Earth-logs

Human penis bone lost through monogamy?

Published on December 23, 2016 by zooks777Leave a comment

The baculum or penis bone is arguably the most variable of mammalian bones, present in some species but not others. Among those in which it does occur the baculum varies enormously in shape, length and breadth relative to body size. This makes it likely to have been subject to the most divergent evolution among mammals. Yet its evolution has remained somewhat puzzling until recently. Observation has shown that the width of the baculum in male house mice is positively correlated with reproductive success. So one factor in the bone’s evolution may be postcopulatory sexual selection: female mice seem to favour males well endowed in this department once they have mated with them, a notion supported by careful laboratory experimentation. The physical role of the penis bone is to support and protect the penis during sexual intercourse. Sturdy dimensions are increasingly efficacious the longer the duration and the greater the frequency of copulation, particularly among polygamous and seasonally breeding species. They also tend to delay or inhibit a female mating with another male after copulation.

Walrus baculum, approximately 22 inches long — Walrus baculum, approximately 0.6 metres long (credit: Wikipedia)

Matilda Brindle and Christopher Opie of University College London have applied advanced phylogenetic statistical analysis to data on the dimensions of penis bones among 2000 mammal species (Brindle, M. & Opie, C. 2016. Postcopulatory sexual selection influences baculum evolution in primates and carnivores. Proceedings of the Royal Society, B, v. 283, doi: 10.1098/rspb.2016.1736) and suggest that the baculum first evolved in mammals between 145 to 95 Ma ago, earlier mammals likely having no penis bone. Ancestral primates and carnivorous mammals, however, were so endowed. Yet some mammalian species have lost the baculum. Among the primates human males do not have one whereas male chimpanzees and bonobos, with which we share a last common ancestor, do: both are boisterously promiscuous whereas humans are pair-bonded to a large degree.

The issue of polygamy versus monogamy among human ancestors, and when the latter emerged, continues to exercise palaeoanthropologists. The former in other living primates is often associated with a marked contrast in size between males and females – sexual dimorphism. The earliest hominins, such as species of Australopithecus, did exhibit such dimorphism whereas species of Homo show significantly less size contrast, which some have taken to mark the emergence of pair-bonding amongst members of the earliest human species to be passed on to their successors. Another indicator of competitiveness among primate males for females, and their dominance over the latter, is the near universal possession of large canine teeth among males of polygamous primates; an odd feature for species whose diet is dominantly and often exclusively vegetarian. Not only do living humans not have prominent canines, neither do any known fossil hominins. Despite the views of a small minority of anthropologists who demand that modern human females won social parity with males only in the last 100 thousand years, only to lose it following the Neolithic ‘revolution’, the physical evidence suggests that a trend towards that emerged with other distinct characteristics of hominins and concretised in early Homo. An assiduous search for fossil hominin penis bones may yet reveal the moment of monogamy.

Mankind lost its penis bone as we evolved and monogamy may be to blame – or thank

Geoscience academic under threat

Published on December 19, 2016 by zooks777Leave a comment

While she was US Secretary of State from 2009 to 2013, Hilary Clinton the 2016 Democrat candidate for presidential office habitually used her private email server to send and receive messages, both personal and concerning affairs of state. She did not activate a state.gov email account for the official stuff, saying that it was ‘for convenience’ as her Blackberry smartphone could only access on account. More than 30 thousand undeleted e-mails were hacked by ‘persons unknown’ and appeared on Wikileaks in early 2016, with more in late October 2016, to become one of several issues central to the 2016 US presidential campaign. This practice was twice exonerated by the FBI, despite her account proving to be insecure and the risk to state secrets.

Hans Thybo, President of the European Geophysical Union and a widely esteemed professor of seismology at the University of Copenhagen, was not so lucky. He was fired by the University authorities, allegedly for using his private email account for work-related issues and advising a postdoctoral fellow that criticising the University’s management was ‘legitimate’. More than 1000 academic colleagues have petitioned the University of Copenhagen to reverse its decision and reinstate Thybo, and his case was central to the lead editorial A creeping corporate culture in Nature of 15 December 2016.

Anyone connected for more than a few years with academic life in probably every university on the planet will be conscious of the spread of a culture of bureaucratic control, corporatism and commodification in what formerly were largely self-governing institutions of higher education and research. The trend is in line with increasing, omnidirectional economic pressures stemming from the aftermath of the 2007-8 global financial crisis. But it is not entirely new. My own experience suggests it is partly a logical outcome of leading academics becoming increasingly prone to saying ‘Yes’; at best simply disengaging from dispute with a growing managerial caste within education and research, at worst by opportunistically joining it. A serious disjuncture has developed between teachers and researchers and the managers and business administrators in institutions of higher education. Symptomatic of this kind of schism was the recent passing of a motion of no confidence in the Vice Chancellors Executive of Britain’s Open University by its unionised academic and academic-related staff, following disastrous bungling of a new means of tuition of its entirely non-residential undergraduates in the current academic year. Those who were to implement the measures were inadequately consulted by the leading managers, most of whom had little experience of how the OU had functioned successfully since it received its Charter in 1969.

In Britain, checks and balances on the requirements of management and faculty historically centred on their Senate, once the primary academic authority of universities, in which all members of both academic and non-academic sectors freely debated and passed judgement on new directions and the abandonment of practices that had been found wanting. In most institutions, the Senate has been reduced since the mid 1980s to a mere fraction of staff, who, after nomination, are elected by the various components of the institution, together with unelected, ex officio, members of senior management. In practice, Senates now generally act as a ‘rubber stamp’ for decisions of the top echelons, much in the manner of business corporations.

Part of the new culture attempts to regulate electronic communications. An example of such an IT regulation states that the institution ‘… may monitor all data, systems and network traffic at any time …’, i.e. it claims ownership of work-related communication. No wonder Hans Thybo fell foul of his university. Should outside pressure persuade the authorities of the University of Copenhagen to reinstate him, that would be a significant blow against what has become an unwholesome aspect of learning and scholarship.

Sacking of prominent geoscientist rocks community

‘Big data’ on water resources

Published on December 18, 2016 by zooks777Leave a comment

Two petabytes (2×10¹⁵) is a colossal number which happens to approximate how much data has been collected in geocoded form by the Landsat Thematic Mapper and its successors since it was first launched in 1984. In tangible form these would occupy about half a million DVDs, weighing in at about 8 metric tonnes; ‘daunting’ comes nowhere near describing the effort needed to visually interpret this unique set of multi-date imagery. Using the Google Earth Engine, the free cloud-computing platform for big sets of image data which hosts all Landsat data and much else (but not yet the equally daunting ASTER data – roughly a million 136 Mb scenes) the 32 years-worth has been analysed for its content of hydrological information by the European Commission’s Joint Research Centre in Italy, with assistance from Google Switzerland. Using the various spectral characteristics of water in the visible and infrared region, the team has been able to assess the position on the continents of surface water bodies larger than 900 m², both permanent and ephemeral, and how the various categories have changed in the last 32 years (Pekel, J.-F. et al. 2016. High-resolution mapping of global surface water and its long-term changes. Nature, v. 540, p. 418-422; doi:10.1038/nature20584). The results are conveniently and freely available in their entirety at the Global Surface Water Explorer, an unparalleled and easy-to-use opportunity for water resource managers, wetland ecologists and geographers in general.

Among the revelations are sites and areas that have been subject to gains and losses in water availability, the extents of new and vanished permanent and seasonal water bodies and the conversion of one to the other. A global summary gives a net disappearance of 90 thousand km² of permanent water bodies, about the area of Lake Superior, but exceeded by new permanent bodies totalling 184 thousand km². There has been a net increase in permanent water on all continents except Oceania with a loss one percent (note that Antarctica and land north of the Arctic Circle were not analysed). More than 70 % of the losses are in the semi-arid Middle East and Central Asia (Iran, Iraq, Uzbekistan, Kazakhstan and Afghanistan), due mainly to overuse of irrigation, dam construction and long-term drought. Much of the increase in water occurrence stems from reservoir construction, but climate change may have played a part through increased precipitation and melting of high-altitude snow and ice, as in Tibet.

The Aral Sea in Uzbekistan and Kazakhstan has suffered dramatic loss of standing and seasonal water cover due to overuse of water for irrigation from the two main rivers, the Amu (Oxus) and Syr, that flow into it. Note the key to the colours that represent different categories of changes in surface water. (Credit: Global Surface Water Explorer)

Many of the lakes in the northern Tibetan Plateau have grown in size during the last 32 years, mainly due to increased precipitation and snow melt. (Credit: Global Surface Water Explorer)

There are limitation to the accuracy of the various categories of change, one being the persistence of cloud cover in humid climates, another being the sometimes haphazard scheduling of Landsat Data capture (in some case that has depended on US Government interest in different areas of the world).

More detail on using remote sensing in exploration for and evaluation of water resources can be found here.

When did the Greenland ice cap last melt?

Published on December 12, 2016 by zooks777Leave a comment

The record preserved in cores through the thickest part of the Greenland ice cap goes back only to a little more than 120 thousand years ago, unlike in Antarctica where data are available for 800 ka and potentially further back still. One possible reason for this difference is that a great deal more snow falls on Greenland so the ice builds up more quickly than in Antarctica. Because ice flows under pressure this might imply that older ice on Greenland long flowed to the margins and either melted or calved off as icebergs. So, although it is certain that the Antarctic ice cap has not melted away, at least in the last million years or so, we cannot tell if Greenlandic glaciers did so over the same period of time. Knowing whether or not Greenland might have shed its carapace of ice is important, because if ever does in future the meltwater will add about 7 metres to global sea level: a nightmare scenario for coastal cities, low-lying islands and insurance companies.

Margin of the Greenland ice sheet (view from p... — Edge of the Greenland ice sheet with a large glacier flowing into a fjiord at the East Greenland coas (Photo credit: Wikipedia)

One means of judging when Greenland was last free of ice, or at least substantially so, is based on more than a ice few metres thick being opaque to cosmic ‘rays’. Minerals, such as quartz, in rocks bared at the surface to ultra-high energy, cosmogenic neutrons accumulate short-lived isotopes of beryllium and aluminium – ¹⁰Be and ²⁶Al with half-lives of 1.4 and 0.7 Ma. Once rocks are buried beneath ice or sediment, the two isotopes decay away and it is possible to estimate the duration of burial from the proportions of the remaining isotopes. After about 5 Ma the cosmogenic isotopes will have decreased to amounts that cannot be measured. Conversely, if the ice had melted away at any time in the past 5 Ma and then returned it should be possible to estimate the timing and duration of exposure of the surface to cosmic ‘rays’. Two groups of researchers have applied cosmogenic-isotope analysis to Greenland. One group (Schaefer, J.G. et al. 2016. Greenland was nearly ice-free for extended periods during the Pleistocene. Nature, v. 540, p. 252-255) focused on bedrock, currently buried beneath 3 km of ice, that drilling for the ice core finally penetrated. The other systematically analysed the cosmogenic isotope content of mineral grains at different depths in North Atlantic seafloor sediment cores, largely supplied from East Greenland since 7.5 Ma ago (Bierman, P.R. et al. 2016. A persistent and dynamic East Greenland Ice Sheet over the past 7.5 million years Nature, v. 540, p. 256-260). As their titles suggest, the two studies had conflicting results.

The glacigenic sediment grains contained no more than 1 atom of ¹⁰Be per gram compared with the 5000 to 6000 in grains deposited and exposed to cosmic rays along the shores of Greenland since the end of the last ice age. These results challenge the possibility of any significant deglaciation and exposure of bedrock in the source of seafloor sediment since the Pliocene. The bedrock from the base of Greenland’s existing ice cap, however, contains up to 25 times more cosmogenic isotopes. The conclusion in that case is that there must have been a protracted, >280 ka, exposure of the rock surface in what is now the deepest ice cover at 1.1 Ma ago at most. Allowing for the likelihood of some persistent glacial cover in what would have been mountainous areas in an otherwise substantially deglaciated Greenland, the results are consistent with about 90% melting suggested by glaciological modelling.

Clearly, some head scratching is going to be needed to reconcile the two approaches. Ironically, the ocean-floor cores were cut directly offshore of the most likely places where patches of residual ice cap may have remained. Glaciers there would have transported rock debris that had remained masked from cosmic rays until shortly before calved icebergs or the glacial fronts melted and supplied sediment to the North Atlantic floor. If indeed the bulk of Greenland became ice free around a million years ago, under purely natural climatic fluctuations, the 2° C estimate for global warming by 2100 could well result in a 75% glacial melt and about 5-6 m rise in global sea level.

Read more about glaciation here and here.

Tree-climbing australopithecines

Published on December 9, 2016 by zooks7771 Comment

We know that Lucy, the famous Australopithecus afarensis, could climb trees because her many bone fractures show that she fell out of a tree to her death. But that does not mean her species was an habitual tree-climber: plenty of modern humans fall to their deaths from trees, cliffs and the like. But the issue seems to have been resolved by using X-ray tomography of Lucy’s limb bones (Ruff, C.B. et al. 2016. Limb bone structural proportions and locomotor behaviour in A.L. 288-1 (“Lucy”). PLOS ONE v. 11, e0166095. doi:10.1371/journal.pone.0166095) during the skeleton’s triumphal series of exhibits in the US.



Embed from Getty Images

The authors, including two of those who showed that Lucy died after a fall using similar data, compared the digital 3-D models of her surviving arm- and leg bones with those of other hominins and living primates, estimating their relative strengths at different positions. Lucy was probably stronger in the arm than in the leg, but not to the same degree as chimpanzees. This is a feature that would significantlyassist climbing , but her bipedal locomotion on the ground would have been only slightly different from that of later Homo species. If anything, her strength relative to size would have been greater than ours, perhaps reflecting less reliance on tools for getting food and defending herself. But almost certainly Australopithecus afarensis habitually spend more time in trees, perhaps foraging and as a defence against predation, especially at night.

The new data for Lucy allows palaeoanthropologists to better judge the capabilities of other hominins. Interestingly Homo habilis, the earliest of our genus, may have had similar habits. But later species, beginning with H. erectus/ergaster, were as Earth-bound as we are. This suggests a shift in hominin ecology from an early and probably long history of semi-arboreal behavior until humans became masters of their terrain about 1.9 Ma ago, probably through their invention of better tools and the controlled use of fire.

Read more about human evolution here and here

A challenge to the concept of species

Published on November 25, 2016 by zooks777Leave a comment

Comparison of DNA from ancient hominin fossils with that obtained from a broad spectrum of living people showed that on the road out of Africa in the last 130 thousand years some anatomically modern humans successfully interbred with Neanderthals and Denisovans to produce fertile offspring. All non-African people contain a trace of those liaisons and include fertile hybrids in their ancestry, whereas Africans do not. Using quick, low-cost and sensitive genomic analyses these discoveries made similar searches for hybridisation among other supposedly distinct species a popular and fruitful line of research (Pennisi, E. 2016. Shaking up the tree of life. Science, v. 354, p. 817-820; doi: 10.1126/science.354.6314.817). They also challenge the long-held view that individual species are incapable of fertile interbreeding with others. Yet fertile hybrids have long been known among plants and butterflies without recourse to genomics. Now that it is a basic tool, it has been shown that up to 10% of known plant species have arisen from hybrids and examples are quickly being found among birds, insects, fish and mammals, including the famous Galapagos finches. Hybridisation introduces genetic variation more quickly than does mutation, potentially a major advantage in adaptive radiation.

Page from Darwin's notebooks around July 1837 ... — Page from Darwin’s notebooks around July 1837 showing his first sketch of an evolutionary tree. (credit: Wikipedia)

Of course, the concept of ‘species’ is arbitrarily based on biological ‘form and function’, and in the same fashion as discoveries about epigenetics have shown genetic determinism to have an air of dogma, so hybridisation suggests that a ‘web’ is more apt as shorthand for the progress of evolution than is Darwin’s ‘tree’ or even a tangled ‘bush’. Another welcome outcome spurred by the pioneers of hominin comparative genetics is a powerful challenge to the dominant philosophies of reductionism and dualism among scientists; legacies of René Descartes bound up with the ‘scientific method’ – especially among physical scientists – and ideas such as ‘nature versus nurture’. A major revolution is in progress, from which the seekers for a Theory of Everything, from quantum mechanists through particle physicists to cosmologists need to draw some sharp and perhaps embarrassing lessons.

It is appropriate that the driving agency lies within anthropology, and thrilling too, for everyone can quickly learn a new way of approaching the world by contemplating their own origins. They would be hard-pressed to do that by pondering on the early nanoseconds of the cosmos …

DNA From Mystery Human Species Detected in Pacific Islanders

K-T (K-Pg) boundary impact probed

Published on November 24, 2016 by zooks777Leave a comment

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).

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 .

Lunar gravity and the Orientale Basin

Published on November 6, 2016 by zooks777Leave a comment

Mapping the Earth’s gravitational field once involved painstaking use of highly sensitive gravimeters at points on the surface, then interpolating values in the spaces between. How revealing maps produced in this way are depends on the spacing of the field sites, and that is still highly variable because of accessibility and how much money is available to carry out such a task in different areas. Space-borne methods have been around for decades. One uses radar measurement of sea-surface height, which depends on the underlying gravitational field. The other deploys two satellites in tandem orbits (the US-German Aerospace Centre Gravity Recovery and Climate Experiment – GRACE), the distance between them – measureable using radar – varying along each orbit according to variations in the Earth’s gravity. Respectively, these methods have produced gravity maps of the ocean floor and estimates melting rates of ice caps and the amount of groundwater extraction from sedimentary basins. The problem with GRACE is that satellites need to avoid the Earth’s atmosphere by using orbits hundreds of kilometres above the surface, otherwise drag soon brings them down. So the resolution of the gravity maps that it produces is too coarse (about 270 km) for most useful applications. If a world has no atmosphere, however, there is no such limit on orbital altitude, other than surface topography. A similar tandem-system to GRACE has been orbiting the Moon at 55 km since 2011. The Gravity Recovery and Interior Laboratory (GRAIL) mission has produced full coverage of lunar gravity at a resolution of 20 km. In a later phase of operation, GRAIL has been skimming the tops of the highest mountains on the Moon at an average altitude of 6 km; close enough to give a resolution of between 3 and 5 km.

This capacity has given a completely new take on lunar near-surface structure, about as good as that provided by conventional gravity mapping for parts of the Earth. The first pay-off has been for the best preserved major impact feature on the lunar surface: the Orientale basin that formed at the end of the Late Heavy Bombardment of the Solar System, around 3.8 billion years ago. The ~400 km diameter Orientale basin is at the western border of the moon’s disk visible from Earth, and looks like a gigantic bullseye. Its central crater, floored by dark-coloured basalt melted from the mantle by the power of the impact, is surrounded by three concentric rings extending to 900 km across; a feature seen partially preserved around even larger lunar maria. The structure of such giant ringed basins – also seen on other bodies in the Solar System – has been something of a puzzle since their first recognition on the Moon. A popular view has been that they are akin to the rippling produced dropping a pebble in water, albeit preserved in now solid rock.

The Orientale basin superimposed by the strength of the moon's gravity field. Areas shaded in red have higher gravity, while areas in blue have the least gravity. (Credit: Ernest Wright, NASA/GSFC Scientific Visualization Studio) — The Orientale basin superimposed by the strength of the moon’s gravity field. Areas shaded in red have higher gravity, while areas in blue have the least gravity. (Credit: Ernest Wright, NASA/GSFC Scientific Visualization Studio)

GRAIL has allowed planetary scientists to model a detailed cross section through the lunar crust (Zuber, M.T. and 27 others, 2016. Gravity field of the Orientale basin from the Gravity Recovery and Interior Laboratory Mission. Science, v. 354, p. 438-441). The 40 km thick anorthositic (feldspar-rich) lunar crust has vanished from beneath the central crater, which is above a great upwards bulge of the lunar mantle mantled by about 2 km of mare basalts. The shape of the crust-mantle boundary beneath the rings shows that it has been thickened by anorthositic debris flung out by the impact. But the rings seem to be controlled by huge faults that penetrate to the mantle: signs of 2-stage gravitational collapse of the edifice produced initially by the impact.

Palaeontologists with beards: some shocking news

Published on October 21, 2016 by zooks777Leave a comment

Mary Anning, now something of a feminist icon, combed the foreshores and undercliffs of the Jurassic Coast of southern England for fossils, including those of marine reptiles. Self-taught, she unearthed, prepared and described the first ichthyosaurs and plesiosaurs known to science. Being a working class woman – and she did work in the early 19^th century – she was not allowed to publish. Instead, she provided fossils to notables like Owen, Buckland and Cuvier who published and got the credit, only rarely acknowledging her as the collector. In 1964, during my induction as a fresher in the Lapworth Library of the Geology Department at Birmingham University, the ‘Prof’ Fred Shotton declared to the 14 young men sitting meekly before him, ‘There will be no women students in this department while I am its Head’. By my final year, Fred had relented and the first ever female undergraduate enrolled. When I left with a PhD in 1970, there were more and now my guess is the proportion is around 40%.. But professional geoscience is still largely a man’s world. In the US, where geoscience is still a major science – it has declined in Britain as a result of ‘rationalisation’ of UK Earth science departments that followed the 1987 Oxburgh Report – a mere 16% of faculty are women; female PhDs are paid 12% less than males; fellowship of learned societies is below 20%, and there is a host of other issues in which women are ‘less favoured’. It’s much the same, although perhaps a little less blatant, in most sciences. Being in a discipline that is still largely focussed on field work by individuals, female ‘lone workers’ in often remote places sometimes face worse problems.

Three of the presenters in the Bearded Lady project pose on the foreshore at Lyme Regis - note Golden Cap in the background. (Credit: Kelsey Vance) — Three of the presenters in The Bearded Lady Project pose on the foreshore at Lyme Regis – note the weathered Cretaceous Upper Greensand forming Golden Cap in the background. (Credit: Kelsey Vance)

Asking themselves a few rhetorical questions, such as, ‘What comes to mind when you hear the word “palaeontologist”?’ or ‘List as many female scientists as you can’, three women professionals – a palaeontologist, a performance art director and a photographer – decided to challenge a few stereotypes. Their project is a feature length, live-action documentary plus a series of photographic exhibitions to inspire young women to become geoscientists. It centres on what most ‘geos’ really enjoy; field work conducted exclusively by women. It is as realistic as the common perception of field geology might suggest, yet at some point each of the presenters has a beard or moustache. Hence, The Bearded Lady Project! Part of the film is to include footage shot at Lyme Regis, as a tribute to Mary Anning, the whole project covering many different aspects of practical geoscience.

For British readers: The Bearded Lady Project’s portrait exhibition is planned to be in Exeter.

See also: Witze, A. 2016. Q&A: Lexi Jamieson Marsh and Ellen Currano: Face to face. Nature v. 538, p. 316.

Impact linked to the Palaeocene-Eocene boundary event

Published on October 20, 2016 by zooks777Leave a comment

The Palaeocene–Eocene (P-E) boundary at 55.8 Ma marks the most dramatic biological changes since the mass extinction at the Cretaceous-Palaeogene boundary 10 million years earlier. They included the rapid expansions of mammals and land plants and major extinction of deep-water foraminifera. It was a time of sudden global warming (5-10°C in 10-20 ka) superimposed on the general Cenozoic cooling from the ‘hothouse’ of the Cretaceous Period. It coincided with a decrease in the proportion of ¹³C in marine carbonates. Because photosynthesis, the source of organic carbon, favours light ¹²C, such a negative δ¹³C “spike” is generally ascribed to an unusually high release of organic carbon to the atmosphere. The end-Palaeocene warming may have resulted from a massive release of methane from gas-hydrate buried in shallow seafloor sediments. But another process may yield such a signature; massive burning of organic material at the land surface. Since its discovery, the P-E thermal maximum has been likened to the situation that we may face should CO₂ emissions from fossil-fuel burning continue to rise without control. Unsurprisingly, funds are more easily available for research on this topic than, say, ‘Snowball Earth’ events.

Climate change during the last 65 million year... — Climate change during the last 65 million years. The Paleocene–Eocene Thermal Maximum is labelled PETM. (Photo credit: Wikipedia)

Three seafloor sediment cores off the east coast of the US that include the P-E boundary have been found to contain evidence for an impact that occurred at the time of the δ¹³C “spike” (Schaller, M.F. et al. 2016. Impact ejecta at the Paleocene-Eocene boundary. Science, v. 354, p. 225-229). The evidence is dominated by tiny spherules and tear-shaped blobs of glass, some of which contain tiny crystals of shocked and high-temperature forms of silica (SiO₂). These form part of the suite of features that have been used to prove the influence of asteroid impacts. Two other onshore sites have yielded iridium anomalies at the boundary, so it does look like there was an impact at the time. The question is, was it large enough either to cause vast amounts of methane to blurt out from shall-water gas hydrates or set the biosphere in fire? Two craters whose age approximates that of the P-E boundary are known, one in Texas the other in Jordan, with diameters of 12 and 5 km respectively; far too small to have had any global effect. So either a suitably substantial crater of the right age is hidden somewhere by younger sediments or the association is coincidental – the impact that created the Texan crater could conceivably have flung glassy ejecta to the area of the three seafloor drilling sites.

Almost coinciding with the spherule-based paper’s publication another stole its potential thunder. Researchers at Southampton University used a mathematical model to investigate how a methane release event might have unfolded (Minshull, T.A. et al. 2016. Mechanistic insights into a hydrate contribution to the Paleocene-Eocene carbon cycle perturbation from coupled thermohydraulic simulations. Geophysical Research Letters, v. 43, p. 8637-8644, DOI: 10.1002/2016GL069676). Their findings challenge the hypothesized role of methane hydrates in causing the sudden warming at the P-E boundary. But that leaves out the biosphere burning, which probably would have neded a truly spectacular impact.

More on mechanisms for ancient climate change

Can melting of frozen methane explain rapid climate change 56 million years ago?

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