Former Senior Lecturer at British Open University, research in remote sensing of arid lands, groundwater exploration, Precambrian tectonics and geochemistry
Of the fossil fuels coal has long been assumed to be the most plentiful, even the most pessimistic forecasters having acknowledged a global lifetime of centuries for known reserves. The determination of the emerging giant economies of China and India and of the USA to fuel themselves through coal-burning seems inevitable if highly risky for the climate. But that depends on coal remaining the cheapest fuel, largely because of the sheer abundance of supplies. A recent commentary on coal (Heinberg, R. & Fridley, D. 2010. The end of cheap coal. Nature, v. 268, p. 367-369) suggests that there is a growing tendency for reserve estimates to decrease as geologists factor in practical restrictions – place, depth, seam thickness and quality – on feasibility under current mining conditions, instead of just looking at known masses of coal. Astonishingly, the end-19th century estimate of five thousand years of US coal supplies dropped to about 400 years by 1974 and is currently judged to be 240 years. China and India look likely to have less than 60 years-worth left. On top of that, the widely publicized turn to carbon capture and storage (CCS)for ‘clean-coal’ future supplies will inevitably drive-up prices of coal-fired energy. The two main factors in this remarkable transformation of ‘King Coal’ are fundamental economic forces in capitalism and the increasing refusal of miners to accept dangerous working conditions. The second is especially the case for China, where most coal is deep-mined; in the late 1990s it saw a drive to close down unsafe mines that caused production to fall, although it has greatly accelerated this century – further driving down coal’s lifetime there. It seems from this analysis that any realistic hope for a CCS-based coal economy, especially in China and India, depends on declining safety and environmental standards in their largely underground mines, which in turn depends on the highly unlikely willingness of their workforces to accept worse conditions.
Some scientists have enormous publication records, a notorious case being one who claimed personal discovery of the HIV virus. During the 1980s, this person managed to figure as an author in up to 90 papers a year, despite mainly travelling back and forth to conferences. If the same name appears again and again in publications – it makes little difference where it figures in the list of authors – it is that name that is remembered as an “authority”. In some cases such an accolade is deserved, in others it is engineered by a variety of devices: the same data can be used over and over (most blatantly if those data are ‘engineered in the first place); a place in an authors’ list can result from being a ‘guest’, in the manner of a faded star, ‘down on their luck’, who pops up with a one-line cameo in a film (I rule out Alfred Hithcock’s appearance as a bystander in every film that he made); by nicking the ideas and words of others; through the device of self plagiarism. The last is an especially cunning ploy, as it also saves time crafting text. The italicized sentence above is an example self-plagiarised from the March 2002 issue of EPN (Credit where credit is due?), but as a blogger I can do that with a clear conscience; Earth Pages News is highly unlikely to get me into the ‘Professoriat’, especially my inability to resist occasional items such as this! Having provided the original source reference, I am safe from universal condemnation.
Potentially the game is up for plagiarists and pot-boilers in peer-reviewed journals through scanning software (e.g. Turnitin) that checks text against web-available journals. Self-plagiarism may well be an oxymoron, but it serves as CV fodder as well as creating academic redundancy. It hit the news (Reich, E.S. 2010. Self-plagiarism case prompts calls for agencies to tighten rules. Nature, v. 468, p. 745) because of a case in Canada where an author’s peer-reviewed portfolio was found to contain 20 instances. No academic censure ensued, but three of his papers were retracted. Using the Déjà Vu facility to check biomedical literature has resulted in 79 thousand cases of duplicated wording in abstracts and titles alone, and the eventual retraction of almost 100 articles. Seemingly, journal editors are allowing repeated use of text in the ‘methods’ sections of papers, so a geochemist minor co-author, who gets a ride for a small contribution based on use of a particular piece of equipment might be safe in that regard, there being safety in numbers. Yet as the use of anti-plagiarism software spreads into the wider on-line literature its original targets, undergraduate and graduate students, may decide that the biter ought to be bit and turn the cyber searchlight on their ‘betters’…
Dunkleosteus (10 m long) of the Late Devonian. Image by Travis S. via Flickr
Probably the greatest ecological truism is that without oxygen there would be no life forms on Earth above the level of a restricted number of prokaryotes. Since around 2.4 Ga, when free atmospheric oxygen first appeared, levels have risen to the present 21% – it was probably as high as ~30% in the Carboniferous and Cretaceous Periods. Charting the rise has been difficult and the history of oxygen is written with a very broad brush. If there had been sudden increases in the availability of oxygen in the atmosphere and oceans there ought to have been a bursts of evolutionary radiation and diversity, but often oxygen-related causality for events such as the Cambrian Explosion have been speculative, as have cases for the inverse, declines due to downturns in oxygen levels (see Oxygen depletion before P-T extinction in the November 2003 issue of EPN). Recently a proxy for the redox chemistry of the global ocean, and therefore for relative changes in atmospheric oxygen, has been developed. It is based on the abundance and isotopic composition of the element molybdenum (Mo) in sedimentary rocks: higher 98Mo relative to 95Mo (the d98Mo value) signifies higher oxygen levels. Its recent use in relation to evolutionary radiations (Dahl, T.W. et al. 2010. Devonian rise in atmospheric oxygen correlated to the radiations of terrestrial plants and large predatory fish. Proceedings of the National Academy of the US, v. 107, p. 17911-17915) has produced interesting results. The US-Swedish-Danish-British team analysed the Mo in euxinic (reduced) marine black shales, which concentrate the element from seawater, in the Proterozoic and Phanerozoic Eons. Increases in δ98Mo occur at the time of the Cambrian Explosion, as expected, and also during the Devonian. The latter correlates with increasing diversification of large fishes and among early terrestrial plants, and may have been the greatest leap in the bioavailability of oxygen in Earth’s history, stemming from the ‘greening’ of the land. So far Mo-isotope data have not been obtained from Carboniferous, Permian or Cretaceous back shales, but the ratio of Mo to organic carbon content in black shales of those ages – a less constrained proxy – does confirm what has been suspected: highs (greater than present levels) in the Carboniferous and Cretaceous and lows during the Permian and Triassic. However, any hopes that the approach can be calibrated to actual oxygen levels seem likely to be optimistic as the controls over dissolved molybdenum supply to the oceans and its transfer to sediments are extremely complex.
Added 14 January 2011. Some of the team feature in a related article (Gill, B.C. et al. 2011. Geochemical evidence for widespread euxinia in the Later Cambrian ocean. Nature, v. 469, p. 80-83) that ticks all the geochemical boxes for the evolutionary effects of depleted oxygen; i.e. extinctions. They use new measurements of sulfur isotopes in conjunction with published carbon-isotope and other geochemical data from a wide range of Late Cambrian sediment types and environments in six well-known sections of that age. Spikes in the relative abundance of 34S match those in 13C along with a decrease in Mo in one section (see above), suggesting temporary increases in carbon and sulfide burial during periods of oxygen deficiency in the Late Cambrian ocean. Massive sequestration of organic carbon may have led to the extremely cold Late Cambrian climate, as described in A chilly Late Cambrian (this issue). Combined with changes in redox conditions associated with ocean anoxia this would have especially stressed animals, even on continental shelves had oxygen depleted water risen from the depths where sulfur and carbon burial were going on.
See also: Shields-Zhou, G. 2011. Toxic Cambrian oceans. Nature, v. 469, p. 42-43.
The notion that Neanderthals were dim and brutish compared with us continues to be undermined, but although their brain capacity was as large and in some cases distinctly larger than that of fully modern humans, its shape was significantly different; longer towards the rear than our more rounded brain. Studies of a Neanderthal baby and three children reveal that just after birth the Neanderthal brain was virtually identical to that of fully modern babies, i.e. elongate, but remains so in childhood through to maturity, whereas modern children’s brains develop towards the roundness of adults. Consequently, there must have been differences in the parts of the brain from which aspects of behaviour stem: Neanderthals almost certainly behaved differently from us both in childhood and as adults (Harvati, K. et al. 2010. Evolution of middle-late Pleistocene human cranio-facial form: a 3-D approach. Journal of Human Evolution, v. 59, p. 445-464. See also: Gibbons, A. 2010. Neandertal brain growth shows a head start for moderns. Science, v. 330, p. 900-901).
The now widely accepted hypothesis that modern humans did not begin to leave Africa to colonise Eurasia until about 60 ka may be under threat from reports of what seem to be fully modern human remains in China dated to ~105 ka (Liu, W. et al. 2010. Human remains from Zhirendong, South China, and modern human emergence in East Asia. Proceedings of the National Academy of the US, v. 107, p. 19201-19206). The dating appears to be sound, being based on the uranium-series (230Th) method applied to flowstone that rests on top of the sedimentary layer containing the remains in Zhirendong cave. The precipitated calcite layer completely sealed in the fossils as soon as it began to form about 105 ka ago, indicating that they are older still. Whether or not the remains are of fully modern humans is uncertain. Had they been found in Europe there would be little doubt about their affinities, the only other contemporary hominins being the Neanderthals. The problem in South China is that it was inhabited by H. erectus and the finds may be from ‘late’ members of that archaic species which arrived more than a million years earlier than fully modern humans. Judging by the DNA evidence for three interfertile hominin genetic groups cohabiting Eurasia, there is a host of possibilities for the Zhirendong fossils. One line of evidence that does not rule out that they are fully modern is the occurrence of stone tools more advanced than used by Asian H. erectus beneath the 74 ka Toba volcanic ash in India. It seems inevitable that these remains will be tried for DNA sequencing
See also: Dennell, R. 2010. Early Homo sapiens in China. Nature, v. 468, 512-513
It is well accepted that as with all forms of life the twists and turns in hominin evolution was surely tuned by changes in their environments. But that is not just linked to the immediate milieu of individuals: environments change on all scales up to that of the entire planet and reflect physical as well as biological processes. The largest scales are generally assumed to be the province of climate change, yet animals also occupy a landscape subject to geophysical forces such as tectonics and erosion. Geoffrey Bailey and Geoffrey King of the University of York, UK and the Institute de Physique du Globe in Paris, France have championed the view that water supplies and topography, for example, are just as influential over hominin evolution as interspecies competition and changing vegetation patterns for almost two decades. They have now put their ideas to rigorous tests (Bailey, G.N.& King, G.C., 2010 (in press) Dynamic landscapes and human dispersal patterns: Tectonics, coastlines, and the reconstruction of human habitats. Quaternary Science Reviews doi:10.1016/j.quascirev.2010.06.019). This fascinating and well illustrated paper correlates known hominin sites in Africa with variations in topography and its roughness, derived from global elevation data from the Shuttle Radar Topography Mission (SRTM), active seismicity, Neogene uplift and volcanicity.
Afar Depression: a cradle of human evolution
They concentrate on the rich palaeoanthropological pickings of the Afar Depression and the Sterkfontein area of South Africa, applying their ideas and findings to the eastern coast of the Red Sea at the recently discovered Palaeolithic site of Harat Al Birk south of Jeddah, and the Red Sea islands that would have been connected to either side of the Red Sea during the last glacial maximum because of a 130 m lower sea level. This application is vital for directing searches for new site that relate to the pathways out of Africa for early modern humans. Though a largely empirical study, it forms a link between human evolution and geological and landscape change that is not yet widely grasped and linked to climate studies.
See also: Marshall, M. 2010. Evolution by shake, rattle and roll. New Scientist, v. 208 (13 November 2010), p. 8-9.
The bulk of igneous rocks found within and upon the crust formed by one of two fundamental processes of magma differentiation: calc-alkaline and tholeiitic, responsible for island arcs and ultimately continents forming and for generating oceanic crust and flood basalts. The parental material for both is basaltic magma, but the first leads to a decrease in iron in more fractionated magmas, whereas an increase in iron characterised the second. In the first case conditions favour iron entering igneous minerals, whereas in the second they urge crystallising minerals to exclude iron. The most likely explanation is that the calc-alkaline magmas of volcanic arcs devour electrons so that iron exists in the oxidised ferric or Fe3+ state and readily forms dense iron oxide minerals whose progressive removal makes the remaining magma less and less rich in iron. More reducing conditions that lack an abundant electron acceptor, primarily oxygen, make the formation of iron oxides less likely, and iron can build up in residual magmas. But how greater oxidation occurs in arc magmas than in those of the oceanic crust has several possible explanations. The most-widely assumed is that it happens because volcanic arcs lie above subduction zones where hydrated and therefore oxidised ocean floor descends into the mantle conferring oxygen to the products of partial melting. Another candidate is the depth at which fractional crystallisation takes place and there are other possibilities. The oxidation state of fundamental magmatic processes can be proxied by determining in rocks produced by fractionation the relative proportions of elements that behave differently in conditions of increased or decreased oxygen. One such pair is insensitive zinc and sensitive iron (Lee, C.-T.A. et al. 2010. The redox state of arc mantle using Zn/Fe systematics. Nature, v. 468, p. 681-685). The surprise is that the parent magmas of both calc-alkaline and tholeiitic fractionation series have identical Zn/Fe ratios, suggesting that both partially melt from mantle with much the same availability of oxygen. The Zn/Fe ratios differ in more evolved igneous rocks from the two series, suggesting that it is in the fractionating magma chambers that the distinctively different oxygenation occurs, not in the zone of mantle melting.
Application of the Uniformitarian Principle by geologists from Minnesota, USA (Runkel, A.C. et al. 2010. Tropical shoreline ice in the late Cambrian: implications for Earth’s climate between the Cambrian Explosion and the Great Ordovician Biodiversification Event. GSA Today v.20 (November 2010), p. 4-10) may have shown that around the end of the Cambrian period (500 to 488 Ma) global climate was sufficiently cold for sea ice to have formed in the tropics of the time. The evidence comes from curious metre-scale clasts of cemented sands in Late Cambrian beach deposits of the northern USA, some of which show imbrication as if the bodies were shoved together. Others seem to have been extended into boudin-like plates without any sign of tectonic activity, so that isolated clasts occur in offshore deposits. Yet more have been bent to drape over irregularities in the surface beneath them. Somehow individual sand beds must have become cemented quickly so that water action could fracture them in a brittle fashion and then they became softer to experience ductile deformation and even boring by worm-like animals. Almost exact replicas of such structures form on the shores of the American Great Lakes in winter when water in shoreline sands freezes to cement the grains. Breaking waves and melting explain the peculiar structures in these intraclasts. Examples of ice-cemented sediments abound in glaciogenic deposits, but the Late Cambrian world is widely considered to have experienced greenhouse conditions.
Image via Wikipedia
Apparently not as the North American crust was definitely close to the Equator at that time. The intraclasts occur only in one stratigraphic Formation of the Minnesotan Cambrian, because it preserves littoral facies. There are no other reports from elsewhere, but that may well be because few geologists were able to combine the experience of modern frigid shore conditions with that of Cambrian stratigraphy as those from Minnesota surely do.
The Middle to Late Cambrian was a period of faunal hiccups, diversification after the Cambrian Explosion failing to get underway because of repeated minor extinctions spread across the known occurrences of rocks of that age (see Linking oxygen levels to great animal radiations, this issue). The Minnesotan evidence could indicate that the global climate was extremely unstable at that time in the manner of Neoproterozoic ‘Snowball Earth’ conditions, but not so severe. The widespread occurrence of microbial carbonate facies of this age range has long been used as evidence of a warm Earth, but such carbonated form today over a wide range of latitudes: witness the huge coccolithophore blooms so common at high latitudes nowadays. Shoreline sandy sediments of Cambrian age are not uncommon, occurring throughout the English Midlands and in NW Scotland, for instance. So it might be interesting to re-examine easily-reached occurrences such as these to see if similar structures turn-up.
As the temperature and pressure affecting crustal rocks go up and down, as for instance in the thickening of crust when two continents collide and then erosion strips off the cover so that the rocks slowly rise, the rocks undergo progressive changes in their mineral content; in both cases they are metamorphosed. Rising intensity of conditions gives rise to a prograde metamorphic sequence, and when they wane retrograde metamorphism takes place as the elements that combine in minerals react to adjust to new conditions. In some cases it is possible to use the mineral assemblages, specifically the proportions of different elements that are shared between two or more minerals, to chart the changes in temperature and pressure. That reveals the path taken by the rock through temperature- and pressure space, which is effectively a measure of the crustal processes involved and the geothermal conditions under which they acted: a P-T path. Adding the timing to give a sort of movie to all the changes has been hit-or-miss up to now, and based on radiometric ages from igneous rocks formed and emplaced during the metamorphic evolution. Thanks to the finely targeted mass spectrometry that an ion microprobe an achieve, adding the ‘t’ dimension is now possible from the metamorphic rocks themselves (Sajeev, K. et al. 2010. Sensitive high-resolution ion microprobe U-Pb dating of prograde and retrograde ultrahigh-temperature metamorphism exemplified by Sri Lankan granulites. Geology, v. 38, p. 971-974). Minerals based on the element zirconium (Zr), such as zircon and monazite are extremely resistant to the effects of temperature as regards the radioactive and radiogenic elements that they contain, specifically uranium (U) and thorium (Th) and the lead (Pb) isotopes that form when 235U, 238U and 232Th decay. Both these minerals become zoned as successive layers grow during metamorphism, and the ion microprobe can measure the isotopic composition on a later-by-layer and therefore event-by-event basis. The famous granulites (charnockites) of the island of Sri Lanka (Ceylon) reached the peak of their metamorphism (1050°C and 0.9 GPa) at ~570 Ma and began to retrogress about 20 Ma later around the start of the Cambrian. Previously it was not possible to separate metamorphic ages from those when the original rocks formed in the Archaean and early Neoproterozoic. Such high temperatures are very difficult to attain in the crust under normal geothermal conditions unless extra heat is added by large volumes of basaltic magma ponding at the base of the crust during crustal thickening.
Methane hydrates – natural gas held in clathrate solids that resemble water ice – that occur in sea-floor sediments are on the one hand a potential energy resource and on the other pose great risks. There are between 1015 to 1017 m3 buried beneath the ocean floors and an unknown amount in Arctic soils and lakes. The temperature that confers stability on these peculiar solids depends on pressure. At pressures lower than those at a water depth of around 250m they are unstable. Clathrate crystals form from natural gas and water in sediments at 0°C at that depth and at progressively higher temperatures at deeper levels beneath the seafloor, until geothermal heat flow at a depth of around 2.5 km results in temperatures above about 20°C when they cannot form; there is a depth-temperature window in which gas hydrates may be found in seafloor sediments, which depends on the temperature of deep water. Little is known about the stability of gas hydrates. In some areas there is a steady release of methane that bubbles to the surface, whereas in others they can be detected by seismic surveys in huge volumes that appear to be stable with no release. One area rich in gas hydrates occurs at the continental edge off the Norwegian coast (the Storeggain Norwegian). Periodically sediments at the Storegga fail in massive sub-sea landslides which have resulted in tsunamis in the North Sea. The last such tsunami occurred around 6100 BCE after a slide displaced 3500 km3 of debris, devastating the east coast of Scotland. Either an earthquake triggered the slide or it was due to destabilizing of the clathrates. Either way huge amounts of methane would have been released. At the end of the Palaeocene Era (55 Ma) a global carbon-isotope anomaly coincides with evidence for very rapid climatic warming, which suggests that vast amounts of methane – a far more powerful greenhouse gas than CO2 – were released from submarine gas hydrates. In recent years the loss without trace of several large ships may have resulted from a lowering in the density of surface water by gas bubbles that caused the vessels to founder. One country that plans to exploit gas hydrates off its Pacific cast is Japan, and recent surveys indicate a large basin underlain by highly disturbed sediments which contain clathrates on the flank of the basin (Bangs, N.L. et al. 2010. Massive methane release triggered by seafloor erosion offshore southwestern Japan. Geology, v. 38, p. 1019-1022). It appears that bottom currents eroded the seafloor to destabilize the clathrates that then ‘erupted’ ripping through the sediments to release around 1.5 x 1011 m3 of methane. Clearly, drilling into gas hydrate deposits is going to be a risky business; drilling will reduce the pressure so that gas is released and it is not known whether or not this might trigger a form of chain reaction. In the longer term, warming of deep water as a result of climate change could place much larger areas of clathrate-rich seafloor in a knife edge.
Though it is highly likely that burial of fossils for millions of years destroys any trace of their DNA the massive bones of large creatures can preserve cell material. A near complete 67 Ma old Tyrannosaurus rex, fondly known as ‘Big Mike’ has revealed blood cells in thin sections of its bone (Schweitzer, M.H. 2010. Blood from stone. Scientific American, v. 303 (November 2010), p. 38-45). Her article also covers traces of blood vessels, and collagen of similar antiquity. The research involved positive reaction of antibodies against proteins, thereby proving the materials to be organic and not products of biomineralisation formed during the process of fossilisation. Potentially such forensic work can tease out relationships among animal groups whose fossils preserve organic materials, in a similar way to indications of the rise of prokaryote groups by biogeochemical marker molecules in carbonaceous shales. Indeed, sequences of fossil proteins from dinosaurs closely resemble that of modern birds. One of the great surprises of the late 20th century was the growing evidence that the stem-line for birds was dinosaurian, specifically the theropod group. This is nicely summarized by another review article (O’Donoghue, J. 2010. Flight of the living dead. New Scientist, v. 208 (11 December 2010), p. 36-40) that addresses the certainty of birds’ evolution from dinosaurs; which of the fossils is bird, which feathered dinosaur and when did they separate; and why did birds survive the end-Cretaceous mass extinction while dinosaurs famously succumbed – probably a matter of breeding; its pace, that is. The two articles together suggest a fruitful way forward for palaeobiologists.
Further material about biochemical relics in fossils and methods used to detect and analyse them can be found in Hecht, J. 2011. Waking the dead. New Scientist, v. 209 (22 January 2011 issue), p. 43-45.
Every geoscientist will salute the fortitude and bravery of the 33 Chilean miners rescued from a refuge 700 m below ground, that of the 5 volunteer rescuers who descended the 80 cm shaft, not knowing whether it was safe and the skills of voluntary engineers whose drill managed to find the small refuge, despite its depth. Many geologists have been in underground mines, though only a minority have worked in them, but all admire the mental and physical resilience of the 33. Trapped by the caved-in access tunnel on 5 August, the miners faced and survived 17 days with fading lamps and tiny supplies of food and liquids. The final rescue came with remarkable swiftness during 13-14 October. Apart from one with a chest infection all seemed little the worse for wear. The growing tension during the rescue was almost palpable, even at a distance of more than 11 000 km: would the narrow tunnel collapse; would the rescue shuttle jam? The likelihood of either grew with each rescue.
The rise in gold and copper price since the global crash of 2008 has seen the reopening of dozens of once uneconomic mines, kept for years on a ‘care and maintenance’ basis. Not knowing when the metal-price boom would collapse, mine owners have rushed to restart operations, paying locally premium wages to attract miners. The San José mine near Copiapo, was one such mine, whose fabric had deteriorated after years of neglect. It would be unsurprising if another disaster, with less happy outcomes, occurred during the current metal-mining boom.
Added 26/11/2010. So soon after such a victory over being buried alive for so long, it is especially tragic to learn that the methane explosion of 19 November in New Zealand’s largest coalmine at Pike River on the South Island killed 29 miners. They were declared dead after a second explosion on 24 November. Today a third blast ripped through the mine not long before a memorial service was to be held, vindicating the decision not to send in rescue parties as soon as the initial explosion took place. Inevitably, there will be a major inquiry into how such a build-up of explosive gas could possibly have gone unnoticed.
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