Category: Palaeobiology

New ideas on the origins of Eukaryotes

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In 1967 the American biologist Lyn Margulis developed an idea that had been considered earlier in the 20th century. It proposed that the complex architecture of eukaryote cells had arisen by several simpler prokaryote cells becoming incorporated inside a membrane to form other bodies or organelles that co-existed and interacted. That is, a complex of mutual dependence within a cell wall, called endosymbiosis. For instance, the mitochondria of modern animal cells resemble a class of aerobic bacteria or Proteobacteria (gram-negative bacteria), some of which are responsible for several modern diseases, such as tick-bite fevers. Another is the resemblance of the photosynthesising chloroplasts of plants to cyanobacteria. A similar origin might apply to eukaryote nuclei and other organelles inside eukaryote cells; some have their own DNA molecules. I summarised Margulis’s late-20th century concept of endosymbiosis in my 1999 book Stepping Stones.

AI generated cartoon of symbiogenesis. Credit PhysOrg

Since then the rapid development of genome analysis has seen major advances in the field now known as symbiogenesis. In the most general sense, that is now regarded as a sequence of mergers between early members of the two prokaryote domains of Archaea and Bacteria: not a simple topic! In 2017 a group of archaeons called Promethearchaeati – ‘Asgard’ for short – were found to contain proteins – and thus the genes that produce them – akin to those in eukaryotes. So the Asgards are prime candidates for a role in symbiogenesis. Their symbiotic merger with a Proteobacteria may have begun the evolution of all eukaryotes. The entry of cyanobacteria – a candidate for chloroplasts – into one of the evolving groups divided plants from animals. A new AI analysis of thousands of genomes in living microbial organisms by Catalan scientists in Barcelona has enabled them to flesh-out and critique this hypothesis to a remarkable extent (Bernabeu, M. et al. 2026. Gene ancestries reveal diverse microbial associations during eukaryogenesis. Nature, v. 654; DOI: 10.1038/s41586-026-10639-9). Their work possibly revolutionises the study of biological evolution

Moisès Bernabeu and his three colleagues drastically ‘pruned’ the eukaryotic tree of life, which over-represents animals and species found in common ecosystems. They also stripped the limited number of eukaryote genomes of genes that do simple jobs or are closely related – i.e. those that seem to duplicate large sections from the oldest, ancestral genes. Two further ‘edits’ enabled the team to judge from their analysis what sort of roles may have been played by the genetics of the last eukaryote common ancestor (LECA). At this level of simplification it appeared that our ancestors inhabited oxygenated environments and got their energy by eating other organisms or their dead remains.

About 30% of the genes in eukaryotes seem to be unique to them and evolved after LECA had emerged. Many of the rest came from diverse prokaryote organisms. Alphaproteobacteria (previously termed ‘purple’ bacteria) and the Asgard archaea figure strongly, together with a range of other bacteria. As suggested previously, a vital process could have been transfer of genes from one prokaryote to another. Bernabeu et al.’s study highlights waves of such gene transfers prior to LECA’s acquisition of mitochondria, widely deemed to have been incorporation of an early proteobacterium. They also provide evidence for a central role played by giant viruses in enabling such gene transfers, also hypothesised previously.

Rather than being a simple case of a ‘one-off’ symbiosis between two separate prokaryotes, an archaeon and a bacterium, with the other organelles and genes added during a later evolutionary stage, the genesis of LECA was probably a long and complex interaction that involved diverse participants. It also seems certain that all the prokaryotes must have interacted in a stable, long-lived ecosystem for such a complex process to reach a tangible and enduring outcome after innumerable fits and starts. That oxygen became such an essential inorganic ‘player’ clearly suggests a microbial-mat ecosystem of organisms that involved oxygenic photosynthesis. The whole ecosystem and its members, pro- and eukaryotic, seem likely to have been evolving together, like modern ecosystems but on a microscopic scale. All this may have taken millions of years during the Palaeoproterozoic Era (2.5 to 1.6 Ga)

See also: Timmer, J. 2026. The first complex cells had genes from a complex mix of species. Arstechnica.com, 11 June 2026;  Microbial alliances, not mitochondria alone, may have built first eukaryotic cells. Phys.org, 10 June 2026.

Frozen squirrel excrement excites Pleistocene ecologists

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An arctic ground squirrel (Urocitellus parryii)

Lately, North American ground squirrels have been observed hunting, dismembering and eating voles. European tree squirrels also have a side that negates their nut-nibbling popular personae. They regularly take fledglings from bird nests. No more Mr Cute Squirrel then! In fact they’ll eat just about anything, including roadkill and even washed-up dead whales. A team of forensic ecologists from Canada, Sweden, Denmark and the US has harnessed this trait into a possibly ground-breaking study of how the Yukon Territory ecosystem evolved during the Pleistocene since 700 ka ago (Murchie, T.J. and 15 others 2026. Ground squirrel coprolites preserve complex archives of ancient environmental DNA over 700,000 years. Nature Communications, v. 17, article 4868; DOI: 10.1038/s41467-026-72977-6). Between 2007 and 2021 Tyler Murchie and colleagues collected ground squirrels’ faecal pellets from 14 latrine chambers or middens in their ancient burrows in a sequence of permafrost layers at the famous Klondike goldfields. The uppermost layers were dated using the 14C method, and for samples from deeper levels – older than 50 ka – using volcanic ash layers in the frozen sediments. Fourteen of the samples spanning 17 to 700 ka ago yielded fragmentary DNA from the squirrels’ diet.

Ground-squirrel midden in tunnelled permafrost. Credit Scott Cocker, University of Alberta)

Obviously this was dominated by their own DNA and gut bacteria, but contained fragments from an astonishing range of organisms that they had eaten. There were signs of at least 200 plant species: trees, shrubs grasses and flowering herbs known from the Pleistocene ‘mammoth steppe’ and tundra. Animal DNA included that from spiders, ants, moths, beetles, and grasshoppers, together with parasitic worms. But the most astonishing range of their appetites covers a great many mammals. As well as small mammals, such as mice, there are also signs of bison, mammoths, horses, sheep, wolves, and big cats having been eaten. It hardly needs to be emphasised that the Pleistocene ground squirrels did not hunt and overwhelm such prey, but they certainly did not reject a free meal of carrion lying on the tundra.

The wealth of species unwittingly archived by ground squirrels’ tendency to hide their droppings within their burrow systems offers a novel means of tracking the evolution of the ecosystem of which they were a part. It seems to outweigh the use of DNA extraction from soil horizons or even fossil bones. But to take matters further would require many more samples spread more evenly through the history of the mammoth steppe and tundra – most of the samples are from the last 90 ka. The Klondike goldfields are not representative of the whole of Arctic North America, being in a rugged terrain. Moreover, the Yukon Territory was repeatedly glaciated, as was the Canadian Shield itself. So, intact permafrost sequences spanning even the last glacial period are rare.

See also: A snapshot in time: Ancient ground squirrel droppings, dating back 700,000 years, reveal rich details about evolutionary history of the Arctic. EurekAlert 9 June 2026.

Were giant octopuses top predators during the Cretaceous?

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Octopuses defy common sense. They are invertebrate molluscs, so we don’t expect them to show well-developed intelligence, which they do. As well as tiptoeing around on their eight tentacles, they can move at high speed using a kind of backwards jet propulsion and some are even able to cross dry land.. Each of their tentacles has a sort of brain, as well their central one: distributed, semi-autonomous cognition in which their tentacles taste, touch, and move independently. Three hearts circulate their blue blood. Masters of swift camouflage using specialised skin cells that contain different coloured pigments, which behave like pixels in a TV screen. Octopuses can also rapidly manipulate their body texture and shape. They also seem to use such bizarre displays to communicate mood, at the very least.

Shape-shifting octopuses can squeeze through gaps far smaller than their own size to hide from both predators and their prey, which also makes them escapologists far outranking Harry Houdini. Their eyes look like those of goats, with horizontally linear pupils, although they evolved separately from the eyes of other animals.  Satan is said to have goat-eyes, hence the colloquial name for an octopus: devil fish. Mariners of old (and maybe some of the present day) reputedly feared giant octopuses to be capable of crushing ships and devouring the crew: the Kraken! Even small octopuses possess greater intelligence than a dog: some seem to enjoy playing, building dens, negotiating mazes and watching the antics of humans …

Since they are almost entirely soft flesh, the fossil record of octopuses is unsurprisingly meagre, apart from their jaws that use chitinous ‘beaks’ to munch their victims. The evolution of other cephalopods, for instance ammonites and squids, is better known from their external and internal skeletal remains and extends back to the Cambrian Period. So collecting and analysing fossil octopus jaws is the only option for palaeontologists. Shin Ikegami of Hokkaido University, together with Jörg Mutterlose of Ruhr University in Bochum Germany and eight other Japanese scientists, developed a new approach to supplement data on octopus jaws previously excavated from Cretaceous strata on Hokkaido and Vancouver Islands. (Ikegami, S. and 9 others 2026. Earliest octopuses were giant top predators in Cretaceous oceans. Science,  v. 392, p. 406-410; DOI: 10.1126/science.aea6285).

Cretaceous marine predators (at maximum estimated size) with a scuba diver for scale. Credit: After Ikegami et al. Fig. 4, and Jacobs 2026.

Ikegami et al. ground layer by layer through Japanese and Canadian sedimentary rocks to produce 3-D tomographic models of fossil beaks within them – quicker CT scanning proved inefficient in showing details. All the ‘beaks’ showed signs of wear from cracking the harder bones of their prey. Assuming that the same variation of beak size and body mass as in modern octopuses is relevant to those of Cretaceous age, the researchers came up with an astonishing result. Cretaceous octopuses reached huge sizes. They estimated one Nanaimoteuthis jeletzkyi to have been 19 metres long, roughly the size of an articulated truck. During the Cretaceous Period the top predator of the oceans had long been supposed to have been the formidable marine reptile Mosasaurus at around 15 m long.

We know what mosasaurs ate from fossilised stomach contents of two specimens: more or less anything, including other substantial marine reptiles, sharks, cephalopods and even other mosasaurs, some whole, some dismembered. As for Nanaimoteuthis and other giant Cretaceous octopuses, reconstructed from their fossilised beaks, there is little obvious evidence for what they ate, other than it would have had to have been in large amounts. Judging from the wear exhibited by their beaks at least a proportion of their diet was crunched up shells and bones of ammonites and fish. Modern octopus species, both small and moderately large, have other sorts of feeding strategies. Some eat planktonic animals, others drill holes in shells and suck out their innards rendered to the texture of a ‘smoothie’ by corrosive saliva.

It is not surprising that the media have made quite a fuss of these Cretaceous ‘krakens’, some suggesting that they preyed on formidable marine reptiles such as mosasaurs. That would definitely have made them ‘top’ marine predators. Yet such massive, moving mounds of nourishing flesh would have made them a worthwhile catch for a whole school of toothy reptiles and sharks. The modern sperm whale is known to devour giant squid at the great depths to which they can dive, as witnessed by numerous cephalopod beaks in their stomachs. So it is equally possible that the octopus beaks found in Cretaceous sediments of Hokkaido were excreted by marine reptiles

See also: Jacobs, P. 2026. Truck-size octopuses stalked Cretaceous seas. Science, v. 392, 23 April 2026; DOI: 10.1126/science.z8o79rn; Devlin, H. 2026. ‘Kraken-like’ giant octopuses 100m years ago crunched bones of prey. The Guardian, 23 April 2026.

Asteroid Bennu: a ‘lucky dip’ for NASA and planetary science

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I must have been about ten years old when I last saw a ‘lucky dip’ or ‘bran tub’ at a Christmas fair.  You paid two shillings (now £0.1) to rootle around in the bran for 30 seconds and grab the first sizeable wrapped object that came to hand:. In my case that would be a cheap toy or trinket, but you never knew your luck as regards the top prize. There is a small asteroid called 101955 Bennu, about half a kilometre across, whose orbit around the Sun crosses that of the Earth. So it’s a bit scary, being predicted to pass within 750,000 km of Earth in September 2060 and has a 1 in 1,880 chance of colliding with us between 2178 and 2290 CE. Because Earth-crossing asteroids are a cheaper target than those in the Asteroid Belt, in 2016 NASA launched a mission named OSIRIS-REx to intercept Bennu, image it in great detail, snaffle a sample and ultimately return the sample to Earth for analysis. This wasn’t a shot in the dark, as a lot of effort and funds were expended to target and then visit Bennu. But unlike me at the fair ground, NASA will be very happy with the outcome.

The asteroid Bennu, showing its oblate spheroidal shape, due to rotation, and its rubbly structure. Source: NASA/Goddard/University of Arizona via Wikimedia Commons

Bennu is a product of what might be regarded as ‘space sedimentation’, indeed a kind of conglomerate, being made up of boulders up to 58 m across set in gravelly and finer debris or ‘regolith’. High-resolution images revealed veins of carbonate minerals in the boulders. They suggest hydrothermal activity in a much larger parent body – one of many proto-planets accreted from interstellar gas and dust as the Solar System first began to form over 4.5 billion years ago. Its collision with another sizeable body knocked off debris to send a particulate cloud towards the Sun, subsequently to clump together as Bennu by mutual gravitational attraction. The carbonate veins can only have formed by circulation of water inside Benno’s  parent.

The ‘REx’ in the mission’s name is an acronym for ‘Regolith Explorer’. Sampling was accomplished on 20 October 2020 by a soft landing that drove a sample into a capsule, and then OSIRIS-REx ‘pogo-sticked’ off with the booty. The capsule was dropped off by parachute after the mission’s return on 24 September 2023, in the manner of an Amazon delivery by drone to a happy customer. So, you can understand my ‘lucky dip’ metaphor. And NASA certainly was ‘lucky’ as the contents turned out to be astonishing, as related two years later by the analytical team in the US, led by NASA’s Angel Mojarro (Mojarro, A. et al. 2025.Prebiotic organic compounds in samples of asteroid Bennu indicate heterogeneous aqueous alteration. Proceedings of the National Academy of Science, v. 122, article e2512461122; DOI: 10.1073/pnas.2512461122).

The rock itself is made from bits of carbonaceous chondrite, the most primitive matter orbiting the Sun. It contains fifteen amino acids, including all five nucleobases that make up RNA and DNA – adenine (A), guanine (G), cytosine (C), thymine (T) and uracil (U) – as in AUGC and AGCT. Benno’s complement of amino acids included 14 of the 20 used by life on Earth to synthesise proteins. The fifteenth, tryptophan, has never confidently been seen in extraterrestrial material before. Alkylated polycyclic aromatic hydrocarbons, also found in Bennu, are seen in abundance in interstellar gas clouds and comets by detecting their characteristic fluorescence when illuminated by mid-infrared radiation from hot stars using data from the Spitzer and James Webb Space Telescopes. These prebiotic organic compounds have been suggested to have played a role in the origin of life, but exposure to many produced by human activities are implicated in many cancers and cardiovascular issues.  A second paper by Japanese biochemists and colleagues from the US was also published in early December 2025 (Furukawa, Y. and 13 others 2025. Bio-essential sugars in samples from asteroid Bennu. Nature Geoscience, v. 12, online article; DOI: 10.1038/s41561-025-01838). The authors identified several kinds of sugars in a sample from Bennu, including ribose – essential for building RNA – and glucose. Bennu also contains formaldehyde – a precursor of sugars – perhaps originally in the same brines in which the amino acids formed.

Yet another publication coinciding with the aforementioned two focuses on products of the oldest event in the formation of Bennu: its content of pre-solar grains (Nguyen, A.N. et al. 2025. Abundant supernova dust and heterogeneous aqueous alteration revealed by stardust in two lithologies of asteroid Bennu. Nature Astronomy, v. 9, p. 1812-1820; DOI: 10.1038/s41550-025-02688-3).  In 1969 a 2 tonne carbonaceous chondrite fell near Allende in Mexico. The largest of this class ever found, it contained tiny, pale inclusions that eight years of research revealed to represent materials completely alien to the Solar System. They are characterised by proportions of isotopes of many elements that are very different from those in terrestrial materials. The anomalies could only have formed by decay of extremely short-lived isotopes that highly energetic cosmic rays produce in a manner analogous to neutron bombardment: they are products of nuclear transmutation. It is possible to estimate when the parent isotopes produced the anomalous ‘daughter’ products. One study found ages ranging from 4.6 to 7.5 Ga: up to three billion years before the Solar System began to form. It is likely that the grains are literally ‘star dust’ formed during supernovae in nearby parts of the Milky Way galaxy. Bennu samples contain six-times more presolar grains than any other chondritic meteorites. Nguyen et al. geochemically teased out grains with different nucleosynthetic origins. These ancient relics point to Bennu’s formation in a region of the presolar cloud that preceded the protoplanetary disk and was a mix of products from several stellar settings.

The results from asteroid Bennu support the key idea that that amino acid building blocks for all proteins and the nucleobases of the genetic code, together with other biologically vital compounds arose together in a primitive asteroid.  Its evolution provided the physical conditions, especially the trapping of water, for the interaction of simpler components manufactured in interstellar clouds. Such ‘fertile’ planetesimals and debris from them almost certainly accreted to form planets and endowed them with the potential for life. What astonishes me is that Bennu contains the five nucleobases used in terrestrial genetics and 70% of the amino acids from which all known proteins are assembled by terrestrial life. But, as I try to explain in my book Stepping Stones: The Making of Our Home World, life as we know it arose, survived and evolved through a hugely complex concatenation of physical and chemical events lasting more than 4.5 billion years. The major events and the sequences in which they manifested themselves may indeed have been unique. Earth is a product of luck and so are we!

See also: Tabor, A. et al. 2025. Sugars, ‘Gum,’ Stardust Found in NASA’s Asteroid Bennu Samples. NASA article 2 December 2025. Glavin, D.P. and 61 others 2025. Abundant ammonia and nitrogen-rich soluble organic matter in samples from asteroid (101955) Bennu. Nature Astronomy, v. 9, p. 199-210; DOI: 10.1038/s41550-024-02472-9

The ‘boring billion’ years of the Mesoproterozoic: plate tectonics and the eukaryotes

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The emergence of the eukaryotes – of which we are a late-entry member – has been debated for quite a while. In 2023 Earth-logs reportedthat a study of ‘biomarker’ organic chemicals in Proterozoic sediments suggests that eukaryotes cannot be traced back further than about 900 Ma ago using such an approach. At about the same time another biomarker study showed signs of a eukaryote presence at around 1050 Ma. Both outcomes seriously contradicted a ‘molecular-clock’ approach based on the DNA of modern members of the Eukarya and estimates of the rate of genetic mutation. That method sought to deduce the time in the past when the last eukaryotic common ancestor (LECA) appeared. It pointed to about 2 Ga ago, i.e. a few hundred million years after the Great Oxygenation Event got underway. Since eukaryote metabolism depends on oxygen, the molecular-clock result seems reasonable. The biomarker evidence does not. But were the Palaeo- and Mesoproterozoic Eras truly ‘boring’? A recent paper by Dietmar Müller and colleagues from the Universities of Sydney and Adelaide, Australia definitely shows that geologically they were far from that (Müller, R.D. et al. 2025. Mid-Proterozoic expansion of passive margins and reduction in volcanic outgassing supported marine oxygenation and eukaryogenesis. Earth and Planetary Science Letters, v. 672; DOI: 10.1016/j.epsl.2025.119683).

Carbon influx (million tons per year) into tectonic plates and into the ocean-atmosphere system from 1800 Ma to present. The colour bands represent: total carbon influx into the atmosphere (mauve); sequestered in tectonic plates (green); net atmospheric influx i.e. total minus carbon sequestered into plates (orange). The widths of the bands show the uncertainties of the calculated masses shown as darker coloured lines.

From 1800 to 800 Ma two supercontinents– Nuna-Columbia and Rodinia – aggregated nearly all existing continental masses, and then broke apart. Continents had collided and then split asunder to drift. So plate tectonics was very active and encompassed the entire planet, as Müller et al’s palaeogeographic animation reveals dramatically. Tectonics behaved in much the same fashion through the succeeding Neoproterozoic and Phanerozoic to build-up then fragment the more familiar supercontinent of Pangaea. Such dynamic events emit magma to form new oceanic lithosphere at oceanic rift systems and arc volcanoes above subduction zones, interspersed with plume-related large igneous provinces and they wax and wane. Inevitably, such partial melting delivered carbon dioxide to the atmosphere. Reaction on land and in the rubbly flanks of spreading ridges between new lithosphere and dissolved CO2 drew down and sequestered some of that gas in the form of solid carbonate minerals. Continental collisions raised the land surface and the pace of weathering, which also acted as a carbon sink. But they also involved metamorphism that released carbon dioxide from limestones involved in the crustal transformation. This protracted and changing tectonic evolution is completely bound up through the rock cycle with geochemical change in the carbon cycle.

From the latest knowledge of the tectonic and other factors behind the accretion and break-up of Nuna and Rodinia, Müller et al. were able to model the changes in the carbon cycle during the ‘boring billion’ and their effects on climate and the chemistry of the oceans. For instance, about 1.46 Ga ago, the total length of continental margins doubled while Nuna broke apart. That would have hugely increased the area of shallow shelf seas where living processes would have been concentrated, including the photosynthetic emission of oxygen. In an evolutionary sense this increased, diversified and separated the ecological niches in which evolution could prosper. It also increased the sequestration of greenhouse gas through reactions on the flanks of a multiplicity of oceanic rift systems, thereby cooling the planet. Translating this into a geochemical model of the changing carbon cycle (see figure) suggests that the rate of carbon addition to the atmosphere (outgassing) halved during the Mesoproterozoic. The carbon cycle and probable global cooling bound up with Nuna’s breakup ended with the start of Rodinia’s aggregation about 1000 Ma ago and the time that biomarkers first indicate the presence of eukaryotes.

Simplified structures of (a) a prokaryote cell; (b) a simple eukaryote animal cell. Plants also contain organelles called chloroplasts

So, did tectonics play a major role in the rise of the Eukarya? Well, of course it did, as much as it was subsequently the changing background to the appearance of the Ediacaran animals and the evolutionary carnival of the Phanerozoic. But did it affect the billion-year delay of ‘eukaryogenesis’ during prolonged availability of the oxygen that such a biological revolution demanded? Possibly not. Lyn Margulis’s hypothesis of the origin of the basic eukaryote cell by a process of ‘endosymbiosis’ is still the best candidate 50 years on. She suggested that such cells were built from various forms of bacteria and archaea successively being engulfed within a cell wall to function together through symbiosis. Compared with prokaryote cells those of the eukaryotes are enormously complex. At each stage the symbionts had to be or become compatible to survive. It is highly unlikely that all components entered the relationship together. Each possible kind of cell assembly was also subject to evolutionary pressures. This clearly was a slow evolutionary process, probably only surviving from stage to stage because of the global presence of a little oxygen. But the eukaryote cell may also have been forced to restart again and again until a stable form emerged.

See also: New Clues Show Earth’s “Boring Billion” Sparked the Rise of Life. SciTechDaily, 3  November 2025

AI unravels chemical signs of the earliest life on Earth

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Evidence for the earliest life on Earth has largely relied on finding signs of structures that may have been created during the Archaean Eon by micro-organisms. Actual fossils don’t turn up until the Proterozoic. The most distinctive and diverse of these are members of the Ediacaran fauna dated at around 635 Ma . The oldest widely accepted multi-celled eukaryote fossil was found in 2.1 billion-year old sediments from Gabon (see: The earliest multicelled life; July 2010). There have been a few claims for biogenic material, such as microscopic tubular structures in 3.5 billion-year (Ga) old pillow lavas and 3.2 Ga cherts from South Africa (see: Early biomarkers in South African pillow lavas; April 2004 and Believable Archaean fossils; March 2010) which some researchers dispute. Then there are Archaean stromatolites, which may be evidence for bacterial mats. The oldest of them have been claimed to occur in the famous, 3.77 Ga Isua metasediments of West Greenland. But such early fossils are chance finds, so geochemists have entered the arena with attempts to find irrefutable chemical signatures for life in ancient rocks.

One approach is isotope geochemistry. Carbon isotope data have been widely used, because life processes, such as photosynthesis, result in a deficiency of 13C relative to 12C. This was tried on graphite crystals trapped in sedimentary phosphate minerals from Isua. The results were at first acclaimed as a sign of life at around 3.8 Ga, but then refuted. In 2015 a similar approach was applied to graphite trapped in a 4.1 Ga detrital zircon, seemingly pushing back evidence for life into the Hadean. But zircon is a mineral produced by crystallisation of magma, so the fractionation of carbon isotopes in trapped graphite seem unlikely to shed light on the earliest life. The main drawback to using carbon isotopes is because metamorphism, Fischer-Tropsch mechanisms in hydrothermal environments, and volcanic processes may be responsible for enrichment of lighter carbon isotopes relative to 13C. The relative abundance of the different isotopes of iron in Archaean sediment may give clues to the transient availability of oxygen generated by bacterial photosynthesis that would oxidise soluble Fe2+ to insoluble Fe3+. Promising results were obtained in 2013 from 3.8 Ga banded ironstones at Isua. But doubt was again raised, so the only generally accepted evidence is that of the microfossils found in hydrothermal cherts in Palaeoarchaean pillow lavas from South Africa and Western Australia and the earliest stromatolites, all around 3.4 to 3.5 Ga old. However, recent research may have opened up a more convincing route to tracking down ancient life forms –actual organic molecules that make up or are produced by organisms.

Michael Wong and co-workers at the Carnegie Institution for Science in Washington, DC, USA together with other colleagues from the US, Austria, Canada, China, Belgium, Norway, Australia, the UK and France used artificial intelligence to wade through the results of geochemical analysis of over 400 ancient and modern carbon-bearing samples. (Wong, M.I. and 28 others 2025. Organic geochemical evidence for life in Archean rocks identified by pyrolysis–GC–MS and supervised machine learning. Proceedings of the National Academy of Sciences, v. 122, article e2514534122: DOI: 10.1073/pnas.2514534122). Their objective was to track the presence of organically derived molecules as far back as possible. Their approach bears a passing resemblance to that used to build genomes of ancient fossils from broken bits of DNA that reside in them. Like DNA, bio-molecules degrade over time, but leave fragments in rocks that can be detected using pyrolysis gas chromatography and mass spectrometry. In itself PGC-MS is not especially new, but using artificial intelligence (machine learning) on a massive date set certainly is: perhaps the first major trial of AI in geology.

Percentages of samples designated as biogenic by Wong et al’s AI analysis. Credit: Wong et al, Fig 4

Their samples were not just ancient rocks going back into the Archaean as far back as 3.5 Ga, but included modern biological material, meteorites presumed to have been devoid of life since their origin in pre-solar system times and synthetic samples. Wong et al divided 272 samples with known biological affinities into 9 groups to train the AI algorithm. The analytical method breaks down organic and inorganic carbonaceous materials into fragments of molecules: the opposite of DNA sequencing. When subjected to PGC-MS each type of living organism, from bacteria to animals produces a distinct pattern of molecular fragments. The AI analysis is based on a sophisticated statistical algorithm being trained to recognise ‘debris’ from organic and inorganic carbonaceous compounds according to each sample’s geochemical ‘fingerprint’. Part of the ‘training’ was based on sediments that contain irrefutable fossil samples from as far back in time as the Mesoproterozoic (1000 Ma). Another part was based on definitely inorganic materials, such as carbonaceous meteorites. AI proved able to distinguish biological from inorganic material with a probability up to 0.9 (90%). These results suggested that older, more biologically uncertain material could be assessed.

The AI was able to distinguish general biogenic affinities from inorganic ones in samples with decreasing success going back in time: as high as 0.93 in the Phanerozoic to 0.47 in the Archaean. The oldest samples that reached the probability threshold for this distinction (0.6) were 3.3 Ga cherts from the Barberton Greenstone Belt in South Africa. Another distinction between photosynthetic and and non-photosynthetic affinities among the samples that ‘passed’ as probably biotic reached the 0.6 probability threshold at 2.5 Ga for a sample from South Africa. Non-photosynthetic, but still probably biotic samples extend as far back as 3.5 Ga in South African and Western Australian Greenstone Belts.

Although Wong et al’s preliminary exploration with their novel approach doesn’t take us beyond the current 3.4 to 3.5 Ga age for the earliest tangible suggestions of life. However, they note ‘…our sample inventory is notably lacking in ancient abiogenic samples’. This is a good indication of the promise for further progress that the approach offers. Previous research has sought intact biogenic molecules, with not a great deal of luck, over several decades. Their final conclusion is ‘…information-rich attributes of ancient organic matter, even though highly degraded and with few if any surviving biomolecules, have much to reveal about the nature and evolution of life.’ They have opened a very important avenue in palaeobiological research , as their methodology seems capable of fine tuning to all manner of pro- and eukaryote biochemical distinctions. It could even be used with extraterrestrial material, should we ever get any …

See also: Walsh, E. 2025. Researchers report earliest molecular evidence of photosynthetic life. Chemical & Engineering News, 18 November 2025.

A ‘worm’ revolution and ecological transition before the Cambrian explosion

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Bioturbated ‘pipe rock’ of the basal Cambrian sandstones of NW Scotland. Credit: British Geological Survey photograph P531881

About 530 Ma ago most of the basic body plans of today’s living organisms can be detected as fossils, i.e. preserved hard parts. Yet studies of trace fossils (ichnofossils) – marks left in sediments by active soft bodied creatures suggest that many modern phyla arose before the start of the Cambrian (~539 Ma), as early as 545 Ma. So the term ‘Cambrian explosion’ seems to be a bit of a misnomer on two counts: it lasted around 15 Ma and began before the Cambrian. Preceding it was the Ediacaran Period that began around 100 Ma earlier in the Neoproterozoic Era. Traces of its eponymous fauna of large soft-bodied organisms are found on all continents, but apparently none of them made it into the Phanerozoic fossil record. Another characteristic of the Ediacaran is that its sedimentary rocks – and those of earlier times – show no signs of burrowing: they are not bioturbated. That may be why the Ediacaran pancake-, bun-, bag- and pen-like lifeforms are so remarkably well preserved. But a lack of burrowing did not extend to the beginning of Cambrian times. The most likely reason why it was absent during the early Ediacaran Period is that sea-floor sediments then were devoid of oxygen so eukaryote animals could not live in them. But the presence of these large organisms showed that seawater must have been oxygenated. Now clear signs of burrowing have emerged from study of Ediacaran rocks exposed in the Yangtze Gorge of Hubei,southern China ( Zhe Chen & Yarong Liu 2025. Advent of three-dimensional sediment exploration reveals Ediacaran-Cambrian ecosystem transition. Science Advances, v. 11, article eadx9449; DOI: 10.1126/sciadv.adx9449).

Tadpole-like trace fossils from the Ediacaran Dengying Formation in the Yangtze Gorge: 5 cm scale bars. The ‘heads’ show tiny depressions suggesting that there maker probed into the sediments as well as foraging horizontally. Credit: Zhe Chen & Yarong Liu; Figs 3B and 3D

Zhe Chen and Yarong Liu of the Nanjing Institute of Geology and Palaeontology and Chinese Academy of Sciences in China examined carbonates of the upper Ediacaran Dengying Formation. This overlies the Doushantuo Formation (550 to 635 Ma), known for tiny fossils of possibly the oldest deuterostome Saccorhytus coronaries; a potential candidate for the ancestor of modern bilaterian phyla. In the Yangtze Gorge locality sediments at this level show only traces of browsing of bacterial mats on the sediment surface; i.e. 2-D feeders. The basal Dengying sediments host clear signs that organisms could then penetrate into the sediments. These 3-D feeders , would have had access to buried organic remains, hitherto unexploited by living organisms. Such animal-sediment interactions would have disturbed and diminished the living microbial mats that held the sediment surface in place, and thus began to dismantle the substrate for the typical Edicaran fauna. Similar 3-D feeders occur throughout the 11 Ma represented by the Dengying Formation to the start of the Cambrian. This beginning of bioturbation heralded a period during which the Ediacaran fauna steadily waned. It also released nutrients into deep water, and opened up new ecological niches for more advanced animals on the seabed.  Dissolved oxygen could only slowly enter the sediments since atmospheric and oceanic O2 levels were low. But by the earliest Cambrian it had risen to about 5 to 10% by volume to support many other kinds of burrowing animals that could penetrate more deeply, as witnessed by the abundant sandstones that occur at the base of the Cambrian in Britain.

A possible Chinese ancestor for Denisovans, Neanderthals and modern humans

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

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

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

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

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

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

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

The end-Triassic mass extinction and ocean acidification

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

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

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

The mass extinction that ended the Triassic (~201 Ma) coincides with evidence for intense volcanism in South and North America, Africa and southern Europe, then at the core of the Pangaea supercontinent. Flood basalts and large igneous intrusions – the Central Atlantic Magmatic Province (CAMP) – began the final break-up of Pangaea. The end-Triassic extinction deleted 34% of marine genera. Marine sediments aged around 201 Ma reveal a massive shift in sulfur and carbon isotopes in the ocean that has been interpreted as a sign of acute anoxia in the world’s oceans, which may have resulted in massive burial of oxygen-starved marine animal life. However, there is no sign of Triassic, carbon-rich deep-water sediments that characterise ocean anoxia events in later times. But it is possible that bacteria that use the reduction of sulfate (SO42-) to sulfide (S2-) ions as an energy source for them to decay dead organisms, could have produced the sulfur isotope ‘excursion’. That would also have produced massive amounts of highly toxic hydrogen sulfide gas, which would have overwhelmed terrestrial animal life at continental margins. The solution ofH2S in water would also have acidified the world’s oceans.

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

Detecting oxygenic photosynthesis in the Archaean Earth System

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

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

A limestone made of stromatolites

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

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

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

Arsenic: an agent of evolutionary change?

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

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

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

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

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

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

Impact debris in Neoproterozoic sediments of Scotland and biological evolution?

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

The origin of life on Earth: new developments

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Debates around the origin of Earth’s life and what the first organism was like resemble the mythical search for the Holy Grail. Chivalric romanticists of the late 12th and early 13th centuries were pretty clear about the Grail – some kind of receptacle connected either with the Last Supper or Christ’s crucifixion – but never found it. Two big quests that engage modern science centre on how the chemical building blocks of the earliest cells arose and the last universal common ancestor (LUCA) of all living things. Like the Grail’s location, neither is likely to be fully resolved because they can only be sought in a very roundabout way: both verge on the imaginary. The fossil record is limited to organisms that left skeletal remains, traces of their former presence, and a few degraded organic molecules. The further back in geological time the more sedimentary rock has either been removed by erosion or fundamentally changed at high temperatures and pressures. Both great conundrums can only be addressed by trying to reconstruct processes and organisms that occurred or existed more than 4 billion years ago.

Artistic impression of the early Earth dominated by oceans (Credit: Sci-news.com)

In the 1950s Harold Urey of the University of Chicago and his student Stanley Miller mixed water, methane, ammonia and hydrogen sulfide in lab glassware, heated it up and passed electrical discharges through it. They believed the simple set-up crudely mimicked Hadean conditions at the Earth surface. They were successful in generating more complex organic chemicals than their starting materials, though the early atmosphere and oceans are now considered to have been chemically quite different. Such a ‘Frankenstein’ approach has been repeated since with more success (see Earth-logs April 2024), creating 10 of the 20 amino acids plus the peptide bonds that link them up to make all known proteins, and even amphiphiles, the likely founders of cell walls. The latest attempt has been made by Spanish scientists at the Andalusian Earth Sciences Institute, the Universities of Valladolid and Cadiz, and the International Physics Centre in San Sebastian (Jenewein, C. et al 2024. Concomitant formation of protocells and prebiotic compounds under a plausible early Earth atmosphere. Proceedings of the National Academy of Sciences, v. 122, article 413816122; DOI: 10.1073/pnas.241381612).

Biomorphs formed by polymerisation of HCN (Credit: Jenewein, C. et al 2024, Figure 2)

Jenewein and colleagues claim to have created cell-like structures, or ‘biomorphs’ at nanometre- and micrometre scale – spheres and polyp-like bodies – from a more plausible atmosphere of CO2 , H2O, and N2. These ‘protocells’ seem to have formed from minutely thin (150 to 3000 nanometres) polymer films built from hydrogen cyanide that grew  on the surface of the reaction chamber as electric discharges and UV light generated HCN and more complex ‘prebiotic’ chemicals. Apparently, these films were catalysed by SiO2 (silica) molecules from the glass reactor. Note:  In the Hadean breakdown of olivine to serpentinite as sea water reacted with ultramafic lavas would have released abundant silica. Serpentinisation also generates hydrogen. Intimate release of gas formed bubbles to create the spherical and polyp-like ‘protocells’. The authors imagine the Hadean global ocean permanently teeming with such microscopic receptacles. Such a veritable ‘primordial soup’ would be able to isolate other small molecules, such as amino acids, oligopeptides, nucleobases, and fatty acids, to generate more complex organic molecules in micro-reactors en route  to the kind of complex, self-sustaining systems we know as life.

So, is it possible to make a reasonable stab at what that first kind of life may have been? It was without doubt single celled. To reproduce it must have carried a genetic code enshrined in DNA, which is unique not only to all species, but to individuals. The key to tracking down LUCA is that it represents the point at which the evolutionary trees of the fundamental domains of modern life life – eukarya (including animals, plants and fungi), bacteria, and archaea – converge to a single evolutionary stem. There is little point in using fossils to resolve this issue because only multicelled life leaves tangible traces, and the first of those was found in 2,100 Ma old sediments in Gabon (see: The earliest multicelled life; July 2010). The key is using AI to compare the genetic sequences of the hugely diverse modern biosphere. Modern molecular phylogenetics and computing power can discern from their similarities and differences the relative order in which various species and broader groups split from others. It can also trace the origins of specific genes that provides clues about earlier genetic associations. Given a rate of mutation the modern differences provide estimates of when each branching occurred. The most recent genetic delving has been achieved by a consortium based at various institutions in Britain, the Netherlands, Hungary and Japan  (Moody, E.R.R. and 18 others 2024. The nature of the last universal common ancestor and its impact on the early Earth system. Nature Ecology & Evolution, v.8, pages 1654–1666; DOI: 10.1038/s41559-024-02461-1).

Moody et al have pushed back the estimated age of LUCA to halfway through the Hadean, between 4.09 to 4.33 billion years (Ga), well beyond the geologically known age of the earliest traces of life (3.5 Ga). That age for LUCA in itself is quite astonishing: it could have been only a couple of hundred million years after the Moon-forming interplanetary collision. Moreover, they have estimated that Darwin’s Ur-organism had a genome of around 2 million base pairs that encoded about 2600 proteins: roughly comparable to living species of bacteria and archaea, and thus probably quite advanced in evolutionary terms. The gene types probably carried by LUCA suggest that it may have been an anaerobic acetogen; i.e. an organism whose metabolism generated acetate (CH3COO−) ions. Acetogens may produce their own food as autotrophs, or metabolise other organisms (heterotrophs). If LUCA was a heterotroph, then it must have subsisted in an ecosystem together with autotrophs which it consumed, possibly by fermentation. To function it also required hydrogen that can be supplied by the breakdown of ultramafic rocks to serpentinites, which tallies with the likely ocean-world with ultramafic igneous crust of the Hadean (see the earlier paragraphs about protocells). If an autotroph, LUCA would have had an abundance of CO2 and H2 to sustain it, and may have provided food for heterotrophs in the early ecosystem. The most remarkable possibility discerned by Moody et al is that LUCA may have had a kind of immune system to stave off viral infection.

The carbon cycle on the Hadean Earth (Credit: Moody et al. 2024; Figure 3e)

The Hadean environment was vastly different to that of modern times: a waterworld seething with volcanism; no continents; a target for errant asteroids and comets; more rapidly spinning with a 12 hour day; a much closer Moon and thus far bigger tides. The genetic template for the biosphere of the following four billion years was laid down then. LUCA and its companions may well have been unique to the Earth, as are their descendants. It is hard to believe that other worlds with the potential for life, even those in the solar system, could have followed a similar biogeochemical course. They may have life, but probably not as we know it  . . .

See also: Ball, P. 2025. Luca is the progenitor of all life on Earth. But its genesis has implications far beyond our planet. The Observer, 19 January 2025.

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

Multiple Archaean gigantic impacts, perhaps beneficial to some early life

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In March 1989 an asteroid half a kilometre across passed within 500 km of the Earth at a speed of 20 km s-1. Making some assumptions about its density, the kinetic energy of this near miss would have been around 4 x 1019 J: a million times more than Earth’s annual heat production and humanity’s annual energy use; and about half the power of detonating every thermonuclear device ever assembled. Had that small asteroid struck the Earth all this energy would have been delivered in a variety of forms to the Earth System in little more than a second – the time it would take to pass through the atmosphere. The founder of “astrogeology” and NASA’s principal geological advisor for the Apollo programme, the late Eugene Shoemaker, likened the scenario to a ‘small hill falling out of the sky’. (Read a summary of what would happen during such an asteroid strike).  But that would have been dwarfed by the 10 to 15 km impactor that resulted in the ~200 km wide Chicxulub crater and the K-Pg mass extinction 66 Ma ago. Evidence has been assembled for Earth having been struck during the Archaean around 3.6 billion years (Ga) ago by an asteroid 200 to 500 times larger: more like four Mount Everests ‘falling out of the sky’ (Drabon, N. et al. 2024. Effect of a giant meteorite impact on Paleoarchean surface environments and life. Proceedings of the National Academy of Sciences, v. 121, article e2408721121; DOI: 10.1073/pnas.2408721121

Impact debris layer in the Palaeoarchaean Barberton greenstone belt of South Africa, which contains altered glass spherules and fragments of older carbonaceous cherts. (Credit: Credit: Drabon, N. et al., Appendix Fig S2B)

In fact the Palaeoarchaean Era (3600 to 3200 Ma) was a time of multiple large impacts. Yet their recognition stems not from tangible craters but strata that contain once glassy spherules, condensed from vaporised rock, interbedded with sediments of Palaeoarchaean ‘greenstone belts’ in Australia and South Africa (see: Evidence builds for major impacts in Early Archaean; August 2002, and Impacts in the early Archaean; April 2014), some of which contain unearthly proportions of different chromium isotopes (see: Chromium isotopes and Archaean impacts; March 2003). Compared with the global few millimetres of spherules at the K-Pg boundary, the Barberton greenstone belt contains eight such beds up to 1.3 m thick in its 3.6 to 3.3 Ga stratigraphy. The thickest of these beds (S2) formed by an impact at around 3.26 Ga by an asteroid estimated to have had a mass 50 to 200 times that of the K-Pg impactor.

Above the S2 bed are carbonaceous cherts that contain carbon-isotope evidence of a boom in single-celled organisms with a metabolism that depended on iron and phosphorus rather than sunlight. The authors suggest that the tsunami triggered by impact would have stirred up soluble iron-2 from the deep ocean and washed in phosphorus from the exposed land surface, perhaps some having been delivered by the asteroid itself. No doubt such a huge impact would have veiled the Palaeoarchaean Earth with dust that reduced sunlight for years: inimical for photosynthesising bacteria but unlikely to pose a threat to chemo-autotrophs. An unusual feature of the S2 spherule bed is that it is capped by a layer of altered crystals whose shapes suggest they were originally sodium bicarbonate and calcium carbonate. They may represent flash-evaporation of up to tens of metres of ocean water as a result of the impact. Carbonates are less soluble than salt and more likely to crystallise during rapid evaporation of the ocean surface than would NaCl.   

Time line of possible events following a huge asteroid impact during the Palaeoarchaean. (Credit: Drabon, N. et al. Fig 8)

So it appears that early extraterrestrial bombardment in the early Archaean had the opposite effect to the Chicxulub impactor that devastated the highly evolved life of the late Mesozoic. Many repeats of such chaos during the Palaeoarchaean could well have given a major boost to some forms of early, chemo-autotrophic life, while destroying or setting back evolutionary attempts at photo-autotrophy.

See also: King, A. 2024. Meteorite 200 times larger than one that killed dinosaurs reset early life. Chemistry World 23 October 2024.

Evidence for Earth’s magnetic field 3.7 billion years ago

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If ever there was one geological locality that  ‘kept giving’ it would have to be the Isua supracrustal belt in West Greenland. Since 1971 it has been known to be the repository of the oldest known metasedimentary rocks, dated at around 3.7 Ga. Repeatedly, geochemists have sought evidence for life of that antiquity, but the Isua metasediments have yielded only ambiguous chemical signs. A more convincing hint emerged from iron-rich silica layers (jasper) in similarly aged metabasalts on Nuvvuagittuk Island in Quebec on the east side of Hudson Bay, Canada, which may be products of Eoarchaean sea-floor hydrothermal vents. X-ray micro-tomography and electron microscopy of the jaspers revealed twisted filaments, tubes, knob-like and branching structures up to a centimetre long that contain minute grains of carbon, phosphates and metal sufides, but the structures are made from hematite (Fe2O3­) so an inorganic formation is just as likely as the earliest biology. Isua’s most intriguing contribution to the search for the earliest life has been what look like stromatolites in a marble layer (see: Signs of life in some of the oldest rocks; September 2016). Such structures formed in later times on shallow sea floors through the secretion of biofilms by photosynthesising blue-green bacteria.

Structure of the Earth’s magnetosphere that deflects charged particles which form the solar wind. (Credit: Wikipedia Commons)

For life to form and survive depends on its complex molecules being protected from high-energy charged particles in the solar wind. In turn that depends on a strong geomagnetic field deflecting the solar wind as it does today, except for a small proportion that descend towards the poles and form aurora during solar mass ejections. In  visits to Isua in 2018 and 2019, geophysicists from the Massachusetts Institute of Technology, USA and Oxford University, UK drilled over 300 rock cores from metasedimentary ironstones (Nichols, C.I.O. and 9 others 2024. Possible Eoarchean records of the geomagnetic field preserved in the Isua Supracrustal Belt, southern West Greenland. Journal of Geophysics Research (Solid Earth), v. 129, article e2023JB027706; DOI: 10.1029/2023JB027706 Magnetisation preserved in the samples (remanent magnetism) suggest that it was formed by a geomagnetic field strength of at least 15 microtesla, similar to that which prevails today. The minerals magnetite (Fe3O4) and apatite (a complex phosphate) in the ironstones have been dated using U-Pb geochronometry and record a metamorphic event only slightly younger that the age of the Isua belt (3.69 and 3.63 Ga respectively). There is no sign of any younger heating above the temperatures that would reset the ironstones’ magnetisation. The Isua remanent magnetisation is at least 200 Ma older than that found in igneous rocks from north-eastern South Africa dated at between 3.2 to 3.45 Ga. So even in the Eoarchaean it seems likely that life, had it formed, would have avoided the hazard of exposure to the high energy solar wind. In all likelihood, however, in a shallow marine environment it would have had to protect itself somehow from intense ultraviolet radiation. That is now vastly reduced by stratospheric ozone (O3) which could only form once the atmosphere had appreciable oxygen (O2) content, i.e. after the Great Oxygenation Event beginning about 2.4 Ga ago. Undoubted stromatolites as old as 3.5 Ga suggest that early photosynthesising bacteria clearly had cracked the problem of UV protection somehow.

Snowball Earth and the rise of multi-celled life

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You can follow my ‘reportage’ on the long running story of the Snowball Earth events during the Neoproterozoic Cryogenian Period (850 to 635 Ma) since 2000 through the index to annual Palaeoclimatology logs (15 posts). Once these dramatic events were over sedimentary rocks deposited around the world during the Ediacaran Period (635 to 541 Ma) record the sudden appearance of large-bodied fossils: the first multicellular animals. This explosion from slimy biofilms and colonies of single-celled prokaryotes and eukaryotes laid the basis for the myriad ecological niches that have characterised Planet Earth ever since. The change saw specialised eukaryote cells (see: The rise of the eukaryotes; December 2017), whose precursors had originated in single-celled forms, begin to cooperate inthe development of complex tissues, organs, and organ systems to form bodies rather than just cell walls. The pulsating evolution, diversification and repeated extinction that followed during the last one tenth of geological time shaped a planet that is unique in the Solar System and possibly in the galaxy, if not the entire universe. The simple biosphere that preceded it, on the other hand, may have emerged on innumerable rocky planets blessed with liquid water to survive little changed for billions of years, as have Earths’ prokaryotes, the Archaea and Bacteria.  

Artist’s impression of the Ediacaran Fauna (credit: Science)

The Ediacaran biological revolution followed repeated changes in the geochemistry of the oceans, which carbon isotope data from the Cryogenian and Ediacaran suggest to have ‘gone haywire’. This turmoil involved dramatic changes in the cycling of sulfur and phosphorus that help ‘fertilise’ the marine food chain and in the production of oxygen by photosynthesis that is essential for metazoan animals.  The episodes when the Earth was iced over reduced the availability of nutrients through decreased rates of ocean-floor burial of dead organisms. Such Snowball events would also have reduced penetration of sunlight in the oceans. Less photosynthesis would not only have reduced oxygen production but also the amounts of autotrophic organisms. Furthermore, decreased water temperature would have increased its viscosity thereby slowing the spread of nutrients. The food chain for heterotrophs was decimated. Each Snowball event ended with warming, ice-free conditions so that the marine biosphere could burgeon

A great deal of data and numerous theories have accumulated since the Snowball concept was first mooted, but there has been little progress in understanding the rise of multi-celled life. Four geoscientists from the Massachusetts Institute of Technology, the Santa Fe Institute and the University of Colorado (Boulder), USA have developed an interesting hypothesis for how this enormous evolutionary step may have developed (Crockett, W.W. et al. 2024. Physical constraints during Snowball Earth drive the evolution of multicellularity. Proceedings of the Royal Society B: Biological Sciences, v. 291; DOI: 10.1098/rspb.2023.2767). The concatenation of huge events during the Cryogenian and Ediacaran presented continually changing patterns of selective pressures on simple organisms that preceded that time period. Crockett et al. review them in the light of fundamental biology to suggest how multicellular animals emerged as the Ediacara Fauna. Intuitively, such harsh conditions suggest at worst mass, even complete, extinction, at best a general reduction in size of all organism to cope with scarce resources. That the size of eukaryotes should have grown hugely goes against the grain of most biologists’ outlook.

The authors consider the crucial factor to be fundamental differences between prokaryotes and early eukaryotes. Prokaryote cells are very small, and whether autotrophs of heterotrophs they absorb nutrients through their walls by diffusion. Single-celled eukaryotes are far larger than prokaryotes and typically have a flagellum or ‘tail’ so that they can move independently and more easily gather resources. Crockett et al. used computer modelling to simulate the type of life form that could grow and thrive under Snowball conditions. They found that prokaryotes could only grow smaller, being ‘stunted’ by scarce resources. On the other hand eukaryotes would be better equipped to gather resources, the more so if they adopted a simple multicellular form – a hollow, self-propelled sphere about the size of a pea, which the authors dub a choanoblastula. Although no such form is known today, it does resemble the green Volvox algae, and plausibly could have evolved further to the simple forms of the Ediacaran fauna. The next task is either to find a fossil of such an organism, or to grow one.

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.

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.

Darwin’s ‘warm little pond’: a new discovery

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There may still be a few people around today who, like Aristotle did, reckon that frogs form from May dew and that maggots and rats spring into life spontaneously from refuse. But the idea that life emerged somehow from the non-living is, to most of us, the only viable theory. Yet the question, ‘How?’, is still being pondered on. Readers may find Chapter 13 of Stepping Stones useful. There I tried to summarise in some detail most of the modern lines of research. But the issue boils down to means of inorganically creating the basic chemical building blocks from which life’s vast and complex array of molecules might have been assembled. Living materials are dominated by five cosmically common elements: carbon, hydrogen, oxygen, nitrogen and phosphorus – CHONP for short. Organic chemists can readily synthesise countless organic compounds from CHONP. And astronomers have discovered that life is not needed to assemble the basic ingredients: amino acids, carbon-ring compounds and all kinds of simpler CHONP molecules occur in meteorites, comets and even interstellar molecular clouds. So an easy way out is to assume that such ingredients ended up on the early Earth simply because it grew through accretion of older materials from the surrounding galaxy. Somehow, perhaps, their mixing in air, water and sediments together with a kind of chaotic shuffling did the job, in the way that an infinity of caged monkeys with access to typewriters might eventually create the entire works of William Shakespeare.  But, aside from the statistical and behavioural idiocy of that notion, there is a real snag: the vaporisation of the proto-Earth’s outer parts by a Moon-forming planetary collision shortly after initial accretion.

In 1871 Charles Darwin suggested to his friend Joseph Hooker that:

          ‘… if (and Oh, what a big if) we could conceive in some warm little pond, with all sorts of ammonia and phosphoric salts, light, heat, electricity, etc., present that a protein compound was chemically formed, ready to undergo still more complex changes, at the present day such matter would be instantly devoured or absorbed, which would never have been the case before living creatures were formed’.

Followed up in the 1920s by theorists Alexander Oparin and J.B.S. Haldane, a similar hypothesis was tested practically by Harold Urey and Stanley Miller at the University of Chicago. They devised a Heath-Robinson simulation of an early atmosphere and ocean seeded with simple CHONP (plus a little sulfur) chemicals, simmered it and passed electrical discharges through it for a week. The resulting dark red ‘soup’ contained 10 of the 20 amino acids from which a vast array of proteins can be built. A repeat in 1995 also yielded two of the four nucleobases at the heart of DNA – adenine and guanine.  But simply having such chemicals around is unlikely to result in life, unless they are continually in close contact: a vessel or bag in which such chemicals can interact. The best candidates for such a containing membrane are fatty acids of a form known as amphiphiles. One end of an amphiphile chain has an affinity for water molecules, whereas the other repels them. This duality enables layers of them, when assembled in water, spontaneously to curl up to make three dimensional membranes looking like bubbles. In the last year they too have been created in vitro (Purvis, G. et al. 2024. Generation of long-chain fatty acids by hydrogen-driven bicarbonate reduction in ancient alkaline hydrothermal vents. Nature Communications (Earth & Environment), v. 5, article 30; DOI: 10.1038/s43247-023-01196-4).

Cell-like membranes formed by fatty acid amphiphiles

Graham Purvis and colleagues from Newcastle University, UK allowed three very simple ingredients – hydrogen and bicarbonate ions dissolved in water and the iron oxide magnetite (Fe3O4) – to interact. Such a simple, inorganic mixture commonly occurs in hydrothermal vents and hot springs. Bicarbonate ions (HCO3–) form when CO2 dissolves in water, the hydrogen and magnetite being generated during the breakdown of iron silicates (olivines) when  ultramafic igneous rocks react with water:

3Fe2SiO4 + 2H2O → 2 Fe3O4 + 3SiO­2 +3H2

Various simulations of hydrothermal fluids had previously been tried without yielding amphiphile molecules. Purvis et al. simplified their setup to a bicarbonate solution in water that contained dissolved hydrogen – a simplification of the fluids emitted by hydrothermal vents – at 16 times atmospheric pressure and a temperature of 90°C. This was passed over magnetite. Under alkaline conditions their reaction cell yielded a range of chain-like hydrocarbon molecules. Among them was a mixture of fatty acids up to 18 carbon atoms in length. The experiment did not incorporate P, but its generation of amphiphiles that can create cell-like structures are but a step away from forming the main structural components of cell membranes, phospholipids.

When emergence of bag-forming membranes took place is, of course, hard to tell. But in the oldest geological formations ultramafic lava flows are far more common than they are today. In the Hadean and Eoarchaean, even if actual mantle rocks had not been obducted as at modern plate boundaries, at the surface there would have been abundant source materials for the vital amphiphiles to be generated through interaction with water and gases: perhaps in ‘hot little ponds’. To form living, self-replicating cells requires such frothy membranes to have captured and held amino acids and nucleobases. Such proto-cells could become organic reaction chambers where chemical building blocks continually interacted, eventually to evolve the complex forms upon which living cells depend.

Why did the largest ever primate disappear?

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Chinese apothecary shops sell an assortment of fossils. They include shells of brachiopods that when ground up and dissolved in water allegedly treat rheumatism, skin diseases, and eye disorders. Traditional apothecaries also supply  ‘dragons’ teeth’, said by Dr Subhuti Dharmananda, Director of the Institute for Traditional Medicine in Portland, Oregon to treat epilepsy, madness, manic running about, binding qi (‘vital spirit’) below the heart, inability to catch one’s breath, and various kinds of spasms, as well as making the body light, enabling one to communicate with the spirit light, and lengthening one’s life. Presumably have done a roaring trade in ‘dragons’ teeth’ since they were first mentioned in a Chinese pharmacopoeia (the Shennong Bencao Jing) from the First Century of the Common Era. In 1935 the anthropologist Gustav von Koenigswald came across two ‘dragons’ teeth’ in a Hong Kong shop. They were unusually large molars and he realised they were from a primate, but far bigger (20  × 22 mm) than any from living or fossil monkeys, apes or humans.

Eventually, in 1952 (he had been interned by Japanese forces occupying Java), von Koenigswald formally described the teeth and others that he had found. Their affinities and size prompted him to call the former bearer the ‘Huge Ape’ (Gigantopithecus). By 1956 Chinese palaeontologists had tracked down the cave site in Guangxi province where the teeth had been sourced, and a local farmer soon unearthed a complete lower jawbone (mandible) that was indeed gigantic. More teeth and mandibles have since been found at several sites in Southern and Southeast Asia, with an age range from about 2.0 to 0.3 Ma. Anatomical differences between teeth and mandibles suggest that there may have been 4 different species. Using mandibles as a very rough guide to overall size it has been estimated that Gigantopithecus may have been up to 3 m tall weighing almost 600kg.

Above: Size comparison of G. blacki with a 1.8 m tall human male; NB G.blacki probably walked on all fours, as do living orangutans when they rarely descend from the forest canopy. (Credit: Frido Welker) Below: Mandible of Gigantopithecus blacki from India (Credit: Prof. Wei Wang, Photo retouched by Theis Jensen)

Plaque on some teeth contain evidence for fruit, tubers and roots, but not grasses, which suggest suggest that Gigantopithecus had a vegetarian diet based on forest plants. Mandibles also showed affinities with living and fossil orangutans (pongines). Analysis of proteins preserved in tooth enamel confirm this relationship (Welker, F. and 17 others 2019. Enamel proteome shows that Gigantopithecus was an early diverging pongine. Nature, v.576, p. 262–265; DOI: 10.1038/s41586-019-1728-8). It was one of the few members of the southeast Asian megafauna to go extinct at the genus level during the Pleistocene. Its close relative Pongo the orangutan survives as three species in Borneo and Sumatra. Detailed analysis of material from 22 southern Chinese caves that have yielded Gigantopithecus teeth has helped resolve that enigma (Zhang, Y. and 20 others 2024. The demise of the giant ape Gigantopithecus blacki. Nature, v. 625; DOI: 10.1038/s41586-023-06900-0).

At the time Gigantopithecus first appeared in the geological record of China (~2.2 Ma), it ranged over much of south-western China. The early Pleistocene ecosystem there was one of diverse forests sufficiently productive to support large numbers of this enormous primate and also the much smaller orangutan Pongo weidenreichi.  By 295 to 215 ka, the age of the last known Gigantopithecus fossils, its range had shrunk dramatically. The teeth show marked increases in size and complexity by this time, which suggests adaptation of diet to a changing ecosystem. That is confirmed by pollen analysis of cave sediments which reveal a dramatic decrease in forest cover and increases in fern and non-arboreal flora at the time of extinction. One physical sign of environmental stress suffered by individual late G. blacki is banding in their teeth defined by large fluctuations of barium and strontium concentrations relative to calcium. The bands suggest that each individual had to change its diet repeatedly over its lifetime. Closely related orangutans, on the other hand survived into the later Pleistocene of China, having adapted to the changed ecosystem, as did early humans in the area. It thus seems likely that Gigantopithecus was an extreme specialist as regards diet, and was unable to adapt to changes brought on by the climate becoming more seasonal. Today’s orangutans in Indonesia face a similar plight, but that is because they have become restricted to forest ‘islands’ in the midst of vast areas of oil palm plantations. Their original range seems to have been much the same as that of Gigantopithecus, i.e. across south-eastern Asia, but Pongo seems to have gone extinct outside of Indonesia (by 57 ka in China) during the last global cooling and when forest cover became drastically restricted.

When giant worms roamed the seas!

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At the start of the Cambrian Period animal life began to diversify from that of the Ediacaran world. For the first time sediments on the seafloor were explored for sustenance, leading to a variety of burrows that disrupted fine depositional layers. The basal Cambrian sandstones found in Britain and elsewhere are pervasively bioturbated: good evidence for the start of a ‘Worm world’ that marks the Precambrian-Phanerozoic boundary. That is probably a misnomer for the shallow seabed of that time, as fossils of burrowers with a variety of hard parts turn up in the oldest Cambrian sequences. Also appearing for the first time are tooth-like microfossils that took on such a range of bizarre shapes that they have long been used for correlating sedimentary strata in the absence of larger creatures. Some of these conodonts have been attributed to early vertebrates akin to modern lampreys and hag fish, but others may have been the grasping mouth-spines of a group of predatory worms which also survive to the present: chaetognaths. Apart from these oral spines chaetognaths lack hard parts, so anatomical details of ancient ones are only found in sites of exquisite preservation or lagerstätten. In such rare, tranquil places soft tissues such as muscles may be preserved by phosphatisation during decay.

Reconstruction of Timorebestia koprii showing its musculature, nerve system and mouthparts, It probably propelled itself by fluttering its outer and rear flaps, much like a modern flatfish. Credit: Park et al., Fig 4

One of the earliest Phanerozoic lagerstätten (Sirius Passet) occurs in northern Greenland. It is curiously named after the Sirius Dog Sled Patrol, an elite pair of naval troops with a sledge and 12 dogs that enforces Danish sovereignty over the Greenlandic shore of the Arctic Ocean. The Sirius Passet fauna includes a monstrous chaetognath over 30 cm long (Park, T.-Y. S. and 12 others 2024. A giant stem-group chaetognath. Science Advances, v. 10 article eadi6678; DOI: 10.1126/sciadv.adi6678). It is called Timorebestia koprii (Timorebestia is Latin for ‘terror beast’) and was related to the living, but tiny, arrow worms that prey on zooplankton in modern oceans. This description and moniker may seem to be somewhat hyperbolic, but Timorobestia outranks in size any Early Cambrian predatory arthropods. It was probably high in the Early Cambrian trophic pyramid, but was soon relegated by the later Cambrian rise of trilobites and then of cephalopods and eventually jawed vertebrate fishes in the Silurian. One specimen contained shells of a swimming arthropod whose protective spines did not deter the ‘terrible’ chaetognath from swimming them down.

See also: ‘Giant’ predator worms more than half a billion years old discovered in North Greenland. Science Daily, 3 January 2024.

Repeated climate and ecological stress during the run-up to the K-Pg extinction

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The Cretaceous-Palaeogene mass extinction is no longer an event that polarises geologists’ views between a slow volcanic driver (The Deccan large igneous province) and a near instantaneous asteroid impact (Chicxulub). There is now a broad consensus that both processes were involved in weakening the Late Cretaceous biosphere and snuffing out much of it around 66 Ma ago. Yet is still no closure as regards the details. From a palaeontologist’s standpoint the die-off varied dramatically between major groups of animals. For instance, the non-avian dinosaurs disappeared completely while those that evolved to modern birds did not. Crocodiles came through it largely unscathed unlike aquatic dinosaurs. In the seas those animals that lived in the water column, such as ammonites, were far more affected than were denizens of the seafloor. But much the same final devastation was visited on every continent and ocean. However, lesser and more restricted extinctions occurred before the Chicxulub impact.

Scientists from Norway, Canada, the US, Italy, the UK and Sweden have now thrown light on the possibility that climate change during the last half-million years of the Cretaceous may have been eroding biodiversity and disrupting ecosystems (Callegaro, S. et al. 2023. Recurring volcanic winters during the latest Cretaceous: Sulfur and fluorine budgets of Deccan Traps lavas. Science Advances, v. 9, article eadg8284; DOI: 10.1126/sciadv.adg8284). Almost inevitably, they turned to the record of Deccan volcanism that overlapped the K-Pg event, specifically the likely composition of the gases that the magmas may have belched into the atmosphere. Instead of choosing the usual suspect carbon dioxide and its greenhouse effect, their focus was on sulfur and fluorine dissolved in pyroxene grains from 15 basalts erupted in the 10 Formations of the Deccan flood-basalt sequence. From these analyses they were able to estimate the amounts of the two elements in the magma erupted in each of these 10 phases.

Exposed section through a small part of the Deccan Traps in the Western Ghats of Maharashtra, India. (Credit: Gerta Keller, Princeton University)

The accompanying image of a famous section through the Deccan Traps SE of Mumbai clearly shows that 15 sampled flows could reveal only a fraction of the magmas’ variability: there are 12 flows in the foreground alone. The mountain beyond shows that the pale-coloured sequence is underlain by many more flows, and the full Deccan sequence is about 3.5 km thick. Clearly, flood-basalt volcanism is in no way continuous, but builds up from repeated lava flows that can be as much as 50 m thick. Each of them is capped by a red, clay-rich soil or bole – from the Greek word bolos (βόλος) meaning ‘clod of earth’. Weathering of basalt would have taken a few centuries to form each bole. Individual Deccan flows extend over enormous areas: one can be traced for 1500 km. At the end of volcanism the pile extended over roughly 1.5 million km2 to reach a volume of half a million km3.

Fluorine is a particularly toxic gas with horrific effects on organisms that ingest it. In the form of hydrofluoric acid (HF) – routinely used to dissolve rock – it penetrates tissue very rapidly to react with calcium in the blood to form calcium fluoride. This causes very severe pain, bone damage and other symptoms of skeletal fluorosis. The 1783-4 eruption of the Laki volcanic fissure in Iceland emitted an estimated 8,000 t of HF gas that wiped out more than half the domestic animals as a result of their eating contaminated grass. The famine that followed the eruption killed 20 to 25% of Iceland’s people: exhumed human skeletons buried in the aftermath show the distinctive signs of endemic skeletal fluorosis. This small flood-basalt event had global repercussions, as the Wikipedia entry for Laki documents. Volcanic sulfur emissions in the form of SO2 gas react with water vapour to form sulphuric acid aerosols in a reflective haze. If this takes place in the stratosphere as a result of powerful eruptions, as was the case with the 1991 Pinatubo eruption in the Philippines, the high-altitude haze lingers and spreads. This results in reduced solar warming: a so-called ‘volcanic winter’. In the Pinatubo aftermath global temperatures fell by about 0.5°C during 1991-3. Unsurprisingly, volcanic sulfur emissions also result in acid rainfall. Moreover, inhaling the sulphur-rich haze at low altitudes causes victims to choke as their respiratory tissues swell: an estimated 23,000 people in Britain died in this way when the 1783-4 Laki eruption haze spread southwards Sara Calegaro and colleagues found that the fluorine and sulfur contents of Deccan magmas fluctuated significantly during the eruptive phases. They suggest that fluorine emissions were far above those from Laki, perhaps leading to regional fluorine toxicity around the site of the Deccan flood volcanism but not extinctions. Global cooling due to sulphuric acid aerosols in the stratosphere is suggested to have happened repeatedly, albeit briefly, as eruption waxed and waned during each phase. Magmas rich in volatiles would have been more likely to erupt explosively to inject SO2 to stratospheric altitudes (above 10 to 20 km). The authors do not attempt to model when such cooling episodes may have occurred: data from only 15 levels in the Deccan Traps do not have the time-resolution to achieve that. They do, however, show that this large igneous province definitely had the potential to generate ‘volcanic winters’ and toxic episodes. Time and time again ecosystems globally and regionally would have experienced severe stress, the most important perhaps being disruption of the terrestrial and marine food chains.