Category Archives: Geobiology, palaeontology, and evolution

The late-Ordovician mass extinction: volcanic connections

The dominant feature of Phanerozoic stratigraphy is surely the way that many of the formally named major time boundaries in the Stratigraphic Column coincide with sudden shifts in the abundance and diversity of fossil organisms. That is hardly surprising since all the globally recognised boundaries between Eras, Periods and lesser divisions in relative time were, and remain, based on palaeontology. Two boundaries between Eras – the Palaeozoic-Mesozoic (Permian-Triassic) at 252 Ma and Mesozoic-Cenozoic (Cretaceous-Palaeogene) at 66 Ma – and a boundary between Periods – Triassic-Jurassic at 201 Ma – coincide with enormous declines in biological diversity. They are defined by mass extinctions involving the loss of up to 95 % of all species living immediately before the events. Two other extinction events that match up to such awesome statistics do not define commensurately important stratigraphic boundaries. The Frasnian Stage of the late-Devonian closed at 372 Ma with a prolonged series of extinctions (~20 Ma) that eliminated  at least 70% of all species that were alive before it happened. The last 10 Ma of the Ordovician period witnessed two extinction events that snuffed out about the same number of species. The Cambrian Period is marked by 3 separate events that in percentage terms look even more extreme than those at the end of the Ordovician, but there are a great many less genera known from Cambrian times than formed fossils during the Ordovician.

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Faunal extinctions during the Phanerozoic in relation to the Stratigraphic Column.

Empirical coincidences between the precise timing of several mass extinctions with that of large igneous events – mainly flood basalts – suggest a repeated volcanic connection with deterioration of conditions for life. That is the case for four of the Famous Five, the end-Ordovician die-off having been ascribed to other causes; global cooling that resulted in south-polar glaciation of the Gondwana supercontinent and/or an extra-solar gamma-ray burst (predicated on the preferential extinction of Ordovician near-surface, planktonic fauna such as some trilobite families). Neither explanation is entirely satisfactory, but new evidence has emerged that may support a volcanic trigger (Jones, D.S. et al. 2017. A volcanic trigger for the Late Ordovician mass extinction? Mercury data from south China and Laurentia. Geology, v. 45, p. 631-634; doi:10.1130/G38940.1). David Jones and his US-Japan colleagues base their hypothesis on several very strong mercury concentrations in thin sequences in the western US and southern China of late Ordovician marine sediments that precede, but do not exactly coincide with, extinction pulses. They ascribe these to large igneous events that had global effects, on the basis of similar Hg anomalies associated with extinction-related LIPs. Yet no such volcanic provinces have been recorded from that time-range of the Ordovician, although rift-related volcanism of roughly that age has been reported from Korea. That does not rule out the possibility as LIPs, such as the Ontong Java Plateau, are known from parts of the modern ocean floor that formed in the Mesozoic and Cenozoic. Ordovician ocean floor was subducted long ago.

The earlier Hg pulses coincide with evidence for late Ordovician glaciations over what is now Africa and eastern South America. The authors suggest that massive volcanism may then have increased the Earth’s albedo by blasting sulfates into the stratosphere. A similar effect may have resulted from chemical weathering of widely exposed flood basalts which draws down atmospheric CO2. The later pulses coincide with the end of Gondwanan glaciation, which may signify massive emanation of volcanic CO2 into the atmosphere and global warming. Despite being somewhat speculative, in the absence of evidence, a common link between the Big Five plus several other major extinctions and LIP volcanism would quieten their popular association with major asteroid and/or comet impacts currently being reinvigorated by drilling results from the K-Pg Chicxulub crater offshore of Mexico’s Yucatan Peninsula.

Earliest hydrothermal vents and evidence for life

 

That seawater circulates through the axial regions of rifts associated with sea-floor spreading has been known since well before the acceptance of plate tectonics. The idea stems from the discovery in 1949 of brines with a temperature of 60°C on the central floor of the Red Sea, which in the early 60s turned out to be anomalously metal-rich as well. Advanced submersibles that can withstand the high pressures at great depth a decade later produced images of swirling clouds of sediment from large sea-floor springs, first on the Galapagos rift and subsequently on many others. The first shots were of dark, turbulent clouds, prompting the term ‘black smoker’ for such hydrothermal vents and it turns out that others produce light-coloured clouds – ‘white smokers’. Sampling revealed that the sediments in black smokers were in fact fine-grained precipitates of metallic sulfides, whereas those forming white smokers were sulfates, carbonates and oxides of barium calcium and silicon also precipitated from solute-rich brines produced by partial dissolution of ocean floor through which they had passes.

A black smoker known as "the brothers".

A black smoker with associated organism. (credit: Wikipedia)

Excitement grew when hydrothermal vents were shown to have complex animal ecosystems completely new to science. A variety of chemical evidence, most importantly the common presence of proteins and other cell chemicals built around metal sulfide groups in most living organisms, prompted the idea that hydrothermal vents may have hosted the origins of life on Earth. Many fossil vent systems also contain fossils; macrofossils in the Phanerozoic and microbial ones from the Precambrian. But tangible signs of life, in the form of mats ascribed to bacteria or archaea holding together fine-grained sediments, go back no further than 3830 Ma in the Isua area of SW Greenland. Purely geochemical evidence that carbonaceous compounds may have formed in living systems  are ambiguous since quite complex hydrocarbons can be synthesised abiogenically by Fischer-Tropsch reactions between carbon monoxide and hydrogen. Signs of deep sea hydrothermal activity are common in any geological terrain containing basalt lavas with the characteristic pillows indicating extrusion beneath water. So to trace life’s origins all that is needed to trigger the interest of palaeobiologists are the oldest known pillow lavas. Until quite recently, that meant the Isua volcano-sedimentary association, but heating, high pressures and  very strong deformation affected those rocks when they were metamorphosed half a billion years after they were formed; a cause for skepticism by some geoscientists.

The primacy of Isua metavolcanic rocks has been challenged by more extensive metamorphosed basalts in the Nuvvuagittuk area in Quebec on the east side of Hudson Bay, Canada. They contain hydrothermal ironstones associated with pillowed basalts that are cut by more silica-rich intrusive igneous rocks dated between 3750 and 3775 Ma. That might place the age of basalt volcanism and the hydrothermal systems in the same ball park as those of Isua, but intriguingly the basalts’ 146Sm-142Nd systematics suggest a possible age of magma separation from the mantle of 4280 Ma (this age is currently disputed as it clashes with  U-Pb dates for zircon grains extracted from the metabasalts around the same as the age at Isua). Nonetheless, some parts of the Nuvvuagittuk sequence are barely deformed and show only low-grade metamorphism, and they contain iron- and silicon-rich hot spring deposits (Dodd, M.S. et al. 2017. Evidence for early life in Earth’s oldest hydrothermal vent precipitates. Nature, v. 543, p. 60-64; doi:10.1038/nature21377). As at Isua, the ironstones contain graphite whose carbon isotope proportions have an ambiguous sign of having formed by living or abiotic processes. It is the light deformation and low metamorphism of the rocks that gives them an edge as regards being hosts to tangible signs of life. Extremely delicate rosettes and blades of calcium carbonate and phosphate, likely formed during deposition, remain intact. These signs of stasis are in direct contact with features that are almost identical to minute tubes and filaments formed in modern vents by iron-oxidising bacteria. All that is missing are clear signs of bacterial cells. Ambiguities in the dating of the basalt host rocks do not allow the authors claims that their signs of life are significantly older than those at Isua, but their biotic origins are less open to question. Neither offer definitive proof of life, despite widespread claims by media science correspondents, some of whom tend  metaphorically to ‘run amok ‘ when the phrase ‘ancient life’ appears; in this case attempting to link the paper with life on Mars …

You can find more on early life here

 

Dinosaurs in the flesh and feathers

Until only a few decades ago artistic portrayals of dinosaurs had them as leathery and scaled like lizards or crocodiles, as indeed rare examples of their fossilized skin seemed to suggest. The animatronic and CGI dinosaurs of the first Jurassic Park film were scary, but brownish grey. Later films in the franchise had them mottled and sometimes in colour, but still as mainly scaled leathery monsters. Reality soon overtook imagination as more and more exquisitely preserved fossils of small species were turned up, mainly in China, that were distinctly furry, fuzzy or feathered as shown below in a Microraptor gui fossil. It is now well-established that birds arose in the Jurassic from saurischian  dinosaurs, the order that also included all of the large carnivorous dinosaurs as well as the many more nimble and diminutive ones whose feathers sometimes conferred an ability to glide or fly. Even the other main order, the ornithischia noted for hugeness and herbivory, has yielded fossil skin that suggest furry or feathered pelts. Once fur and feathers had been found, the next big issue became whether or not dinosaurs may have been as gaudy as many modern birds.

 

Fossil of a feathered dinosaur Microraptor gui from the early Cretaceous Jiufotang Formation in China (source: Wikipedia)

Fossil of a feathered dinosaur Microraptor gui from the early Cretaceous Jiufotang Formation in China (source: Wikipedia)

One of the first palaeobiologists to become immersed in the search for colourful dinosaurs was Jakob Vinther, now of Britain’s Bristol University. In The March 2017 issue of Scientific American he summarises the progress that he and his colleagues have made (Vinther, J. 2017. The true colors of dinosaurs. Scientific American, v. 316(3), p. 42-49). On his account, the major breakthrough was Vinther’s discovery of tiny spherules in fossilised octopus ink that were identical to the granules of the pigment melanin that give the famous cephalopod ‘smoke screen’ its brownie-black colour. Melanin, or more precisely the melanosomes in which it is enclosed, is a key to coloration throughout much of the animal kingdom, especially in fur and feathers. There are two basic kinds, one conferring blackness and the other that imparts a rusty red hue, which combined with paleness due to lack of melanin together produce a gamut of greys, reds, browns oranges and yellows.  Elongated melanosomes when lined up produce the phenomenon of interference fringes that yield iridescence, responsible for the bright colours of starlings, hummingbirds and some ducks when in bright light. There are other pigments, such as carotenoids (bright reds and yellows) and porphyrins (green, red and blue) that add to the gamut possible in animals, but it was melanosomes that captured Vinther’s attention because of their importance in living feather colours.

Melanosomes occur in distinctively grouped assemblages, according to actual colour, and very similar microscopic structures turned up in the first fossil bird feathers that he studied. Others had assumed that they were bacterial colonies, which had grown during decay. The breakthrough was finding a fossil bird feather in which different structures were arranged in stripes; clear signs of patterning. Vinther’s concept bears fruit in a range of furry and feathered dinosaurs. One (Anchiornis) with a black and white body and limb speckles had a bright red crest and another (Sinosauropterix) was ginger over its back with a tiger striped tail and a white underside; an example of countershaded camouflage. His team has even been able to assign different kinds of patterning to a variety of possible habitats. Given superbly preserved specimens it seems likely that dinosaur and bird coloration may be traceable back more than 200 Ma.

English: Illustration of the small theropod di...

Artist’s impression of the small theropod dinosaur Microraptor showing colours predicted by analysis of melanosomes on its feathers.(credit: Wikipedia)

Another aspect of the filmic licence of Jurassic Park was its hinging on preservation of genetic material from the Mesozoic, specifically in a parasite preserved in amber, so that the creatures could be resurrected by bio-engineering. The only relevant find is a 46 Ma old mosquito whose abdomen was blood-engorged when it was fossilised. But all that remains are high iron concentrations the organic molecule porphyrin; break-down products of haemoglobin. Given that fossil DNA can only be reassembled from millions of fragmentary strands found in fossils in digital form that corresponds to the order of AGCT nucleobases that is barely likely to be possible – the oldest full genome yet analysed is that of a 700 ka horse. However, another biological material that varies hugely among living animals, protein, has proved to be tractable, albeit in a very limited way. Frozen mammoth meat, somewhat bloody, is sometimes unearthed from Siberian permafrost, but according to one Russian mammoth expert even the best preserved is inedible.

Beyond the Pleistocene the search for fossilised proteins has been hesitant and deeply controversial, particularly in the case of that from dinosaurs, for the obvious reason of publicity suspicions. But again, it is a story of persistence and patience. Mary Schweitzer of North Carolina State University claimed in 2007 that she had found some, but was howled down by other palaeontologists on the issues of its unlikely survivability and contamination. But other researchers had pushed back the age limits. By repeating their earlier analyses with the greatest possible care Schweitzer’s team confirmed their earlier results with several strands of the protein collagen about 15 amino acids in length from an 80 Ma old duck-billed dinosaur. Moreover they were able to show a closer affinity of the partial proteins to those of modern birds than to other reptiles, tallying with tangible fossil evidence (Schroeter, E.R  and 8 others 2017. Expansion for the Brachylophosaurus canadensis Collagen I Sequence and Additional Evidence of the Preservation of Cretaceous Protein. Journal of Proteome Research, v. 16, p. 920-932). The work continues for other dinosaurs and early fossil birds, with better reason for confidence and a chance of tying-down genetic relatedness. Another approach shows that collagen may still be preserved in a Jurassic (195 Ma) sauropod dinosaur’s rib (Lee, Y-C. and 9 others 2017. Evidence of preserved collagen in an Early Jurassic sauropodomorph dinosaur revealed by synchrotron FTIR microspectroscopy. Nature Communications, v. 8 doi:10.1038/ncomms14220).

See also: Service, R.F. 2017. Researchers close in on ancient dinosaur remains. Science (News in depth), v. 355, p. 441- 442.

Earliest signs of vertebrates’ ancestor?

Studies of DNA among living animals suggest that our own group, the vertebrates of the phylum Chordata, originated from a common ancestor that we share with echinoderms (sea urchins, star fish, sea cucumbers etc) and one of many worm-like phyla. This superphylum comprises the deuterostomes, but it is just one of several that encompass all animals and happens to be one of the smallest in terms of the number of living species that belong to it. We deuterostomes are vastly outnumbered by arthropods, nematodes, other worm-like creatures, molluscs, the rest of the animal kingdom and, of course, single-celled organisms, plants and fungi. Yet the DNA-based Circle of Life reveals that the deuterostome ancestral spoke originated early on in animal evolution.

The ‘Circle of Life’ as compiled by Cody Hinchliffe of the University of Michigan and 21 collaborators from the USA, and partly based on Fischetti, M. 2016. The circle of life. Scientific American, v. 314 (March 2016).

The ‘Circle of Life’ as compiled by Cody Hinchliffe of the University of Michigan and 21 collaborators from the USA, and partly based on Fischetti, M. 2016. The circle of life. Scientific American, v. 314 (March 2016).

The majority of animals of all kinds are blessed with a mouth separate from means of expelling waste products and can be divided into two similar halves, hence their name bilaterians. The earliest fossils judged to be of this kind date to about 580 to 600 Ma ago, in the Doushantuo Formation of southern China, all of them visible only using microscopes. A DNA-based molecular clock hints at around 900-1000 Ma for the emergence of all animal body plans known today. Now another important time marker has turned up, again in sediments showing exquisite fossil preservation from China (Han, J. et al. 2017. Meiofaunal deuterostomes from the basal Cambrian of Shaanxi (China). Nature, v. 542, (online); doi: 10.1038/nature21072). The Chinese-British team of palaeontologists has found tiny, bag-like fossils preserved in phosphate, which have a mouth surrounded by folds and conical openings on either side of the body. They lived in limy muds on the sea bed now preserved as limestones at the base of the Cambrian System (541 Ma) and probably had a habit akin to worms in the most general sense. The authors sifted through 3 tonnes of rock to recover the fossils, rather than relying on a lucky hammer stroke.

Reconstruction of Saccorhytus coronarius from the lowest Cambrian of Shaanxi, China. (credit: Han et al 1917)

Reconstruction of Saccorhytus coronarius (diameter about 1 mm) from the lowest Cambrian of Shaanxi, China. (credit: Han et al 1917)

Not especially prepossessing, the fossils are said to show more affinity to deuterostomes than anything else and to be the earliest known fossil examples. Yet the world’s media pounced on them as the ‘earliest known human ancestors’, which is a bit rich as they could equally be the earliest sea urchins or may have led to several odd-looking fossils known only from the later Cambrian. It isn’t possible to say with any certainty that they lie on the path that led to chordates and thus ourselves. Of course, that would not raise headlines in newspapers of record, such as Britain’ Daily Telegraph, on the BBC News website or Fox News.  The authors are much more honest, claiming only that the Saccorhytus coronarius fossils are probably deuterostomes whose affinities and later descendants are obscure. Their most important conclusion is that the cradle of our branch of animals lay in deep water muds laid down around the Precambrian-Cambrian boundary, ideal for subtly varied small, flabby creatures behaving like worms.  Many more varieties are likely remain to be found in similar rocks of the late Precambrian and slightly younger Cambrian when they are studied painstakingly in microscopic detail. A start has been made, that’s all.

For more on early evolution see here and here

Amazonian forest through the last glacial maximum

Accelerated evolution may occur when a small population of a species – whose genetic variability is therefore limited – becomes isolated from all other members. This is one explanation for the rise of new species, as in the Galapagos archipelago. Creation of such genetic bottlenecks encourages rapid genetic drift away from the main population. It has been suggested to explain sudden behavioural shifts in anatomically modern humans over the last hundred thousand years or so, partly through rapid and long-distance migrations and partly through a variety of environmental catastrophes, such as the huge Toba eruption around 74 ka. Another example has been proposed for the teemingly diverse flora and fauna of the Amazon Basin, particularly among its ~7500 species of butterflies, which has been ascribed to shrinkage of the Amazonian rain forest to isolated patches that became refuges from dry conditions during the last glacial maximum.

Top: Arid ice age climate Middle: Atlantic Per...

Potential forest cover inferred from global climate models for the last glacial maximum (top) the Holocene thermal maximum and at present.. (credit: Wikipedia)

A great deal of evidence suggests that during glacial maxima global climate became considerably drier than that in interglacials, low-latitude deserts and savannah grasslands expanding at the expense of humid forest. Yet the emerging complexity of how climate change proceeds from place to place suggests that evidence such continental drying from one well-documented region, such as tropical Africa, cannot be applied to another without confirming data. Amazonia has been the subject of long-standing controversy about such ecological changes and formation of isolated forest ‘islands’ in the absence of definitive palaeoclimate data from the region itself. A multinational team has now published data on climatic humidity changes over the last 45 ka in what is now an area of dense forest but also receives lower rainfall than most of Amazonia; i.e. where rolling back forest to savannah would have been most likely to occur during the last glacial maximum (Wang, X. et al. 2017. Hydroclimate changes across the Amazon lowlands over the past 45,000 years. Nature, v. 541, p. 204-207; doi:10.1038/nature20787).

Their study area is tropical karst, stalagmites from one of whose caves have yielded detailed oxygen-isotope time series. Using the U/Th dating technique has given the data a time resolution of decades covering the global climatic decline into the last glacial maximum and its recovery to modern times. The relative abundance of oxygen isotopes (expressed by δ18O) in the calcium carbonate layers that make up the stalagmites is proportional to that of the rainwater that carried calcium and carbonate ions dissolved from the limestones. The rainwater δ18O itself depended on the balance between rainfall and evaporation, higher values indicating reduced precipitation. Relative proportions of carbon isotopes in the stalagmites, expressed by δ13C, record the balance of trees and grasses, which have different carbon-isotope signatures. Rainfall in the area did indeed fall during the run-up to the last glacial maximum, to about 60% of that at present, then to rise to ~142% in the mid-Holocene (6 ka). Yet δ13C in the stalagmites remained throughout comparable with those in the Holocene layers, its low values being incompatible with any marked expansion of grasses.

English: View of Amazon basin forest north of ...

Amazonian rain forest north of Manaus, Brazil. (credit: Wikipedia)

One important factor in converting rain forest to grass-dominated savannah is fire induced by climatic drying. Tree mortality and loss of cover accelerates drying out of the forest floor in a vicious circle towards grassland, expressed today by human influences in much of Amazonia. Fires in Amazonia must therefore have been rare during the last ice age; indeed sediment cores from the Amazon delta do not reveal any significant charcoal ‘spike’.

See also: Bush, M.B 2017. The resilience of Amazonian forests. Nature, v. 541, p. 167-168; doi:10.1038/541167a

K-T (K-Pg) boundary impact probed

One of the most eagerly followed ocean-floor drilling projects has just released some results. Its target is 46 km radially away from the centre of the geophysical anomaly associated with the Chixculub impact structure just to the north of Mexico’s Yucatan Peninsula. In the case of large lunar impact craters the centre is often surrounded by a ring of peaks. Modelling suggests such features are produced by the deep penetration of immense seismic shock waves. In the first minute these excavate and fling out debris to leave a cavity penetrating deep into the crust. Within three minutes the cavity walls collapse inwards creating a rebound superficially similar to the drop flung upwards after an object is dropped in liquid. This, in turn, collapses outwards to emplace smashed and partially melted deep crustal material on top of what were once surface materials, creating a crustal inversion beneath a mountainous ring of Himalayan dimensions that surrounds a by-now shallow crater. That is the story modelled from what is known about well-studied, big craters on the Moon and Mercury. Chixculub is different because the impact was into the sea and involved debris-charged tsunamis that finally plastered the actual impact scar with sediments. The drilling was funded for several reasons, some palaeontological others relating to the testing of theories of impact processes and their products. Chixculub is probably the only intact impact crater on Earth, and the first reports of findings are in the second category (Morgan, J.V. and 37 others 2016. The formation of peak rings in large impact craters. Science, v. 354, p. 878-882; doi: 10.1126/science.aah6561).

English: K/T extinction event theory. An artis...

Artist’s depiction of the Chicxulub impact 65 million years ago that many scientists say is the most direct cause of the dinosaurs’ disappearance (credit: Wikipedia)

The drill core, reaching down to about 1.3 km below the sea floor penetrates post-impact Cenozoic sediments into a 100 m thick zone of breccias containing fragments of impact melt rock, probably the infill of the central crater immediately following the first few minutes of impact. Beneath that are coarse grained granites representing the middle continental crust from original depths around 10 km. The granite is intensely fractured and riven by dykes and pods of impact melt, and contains intensely shocked grains that typify impacts that produce a transient pressure of ~60 GPa – around six hundred thousand times atmospheric pressure. From seismic reflection surveys this crustal material overlies as yet un-drilled Mesozoic sedimentary rocks. Its density is significantly less than that of unshocked granite – averaging 2.4 compared with 2.6 g cm3. So it is probably filled with microfractures and sufficiently permeable for water to have penetrated once the impact site had cooled. This poses the question, yet to be addressed in print, of whether or not this near-surface layer became colonised by microorganisms in the aftermath (Barton, P. 2016. Revealing the dynamics of a large impact. Science, v. 354, p. 836-837). That is, was the surrounding ocean sterilised at the time of the K-T (K-Pg) mass extinction?; an issue whose resolution is awaited with bated breath by the palaeobiology audience. OK; so theory about the physical process of cratering has been validated to some extent, but will later results be more interesting, outside the planetary sciences community?

Read more about impacts here and mass extinctions here .

Signs of life in some of the oldest rocks

Vic McGregor (left) and Allen Nutman examine metasedimentary strata at Isua, West Greenland
For decades the record of tangible signs of life extended back to around 3.4 billion years ago, in the form of undulose, banded biofilms of calcite known as stromatolites preserved at North Pole in the Pilbara region of Western Australia. There have been attempts to use carbon-isotope data and those of other elements from older, unfossiliferous rocks to seek chemical signs of living processes that extracted carbon from the early seas. Repeatedly, claims have been made for such signatures being extracted from the 3.7 to 3.8 Ga Isua metasediments in West Greenland. But because this famous locality shows evidence of repeated metamorphism abiogenic formation of the chemical patterns cannot be ruled out. Isua has been literally crawled over since Vic McGregor of the Greenland Geological Survey became convinced in the 1960s that the metasediments could be the oldest rocks in the world, a view confirmed eventually by Stephen Moorbath and Noel Gale of Oxford University using Rb-Sr isotopic dating. There are slightly older rocks in Canada, which just break the 4 Ga barrier, but they were metamorphose at higher pressures and temperatures and are highly deformed. The Isua suprcrustals, despite deformation and metamorphism show far more diversity that geochemically can be linked to many kinds of sedimentary and volcanic rock types.

 

Two of the Isua addicts are Allen Nutman of the University of Wollongong, Australia and Clark Friend formerly of Oxford Brookes University, UK, who have worked together on many aspects of the Isua rocks for decades. Finally, thanks to melt-back of old snow pack, they and colleagues have found stromatolites that push the origin of life as far back as it seems possible for geoscientists to reach (Nutman, A.P. et al. 2016. Rapid emergence of life shown by discovery of 3,700-million-year-old microbial structures. Nature, v. 537, published online 31 August 2016, doi:10.1038/nature). The trace fossils occur in a marble, formerly a limestone that retains intricate sedimentary structures, which show it to have been deposited in shallow water. The carbon and oxygen isotopes have probably been disturbed by metamorphism, and no signs of cell material remain for the same reason, but the shape is sufficiently distinct from those produced by purely sedimentary processes to suspect that they resulted from biofilm build-up. The fact that they are made of carbonates suggests that they may have been produced by cyanobacteria as modern stromatolites are.

isua strom

Stromatolite-like structures from a metasediment in the Isua area of West Greenland (credit Allen Nutman, University of Wollongong, Australia)

The age of the structures, about 3.7 Ga, is close to the end of the Late Heavy Bombardment (4. 1to 3.8 Ga) of the Solar System by errant asteroids and comets. So, if the physical evidence is what it seems to be, life emerged either very quickly after such an energetic episode or conditions at the end of the Hadean were not inimical to living processes or the prebiotic chemistry that led to them.

 You can find more on early life here

Allwood, A.C. 2016. Evidence of life in Earth’s oldest rocks. Nature, v. 537, published online 31 August 2016, doi:10.1038/nature19429

Hunting down the Tully Monster

The word ‘monster’ has its origin in the Latin monere ‘to warn’ but has broadened out in its usage.  It has even reverted to its origins as a verb: a highly critical, verbal attack. But I prefer ‘something about which one needs to be warned’, and the Tully Monster encapsulates that meaning. It once lived in Illinois, specifically at just a single location, Mazon Creek, where thousands of them have been seen. But should you be especially fearful of Tullimonstrum gregarium? Well, at first sight, no; it’s only about 10 cm long and apparently has no proper bones and it’s dead. The first was spotted in a coal-mine waste heap by Francis Tully in 1958, a pipefitter with an interest in Carboniferous fossils. Two years after his death in 1987, he and his monster were honoured by a bill that the Illinois State Legislature passed to make it the official State Fossil.

Artist's impression of the Carboniferous Tully Monster (

Artist’s impression of the Carboniferous Tully Monster (Tullimonstrum gregarium) (credit: Sean McMahon, Yale University)

It seems to have become a ‘monster’ by stumping all previous attempts to categorise it; so much so that it long served as a warning to eager palaeontologists not to tangle with its taxonomy. That’s not surprising, because as well as bearing a passing resemblance to Captain Nemo’s submarine in Jules Verne’s 20 000 leagues Under the Sea, it has some truly astonishing features.  Portholes down its sides are not the weirdest – actually they are gill openings. It has a biting apparatus at the end of an absurdly lengthy forward protuberance, that would not be unexpected if it were one of those fish from the Amazon that, you know, men really ought to be warned about. Most of us would not share a bath with it if we had been. And then, there are the eyes on the ends of a dorsal bar which would give Tullimonstrum gregarium superb stereoscopic vision to guide it unerringly to its target, lashing its efficient-looking caudal fin. The fact that it has only a single nostril is merely puzzling by comparison.

Six decades on, Victoria McCoy of Yale University (now at Leicester University, UK) and 15 undeterred colleagues have pored over more than 1200 Tully Monster fossils and seem to have cracked its affinities (McCoy, V.E. et al. 2016. The ‘Tully monster’ is a vertebrate. Nature, v. 532, p. 496-499). In fact, it’s surprising that it has remained an enigma for so long, because McCoy and colleagues have documented almost every aspect of its anatomy, available from a huge number of superbly preserved specimens – teeth, fin, muscle traces, gills, nostril, notochord, gut and so on. As well as being a vertebrate, its dreadful proboscis is very like that of the Cambrian oddity Opabinia from the Burgess Shale. A  separate study by four British palaeontologists and a Texan concentrated on the eyes using electron microscopy and found ‘ultrastructural details’, including pigment cells (Clements, T. et al. 2016. The eyes of Tullimonstrum reveal a vertebrate affinity. Nature, v. 532, p. 500-503) which unequivocally confirm that it is a vertebrate. It has all the hallmarks of being related to lampreys and hagfishs. They devour rotting, drowned corpses.

Further pounding for ideas on the Ediacaran fauna

About 635 Ma ago fossils of large-bodied organisms first appeared in the geological record: some quilt like, others with a crude bilateral symmetry, more looking like ‘mud-filled bags’ and ribbed discs but none that can easily be distinguished as animals, plants or colonial microorganisms. First found abundantly in the Ediacara Hills of South Australia, hence their sack-name the Ediacaran biota, it now seems that they were distributed globally in the late Neoproterozoic Era. Interpreting their metabolism is risky enough – some are reckoned to be animals that absorbed nutrients through their skin, others said to be dependent on photosynthesis – but a controversy has raged for many years over the kind of environment in which they thrived. In a detailed 2012 study of sedimentary structures petrography in the South Australian sandstones from which they were first described, Gregory Retallack of the University of Oregon inferred that some lived on land and are now found in palaeosols: they include Spriggina, Dickinsonia and Charnia that are among the most favoured candidates for being animals or some kind. Others inhabited shallow water. Anticipating fiery disputes a Nature editorial appeared in same issue in which Retallack published his paper .

Rich fossil assemblage of the Ediacaran Mistaken Point Formation, Newfoundland. (Credit: Alex Liu, Earth Sciences, University of Bristol)

Rich fossil assemblage of the Ediacaran Mistaken Point Formation, Newfoundland. (Credit: Alex Liu, Earth Sciences, University of Bristol)

Retallack has now moved on to the even more fossil-rich Ediacaran sediments of Newfoundland (Retallack, G.J 2016. Ediacaran sedimentology and paleoecology of Newfoundland reconsidered. Sedimentary Geology, v. 333, p. 15-31). Eye-wateringly detailed sequence stratigraphy of the now famous Mistaken Point locality and others suggests that the ecosystem there was an intertidal salt marsh. In detail it contains evidence for shallow-water graded bedding, signs of regular storms and perhaps tsunamis together with interbedded palaeosols and subaerial volcanic crystal tuffs whose feldspars survive intact. The palaeosols can be subdivided into several pedogenic types akin to those used to classify modern soils. Unlike the arid setting of the South Australian Ediacaran sediments, whose palaeosols show signs of freezing, the Newfoundland package indicates humid, cool-temperature climes

As in Australia, the palaeosols are rich in Ediacaran fossils, including the best known; the leaf-like Charnia and its discoidal support structure that appears in Retallack’s reconstruction of the environment in an analogous way to salt-tolerant shrubs in modern tidal flats. They occur together with encrusting fossils that bear some resemblance to modern foliose fungi or lichens. Further chuntering in the palaeontological community seems inevitable, but the sedimentological observations alone knock one hypothesis on the head: it has been said that the graded bedding common to both major Ediacaran assemblages constitutes evidence for deep marine origins from turbidity currents. But there is further compost in which controversy may thrive, in that Retallack ascribes the repeated palaeosols to glacially controlled sea-level fluctuations: the Newfoundland sequence contains two diamictites interpreted as tillite, one dated at ~583 Ma the other undated but at the top of the sequence.

More on early life

A rational view of the start of human influences on Life and Geology

Regular readers will know that I have strong views on attempts to burden stratigraphy with a new Epoch: the Anthropocene. The central one is that the lead-in to a putsch has as much to do with the creation of a bandwagon, to whose wheels all future geologists will be shackled, as it does to any scientific need for such a novelty. Bound up as it is with the fear that Earth may be experiencing its sixth mass extinction, the mooted Anthropocene will likely become a mere boundary marked by future stratigraphers as a Global Boundary Stratotype Section and Point or GSSP between the existing Holocene Epoch and that sequence of sedimentary strata and their fossil record that will be laid down on top of it. Or not, if humanity becomes extinct should the economically induced, dangerous modifications of our homeworld of the last few decades or centuries not be halted. Either way, it defies the stratigraphic ‘rule book’.

No one can deny that humanity’s activities are now immensely disruptive to surface geological processes. Nor is it possible to rule out such disruptive change to the biosphere in the near-future that a latter-day equivalent of the K/Pg or end-Permian events is on the cards: such confidence does not spring from the interminable succession of grand words and global inaction reiterated in December 2015 by the UN Paris Agreement on economically-induced climate change. Still, it was a bit of a relief to find that palaeontological evidence, or rather statistics derived from the fossil record in North American sedimentary rocks since the Carboniferous, emphasises that there is no need for the adoption of Anthropocene as an acceptable geological adjective.

To ecologists, extinctions are not the be all and end all of disruption of the biosphere. Major shifts in life’s richness are also recorded by the way entire ecosystems become disrupted. A classic, if small-scale, example is that way in which the ecosystem of the US Yellowstone National Park changed since the eradication by 1926 of the few hundred grey wolves that formerly preyed mainly on elk. In the 20 years since wolf reintroduction to the Park in 1995 the hugely complex but fragile Yellowstone ecosystem has showed clear signs of recovery of its pre-extirpation structure and diversity.

A consortium of mainly US ecologists, led by Kathleen Lyons of the National Museum of Natural History at the Smithsonian Institution in Washington DC, has assessed linkages between species of fossil animal and plants since the Carboniferous (S.K. Lyons and 28 others, 2015. Holocene shifts in the assembly of plant and animal communities implicate human impacts. Nature, published on-line 16 December 2015 doi:10.1038/nature16447). They found that of the 350 thousand pairs of species that occurred together at different times throughout the late Palaeozoic to the last Epoch of the Cenozoic, the Holocene, some pairs appeared or clustered together more often than might be expected from random chance. Such non-random association suggests to ecologists that the two members of such a pair somehow shared ecological resources persistently, hinting at relationships that helped stabilise their shared ecosystem. For most of post-300 Ma time an average of 64% of non-random pairs prevailed, but after 11.7 ka ago – the start of the Holocene – that dropped to 37%, suggesting a general destabilisation of many of the ecosystems being considered. This closely correlates with the first human colonisation of the Americas, the last of the habitable continents to which humans migrated. This matches the empirical evidence of early Holocene extinctions of large mammals in the Americas, which itself is analogous to the decimation of large fauna in Australasia during the late Pleistocene following human arrival from about 50 to 60 ka ago. Significant human-induced ecological impact seems to have accompanied their initial appearance everywhere. The ecological effects of animal domestication and agriculture in Eurasia and the Americas mark the Holocene particularly. In fact, in Europe the presence of Mesolithic hunter gatherers is generally inferred, in the face of very rare finds of artefacts and dwellings, from changes in pollen records from Holocene lake and wetland sediments, which show periods of tree clearance that can not be accounted for by climate change.

There is no need for Anthropocene, other than as a political device.