006 and <100,000, i.e. to effectively none in the Milky Way galaxy rising to a still substantial number

There are several other reasons to reject such ‘ball-parking’ cum ‘back-of-the-envelope’ musings. For me the killer is that biological evolution can never be predicted in advance. What happened on our home world is that the origin and evolution of life have been bound up with the unique inorganic evolution of the Solar System and the Earth itself over more than 4.5 billion years. That ranges in magnitude from the early collision with another, Mars-sized world that reset the proto-Earth’s geochemistry and created a large moon whose gravity has cycled the oceans through tides and changed the length of the day continually for almost the whole of geological history. At least once, at the end of the Cretaceous Period, a moderately sized asteroid in unstable orbit almost wiped out life at an advanced stage in its evolution. During the last quarter billion years internally generated geological forcing mechanisms have repeatedly and seriously stressed the biosphere in roughly 36 Ma cycles (Boulila, S. et al. 2023. Earth’s interior dynamics drive marine fossil diversity cycles of tens of millions of years. Proceedings of the National Academy of Sciences, v. 120 article e2221149120; DOI: 10.1073/pnas.2221149120). Two outcomes were near catastrophic mass extinctions, at the ends of the Permian and Triassic Periods, from which life struggled to continue. As well as extinctions, such ‘own goals’ reset global ecosystems repeatedly to trigger evolutionary diversification based on the body plans of surviving organisms.

Such unique events have been going on for four billion years, including whatever triggered the Snowball Earth episodes that accompanied the Great Oxygenation Event around 2.4 Ga and returned to coincide with the rise of multicelled animals during the Cryogenian and Ediacaran Periods of the Late Neoproterozoic. For most of the Phanerozoic a background fibrillation of gravitational fields in the Solar System has occasionally resulted in profound cycling between climatic extremes and their attendant stresses on ecosystems and their occupants. The last of these coincided with the evolution of humanity: the only creator of an active, communicative civilisation of which we know anything. But it took four billion years of a host of diverse vagaries, both physical and biological to make such a highly unlikely event possible. That known history puts the Drake Equation firmly in its place as the creature of a bunch of self-publicising and regarding, ambitious academics who in 1961 basically knew ‘sweet FA’. I could go on … but the wealth of information in Stern and  Gerya’s work is surely fodder for a more pessimistic view of other civilisations in the cosmos.

Someone – I forget who – provided another, very practical reason underlying the lack of messages from afar. It is not a good idea to become known to all and sundry in the galaxy, for fear that others might come to exploit, enslave and/or harvest. Earth is still in a kind of  imperialist phase from which lessons could be drawn!

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.

Extreme scientific showing-off: Hominin fossils in space

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Good illustrations of self publicity and soaring ambition are the private space programmes of oligarchs Elon Musk (SpaceX), Jeff Bezos (Blue Origin) and Richard Branson (Virgin Galactic). For a cool US$65 million a ‘civilian’ can get a trip to the International Space Station on SpaceX; a one-hour suborbital flight on Blue Origin will cost US$300,000, with luck having Bezos as a companion; a reservation on Virgin Galactic for a 1 hour trip to the ‘edge of space’ (~100 km up) now costs US$624,000. It’s a tourist trip for the very, very rich only … but even the long-dead can go … or bits of them. On 8 September 2023 aboard Virgin Galactic flight Tim Nash, a South African billionaire had in his pocket a sturdy tube containing a thumb bone of Homo naledi and the collarbone of Australopithecus sediba. Nash reportedly said afterwards, “I am humbled and honoured to represent South Africa and all of humankind as I carry these precious representations of our collective ancestors”.

Reconstructed head of a somewhat annoyed Homo naledi. Credit: John Gurche, Mark Thiessen, National Geographic.

Nash was entrusted with these unique fossils by Lee Berger, Professor in Palaeoanthropology at Witwatersrand University, South Africa and a National Geographic Explorer-in-Residence. Berger recovered fossils of both species from limestone caves in the UNESCO World Heritage Site grandly named the Cradle of Humankind near Johannesburg. He is no stranger to controversy, and this venture cooked up with Nash seems to aim at promotion of South African achievements rather than having any scientific purpose. It has backfired spectacularly (see: McKie, R. 2023. ‘Callous, reckless, unethical’: scientists in row over rare fossils flown into space. The Observer, 22 October 2023). Comments from the anthropological world, six national and international bodies and perhaps the leading hominin specialist Professor Chris Stringer of the Natural History Museum in London include the words and phrases “callous”, “unethical”, “extraordinarily poorly thought-out”, “a publicity stunt”, “reckless” and “utterly irresponsible”. The caper breaks the South African, indeed international, scientific rule that fossils can only be allowed to travel for scientific purposes, applied consistently by similarly hominin-rich African countries such as Ethiopia, Kenya and Tanzania.

But, Hey, that’s how you get on in the world … isn’t it?

Plate tectonics loses another of its pioneers: W. Jason Morgan

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The theory of plate tectonics had a long gestation. Continental drift, one of its central tenets, was first proposed by the meteorologist Alfred Wegener in 1912. Apart from a few enthusiasts of such a dynamic aspect of geology, such as Alex du Toit and Arthur Holmes, the majority of geoscientists remained with the non-revolutionary fixist ideology of their Victorian predecessors. Wegener’s stumbling block was his proposed driving mechanism – polflucht (flight from the poles) – which assumed that supercontinents had formed in polar regions to be subject to centrifugal force resulting from Earth’s rotation. This broke them apart to be driven towards the Equator. Such a mechanism being easily invalidated, most contemporary geologists preferred to ‘throw Wegener’s  baby out with the bathwater’. Yet every piece of his evidence that continents had moved around and most of his ideas about the nature of their movements were steadily verified and amplified over the next six decades, which attracted more curious and flexible scientists. What is now the central paradigm of the Earth Sciences had to wait for a set of major discoveries in the 1950s and ‘60s enabled by emerging technologies, such as the magnetometers used by Fred Vine and Drummond Matthews to discover sea-floor magnetic striping and thus sea-floor spreading. Their breakthrough presented a plausible mechanism for continental drift and launched a near frenzy of collaborative research among a global milieu of young geoscientists, one of whom being W. Jason Morgan.

W. Jason Morgan outside the Department of Earth Sciences, Princeton University. (Credit: Denise Applewhite, Princeton University)

His initial interest was in the great fracture zones on the floors of the Atlantic and Pacific Oceans. He grasped that each of them was very nearly a great circle. This was a central key to unifying seafloor spreading and continental drift – to move across a spherical surface every point on the seafloor had to follow such a path. Morgan recognised that the fracture zones could only result from rigid plates having to fracture to accommodate that motion. Using spherical geometry he was able to link together ridges, trenches and these huge transform faults with poles of rotation and triple junctions to predict plate motions in a quantitative manner. That insight provided a key to active earthquakes, mountain belts and volcanoes. His scientific unification was a result of genius: in just a few weeks Morgan established the fundamentals of what became known as plate tectonics.

W. Jason Morgan was one of the revolutionaries who made geology dynamic and launched its resurrection from the boring province of damp field workers in anoraks tramping across tracts of extremely puzzling rocks and structures, noses to the ground. He died at the age of 87 on 31 July 2023.

You can read an obituary by his former research student Richard Hey and his son Jason Phipps Morgan together with a fuller account of his career on Wikipedia.

Music based on earthquake waves

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Many readers will have heard the vibration signal of an earthquake, as recorded by a seismometer, and replayed through a speaker: listen to some examples here. They are eerily like the sounds of falling, multi-storey buildings. Scary, especially if you think of the horrors of the devastation in SE Turkiye and NE Syria caused by the 6 February 2023 magnitude 7.8 event on the East Anatolian Fault system

Since P-waves are very like sound waves, audibly converting the one to the other is relatively simple. However, earthquakes are rarely single events, each major one being preceded by foreshocks and followed by aftershocks, both recurring over weeks or months. Highly active areas are characterised by earthquake swarms that can go on continuously, as happens with sea-floor spreading at mid-ocean ridges. In the case of Yellowstone National Park there are continual quakes, but there the seismicity results from magma rising and falling above a superplume. Most of such swarm-quakes are diminutive, so playing the speeded-up signal through a loudspeaker just sounds like a low, tremulous hiss.

Domenico Vicinanza a physicist at the Anglia Ruskin University in Cambridge UK specialises in creating music from complex scientific data, including those from CERN’s Large Hadron Collider in Geneva, to help interpret them. He has recently turned his hand to the Yellowstone earthquake swarm, converting the amplitudes and frequencies of its real-time seismograph to notes in a musical score: listen to the results here. They are surprisingly soothing, perhaps in the manner of the song of the humpback whale used by some to help with their chronic insomnia.

See also:  Davis, N. Rock concert: Yellowstone seismic activity to be performed on live flute, The Guardian; 8 May 2023

Amber, palaeontologists and a military dictatorship

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Most people are familiar with the term ‘blood diamonds’, meaning diamonds clandestinely exported from areas infested by the lethal activities of military and paramilitary forces. Indeed such conflicts are often fuelled by the large profits to be made from trading diamonds.  One such source was in Sierra Leone during the civil war of 1991-2002. Others include Liberia, Côte d’ Ivoire, Angola and the Democratic Republic of Congo. Like illicit money, gemstones can be ‘laundered’ and find their way into conventional trade. To some extent the blood diamond trade has been slowed down by a programme of certification of packaged uncut diamond ‘rough’ by bona fide producers, and banning the sale of uncertified rough. The Kimberley Programme has been criticised because certificates can be issued in corrupt ways, so that blood diamonds probably still make their way to the international diamond markets: certification may hold no fears for those who force people to ine at gun point. However, because diamonds often show geochemical signatures and minute inclusions of other minerals that are unique to individual pipe-like intrusions of kimberlite that carry deep-mantle material to the surface. So, it is technically possible – but costly – to check for suspect rough. Such controls do not apply to other gemstones. A major source of very-high value gems is Myanmar (formerly Burma), whose widely condemned military dictatorship may be engaged in their unethical trade, including smuggling to neighbouring Thailand and China to avoid scrutiny.

Foot of bird chick preserved in Cretaceous amber from Kachin, Myanmar. Credit: Pinterest, Xing Lida, China University of Geosciences)

Myanmar is well endowed with sedimentary deposits that contain amber, the solidified resin from a variety of now extinct trees. Oddly, completely clear amber has low intrinsic value: it is semi-precious, albeit attractive. But it often contains inclusions of vegetation fragments, insects, feathers and small vertebrates, of interest to palaeontologists. Myanmar amber is especially interesting as it is dated to the Middle Cretaceous (~130 Ma), older than that found around the Baltic Sea (Eocene ~44 Ma), which was the main source for European jewellery since the 12th century, and that from Canada (Upper Cretaceous ~80 Ma). Myanmar amber has been used decoratively and medicinally in China since the 3rd century CE, and in Europe since prehistoric times. It is attractive but quite common, so historically amber never commanded high prices but was widely used as a trade item. Since the publicity attending the supposed extraction of dinosaur DNA from the bodies of reptile parasites to resurrect dinosaurs in Steven Spielberg’s 1993 film Jurassic Park, public and scientific interest in amber has boomed. It is primarily the exquisite preservation of encased organisms that piques the interest of palaeontologists. Papers that rely on the Myanmar amber have grown in number over the last ten years, despite the country being infamous for military repression of tribal and religious groups in its rural areas.

One of the most conflict-riven areas is the northern state of Kachin where the most interesting amber to palaeontologists is collected by the Kachin people of the Hukawng Valley. Government forces have been in conflict with the Kachin Independence Army since the 1960s, most particularly for control of the amber industry. A recent paper has focussed on the ethical issue of publications based on fossil-bearing amber from the area (Dunne, E.M. et al. 2022. Ethics, law, and politics in palaeontological research: The case of Myanmar amber. Communications Biology, v. 5, article no. 1023; DOI: 10.1038/s42003-022-03847-2).

In 2010 the military began forcibly to take over mines in Kachin.  Between 2014 and 2021 the annual number of publication underwent a tenfold growth from between 10 to 15 to over 150, despite the fact that in 2015 the government in Yangon prohibited removal of fossils from the country. But the export laws exempt gemstones, so the growing demand for fossiliferous amber is clearly reflected in its supply to foreign scientists.  Rare specimens that include vertebrate remains command prices up to US$100,000. The Myanmar amber trade is now estimated at around US$ 1 billion per annum. The Myanmar military took over all the mines in 2017, and is clearly the main supplier to palaeontologists.

In the seven-year period, only 3 papers out of 872 included contributors from Myanmar, which also suggests an element of ‘parachute science’: unsurprisingly Myanmar-based scientists also find it difficult to visit the Kachin area. Before 2014 most of the 69 publications involved scientists in the US; since then, the top spot has been occupied by Chinese scientists who have amassed 417. It seems clear that there is a web of contacts linking together the source of Myanmar amber, its market and science. In 2020 the Society of Vertebrate Paleontology called for a moratorium on publishing data from Kachin sources. But since then there is little sign that palaeontologists have taken any notice.

See also: Ortega, R.P. 2022. Violent conflict in Myanmar linked to boom in fossil amber research, study claims. Science v. 378, p.10-11; DOI: 10.1126/science.adf0973 (This commentary includes opinion that seeks to mitigate the views of Emma Dunne and colleagues)

British government fracking fan fracked

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In November 2019 the Conservative government of Boris Johnson declared a moratorium on development of shale gas by hydraulic fracturing (‘fracking’) in England. This followed determined public protests at a number of potential fracking sites, the most intransigent being residents of Lancashire’s Fylde peninsula. They had been repeatedly disturbed since mid 2017 by low-magnitude earthquakes following drilling and hydraulic-fluid injection tests by Cuadrilla Resources near Little Plumpton village. Their views were confirmed in a scientific study by the British Geological Survey for the Oil and Gas Authority that warned of the impossibility of predicting the magnitude of future earthquakes that future fracking might trigger. The shale-gas industry of North America, largely in areas of low population and simple geology, confirmed the substantial seismic hazard of this technology by regular occurrences of earthquakes up to destructive magnitudes greater than 5.0. The Little Plumpton site was abandoned and sealed in February 2022.

Cuadrilla’s exploratory fracking site near Little Plumpton in Fylde, Lancashire. (Credit: BBC)

On 22 September 2022 the moratorium was rescinded by Jacob Rees-Mogg, Secretary of State for Business, Energy and Industrial Strategy in the new government of Liz Truss, two weeks after his appointment. This was despite the 2019 Conservative manifesto pledging not to lift the moratorium unless fracking was scientifically proven to be safe. His decision involved suggesting that the seismicity threshold for pausing fracking operations be lifted from magnitude 0.5 to 2.5, which Rees-Mogg claimed without any scientific justification to be ‘a perfectly routine natural phenomenon’.  He further asserted that opposition to fracking was based around ‘hysteria’ and public ignorance of seismological science, and that some protestors had been funded by Vladimir Putin. In reality the Secretary of State’s decision was fuelled by the Russian Federation’s reducing gas supplies to Europe following its invasion of Ukraine, the soaring world price of natural gas and an attendant financial crisis. There was also a political need to be seen to be ‘doing something’, for which he has a meagre track record in the House of Commons. Rees Mogg claimed that lifting the moratorium would bolster British energy security. That view ignored the probable lead time of around 10 years before shale gas can become an established physical resource in England. Furthermore, an August 2018 assessment of the potential of UK shale-gas, by a team of geoscientists, including one from the British Geological Survey, suggested that shale-gas potential would amount to less than 10 years supply of UK needs: contrary to Rees-Mogg’s claim that England has ‘huge reserves of shale’. Indeed it does, but the vast bulk of these shales have no commercial gas potential.

Ironically, the former founder of Cuadrilla Resources, exploration geologist Chris Cornelius, and its former public affairs director, Mark Linder, questioned the move to unleash fracking in England, despite supporting shale-gas operations where geologically and economically appropriate. Their view is largely based on Britain’s highly complex geology that poses major technical and economic challenges to hydraulic fracturing. Globally, fracking has mainly been in vast areas of simple, ‘layer-cake’ geology. A glance at large-scale geological maps of British areas claimed to host shale-gas reserves reveals the dominance of hundreds of faults, large and small, formed since the hydrocarbon-rich shales were laid down. Despite being ancient, such faults are capable of being reactivated, especially when lubricated by introduction of fluids. Exactly where they go beneath the surface is unpredictable on the scales needed for precision drilling.  Many of the problems encountered by Cuadrilla’s Fylde programme stemmed from such complexity. Over their 7 years of operation, hundreds of millions of pounds were expended without any commercial gas production. Each prospective site in Britain is similarly compartmentalised by faulting so that much the same problems would be encountered during attempts to develop them. By contrast the shales fracked profitably in the USA occur as horizontal sheets deep beneath entire states: entirely predictable for the drillers. In Britain, tens of thousands of wells would need to be drilled on a ‘compartment-by-compartment’ basis at a rate of hundreds each year to yield useful gas supplies. Fracking in England would therefore present unacceptable economic risks to potential investors. Cornelius and Linder have moved on to more achievable ventures in renewables such as geothermal heating in areas of simple British geology.

Jacob Rees-Mogg’s second-class degree in history from Oxford and his long connection with hedge-fund management seem not to be appropriate qualifications for making complex geoscientific decisions. Such a view is apparently held by several fellow Conservative MPs, one of whom suggested that Rees-Mogg should lead by example and make his North East Somerset constituency the ‘first to be fracked’, because it is underlain by potentially gas-yielding shales. The adjoining constituency, Wells, has several sites with shale-gas licences but none have been sought within North East Somerset. Interestingly, successive Conservative governments since 2015, mindful of a ‘not-in-my-backyard’ attitude in the party’s many rural constituencies, have placed a de-facto ban on development of onshore wind power.