Author: zooks777

Former Senior Lecturer at British Open University, research in remote sensing of arid lands, groundwater exploration, Precambrian tectonics and geochemistry

Watch out, watch out, there are burglars about

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f the major journals are anything to go by, the gravest crime that scientists can commit is to make up data and publish the results after peer review. The only thing worse in the eyes of us ‘academics’ is to publish the same makey-up data several times without being rumbled by referees. Once discovered, all the hammers of hell fall on the miscreant: they lose their jobs; their faces are splashed on the news pages of Nature and Science; they are blackballed internationally and can never work in academic circles again. Pretty harsh treatment for what, after all, is a good old-fashioned con (and often one of some ingenuity). In general, most of us love a rascally grifter, so long as they haven’t trousered our life savings. So why is the academic equivalent of the death penalty reserved for what is little different from getting a gullible public to believe that politicians act in the best interests of humanity? If any geologist looked deeply into his or her conscience most would find several cases where they had fudged a bit of data – marked a geological boundary on a map where there was barely a shred of evidence, for instance. We have all speculated well beyond the realms of reality, and often that has passed peer review easily. It is in the very nature of a dominantly observational science to do the odd bit of grifting and have it accepted.

What we detest in real life is the burglar, who desecrates our homes and work. Having anything stolen leaves a life-long trauma and a feeling of being somehow dirtied. In our academic world, theft is called plagiarism. It is most generally applied these days to the actions of students who snip bits and pieces from published sources to get a good mark from a term-paper or dissertation. Like the fabricator of data, they are generally hammered if caught at it. Yet there is a real theft that damages its victims rather than merely soiling the ‘clean image’ of education, and these victims are usually ‘junior partners’ in research. It is rife, and in one form is actually condoned and even encouraged. These days many research students are forced to more or less sign away their intellectual property to their supervisors, often a sizeable posse most of whom do very little, if anything at all. If a research student wants to publish the posse must be in the list of authors. Many commentators have noted that this riding on the backs of the inexperienced is how CVs are built up and fast-track promotion is achieved. It could be called the ‘pillion passenger’ route to greatness. But this kind of institutionalised pillaging is by no means the worst form that plagiarism can take. Far worse is to find out accidentally that one’s original ideas, data, or graphics are being published or uttered by someone else without any acknowledgement, especially if they have yet to be published.

The police rarely catch a burglar, and even less-often recover stolen goods. Similarly, victims of this worst form of academic plagiarism also know that having the record properly set straight is unlikely. The academic burglar excuses him/herself with the defence that, “there is no copyright over ideas”. To accuse such charlatans invites being actioned for libel, because of legal vagueness over intellectual property. Last month I witnessed an attempted burglary at a conference in London. In that case the burglar not only published purloined ideas previously but clearly fed his student those ideas. Unwittingly, she presented them, suitably tarted up, but with him as second author – i.e. trying to have his cake and eat it. All would have gone smoothly for the snaffler, but for one thing. The victim was there and gave the genuine presentation only 30 minutes before the blagged one hit the floor. Quite clearly, she knew what she was talking about whereas the coached presenter obviously did not. Thanks to two or three acute, and honest people in the audience, the game was up. The perpetrator of the burglary was, in the most polite (and legal) fashion, academically savaged with not inconsiderable relish. In a way, justice was done, but not entirely.

Anyone who attempts to build a career by theft needs to be stopped in their tracks, but in the ‘halls of academe’ only con-artists who are caught have the book thrown at them. So, keep your eyes and ears open in 2008, on behalf of others as well as yourself, for that is the only way metaphorically to give burglars a touch of the old Black and Decker about the knee caps.

Neoproterozoic climate modelling supports a ‘slushball’ Earth

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Following its first discovery, evidence for low-latitude glacial action at several times during the Neoproterozoic has fuelled one of the most publicised controversies in the geosciences. Was the Earth totally frozen over during these episodes, or was ice confined only to parts of the surface? Whatever, the last part of the Precambrian witnessed huge fluctuations of many kinds, and after the cold epochs the first large animals made a sudden appearance. The most dramatic geochemical ups and downs in Earth history took place, in the form of sudden extreme shifts in the relative proportions of the stable isotopes of carbon in seawater, as recorded by marine carbonate rocks. These fluctuations correlate closely with the evidence for low-latitude glaciations: large negative excursions of d13C with glacial epochs, and positive values developing between them. The first can be interpreted as the result of massive declines in photosynthetic fixation of organic carbon. The second suggests repeated recoveries of such biological productivity, which favours the extraction of 12C from seawater and an increase in the relative proportion of the heavier isotope as organic carbon becomes buried in seafloor sediments.

Since organic carbon is ultimately extracted photosynthetically from carbon dioxide in the atmosphere, a link between climate and living processes (and those that bury dead organisms) can be the basis for models attempting to explain the extraordinary events of Neoproterozoic times. If large amounts of organic carbon are buried or remain suspended in the oceans, the drawdown of atmospheric CO2 reduces the greenhouse effect and leads to cooling. Conceivably, the effect could be to so reduce global mean surface temperature that freezing conditions grip even the lowest latitudes. Once glacial and sea ice becomes established, its high reflectivity reduces the amount of incoming solar radiation that is absorbed to warm the Earth. The two processes combined would tend to lock frigid conditions in place until such time as gradual release of volcanic CO2 increased the atmospheric greenhouse effect. That is the theoretical essence of the Snowball Earth hypothesis in which complete ice cover sterilised surface biology for long periods. However, it leaves out two important factors: as water cools it is able to dissolve more gases from the atmosphere; organic carbon in ocean water can be transformed to dissolved CO2 if it is oxidised, thereby reducing the amount of carbon being buried. Modelling the carbon-climate link in the Neoproterozoic requires that both factors are accounted for (Peltier et al. 2007. Snowball Earth prevention by dissolved organic carbon remineralization. Nature, v. 450, p. 813-818).

The model devised by Richard Peltier and colleagues from the University of Toronto also incorporates the distribution of land at the time. Results from it show a looping behaviour, with recovery from frigidity as increases in dissolved oxygen convert organic carbon to dissolved carbon dioxide, whose increasing concentration in turn leads to more escape of the gas to the atmosphere. The model also suggests how glacial and sea ice might have developed during such a cycle, and with the late Precambrian configuration of drifting continents it allows for low-latitude continental glaciation, but not for all-enveloping sea ice. The implication is indeed glacial events vastly greater than those of the late Palaeozoic and during the present Ice Age, but less effect on marine photosynthesis than from Snowball conditions – a ‘Slushball’ Peltier et al. explain why the cyclical processes suggested by the model stopped before the start of the Phanerozoic, from carbon-isotope evidence for a massive oxidation of suspended marine organic carbon around 550 Ma. Thereafter, abundant oxygen and large animals ensured most dead organic carbon was oxidised in the oceans.

Unsurprisingly, one of the authors of the Snowball hypothesis finds flaws in the geochemical argument for its impossibility (Kaufman, A.J. 2007. Slush find. Nature, v. 450, p. 807-808). Not only was oxygen likely to have been at far lower atmospheric concentrations than it became in the Phanerozoic, the glacial epochs provide evidence that its concentration in seawater was very low. The marine diamictites associated with each contain both ironstones and iron-oxide cements. For them to have formed demands high concentrations of dissolved iron in sea water, in the form of reduced Fe2+ ions; incompatible with widespread oxidizing conditions that would favour Fe3+ whose compounds are insoluble.

Some good news about carbon burial

The second largest ‘sink’ for atmospheric CO2, after silicate weathering and formation of carbonate sediments, is the burial of organic carbon. Derived from photosynthesis of carbon dioxide in the air or dissolved in water, organic carbon descends from the photic zone of the oceans or is carried from the land by rivers. In the second case it is often believed that more than 70% of the carbon load of rivers is oxidised back to CO2 before having a chance of being buried in marine sediments. To estimate the proportion that does contribute to carbon sequestration is a complicated matter, involving measurement of the carbon budgeting for an entire river basin and its offshore sediments. This has been done by a team of French geochemists for the huge Ganges-Brahmaputra system that drains the northern Indian subcontinent and much of the Himalaya (Galy, V. et al. 2007. Efficient carbon burial in the Bengal fan sustained by the Himalayan erosional system. Nature, v. 450, p. 407-410). This system carries a stupendous load of sediment, especially during the monsoon season. At 1 to 2 billion t of sediment deposited from suspension in the Bay of Bengal each year, this is the largest single flux of sediment from land to the ocean floor. Even more is delivered as bed load (rolling and bouncing sand particles) to build up the Ganges-Brahmaputra delta of Bangladesh and West Bengal, India. The authors found that recently produced organic carbon is about 4 to 5 times more abundant in the suspended sediment load than is reworked fossil carbon derived by erosion of ancient sedimentary rocks, which itself is predominant in the bed load. Fossil carbon makes no difference to the modern carbon cycle, provided it does not get oxidised, which is less likely than for recent organic carbon in a form that can be metabolised.

By comparing the recent organic carbon load suspended in the rivers’ flow with that in the fine sediments of the Bengal Fan, Galy et al. have been able to show that most of that carbon is conserved without oxidation. As a result, the Bengal Fan accounts annually for about 15% of global carbon burial. There are two reasons for this remarkable efficiency: the low oxygen availability in deep waters of the Bay of Bengal; the very high sediment load from erosion of the Himalaya that buries carbon before oxidation is possible. Orogenic belts in humid areas are therefore key factors in exerting negative feedback on climate, whereas drainages of flat areas, such as the Amazon and especially its main tributary the Rio Negro, encourage oxidation in their lower reaches and offshore and are less important.

Moon formed from vapour cloud

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The Moon is generally believed to have formed from the debris ejected when a body (nicknamed Theia) about the size of Mars struck the partly formed Earth a glancing blow. That cataclysmic event can be considered to have marked the start of geochemical evolution of both Earth and Moon. From a purely mechanical standpoint, it seems almost inevitable that the Moon is made mainly from debris supplied by the offending small planet. Yet Earth and Moon have some profound geochemical similarities, the most remarkable being their now similar blend of oxygen isotopes. Meteorite studies suggest that oxygen isotopes varied widely in the early Solar System, probably differing according to distance from the Sun. That suggests that the Earth-Moon similarity is somewhat odd, unless the impacting planet formed in the same part of space as the Earth itself, i.e. in a very similar orbit. However, that is as mechanically unlikely as the Moon being a chunk of Earth flung off by the impact.

A new explanation for shared oxygen isotopes is based on a model for the collision that involves the vaporisation of most of the Earth and Theia (Pahlevan, K. & Stevenson, D.J. 2007. Equilibration in the aftermath of the lunar-forming giant impact. Earth and Planetary Science Letters. v. 262, p. 438–449). High temperature vapour would have involved sufficient turbulence for the geochemical signatures of both Earth and Theia to have been mixed efficiently.  The Moon would then have condensed from a disk of orbiting vapour of this mixed composition, most of the Earth re-accreting in a molten state too. Thus both bodies would have begun their evolution with deep magma oceans. The light-coloured, highland part of the Moon is thought to be a relic of the flotation of plagioclase crystals that floated to the top of its magma ocean as it began to cool; the lunar highlands are made of anorthosite and are at least 4.4Ga old. So far no tangible sign of such relics of early fractionation have appeared in the Earth’s geological record. Pahlevan and Stevenson’s model indicates that only between 100 to 1000 years would have elapsed from impact to appearance of the moon as a tangible body.

Another angle on the mysteries of the Hadean

Geochemists will be celebrating the end of 2007 after a steady growth in knowledge about times before formation of the first real rocks, albeit of a proxy nature. The latest addition stems from the isotopes of the rare-earth element neodymium. Its heaviest isotope 144Nd is a direct product of nucleosynthesis in supernova star explosions The middleweight isotope 143Nd is well-known as the daughter product of the decay of one unstable isotope of a sister element, samarium (147Sm, half-life 1.06 x 105 Ma). The Sm-Nd dating method, based on this decay, has been an important means of dating ancient mafic and ultramafic rocks and examining the geochemistry of their source rocks in the mantle for over 20 years. The lightest isotope is also a daughter of radioactive decay but would have formed from short-lived 146Sm (108 Ma half life). Potentially, 142Nd in old rocks can be used to judge processes in the Hadean mantle as 146Sm would have declined rapidly in the early Solar System – none is detectable nowadays. In meteorites it reveals complexities in the early differentiation of their parental planetesimals, and lunar studies show that too was subject to fractionation. That something odd happened in the early Earth became apparent when it was discovered that modern crust and mantle had more radiogenic 142Nd than the chondritic meteorites thought to have been the building blocks for the Earth. A study of neodymium isotopes in the two largest old chunks of continental crust – the  Archaean gneisses of SW Greenland and Western Australia – revealed yet more (Bennett, V.C. et al. 2007. Coupled 142Nd-143Nd   isotopic evidence for Hadean mantle dynamics. Science, v. 318, p. 1907-1910). The two blocks are different as regards their neodymium, and this suggests that a fundamental chemical division of the Earth’s mantle took place during the Hadean, which lasted for the next billion years at least. Yet another long-held idea about the Earth’s origin seems condemned to the status of myth. It had been assumed that the early Earth was well-mixed as a result of its accretion from countless planetesimals – it doesn’t really matter if they included different varieties because accretion would have been such a chaotic process. Discovering whether the now-established mantle fractionation resulted during accretion or after a cataclysmic collision with another world formed the Earth-Moon system is set to be the next challenge for students of the Hadean. It will probably be argued that this requires yet more samples to be brought from the Moon…

Last common ancestor of all the primates was a flying lemur

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Vertebrate palaeontologists sometimes become precious after a career peering at old bones, especially when they are as remarkably tiny as those of most Mesozoic mammals – and most of those fossils are teeth. Some defend to death the notion that primates descend from tree-shrews, while others foam at the mouth at the mere suggestion of the ur-shrew. ‘A key feature in primate evolution is reduction of the snout’, is axiomatic to yet others. Again, geneticists have provided extreme selection pressures that will either cause vertebrate palaeontologists rapidly to evolve or to become extinct.

Analysis of living primate genomes produces a phylogeny that links all primates with a group that has been said to be ‘the sort of animals that defy taxonomic categorization, confuse one’s sense of aesthetics, and seem to largely fall under the umbrella of “weird.” ‘ (Janecka, J.E and 7 others 2007. Molecular and genomic data identify the closest living relatives of primates. Science, v. 318, p. 792-794). These are the colugos, or flying lemurs that include the wonderfully named sugar glider.

Planet of the beetles

More than 20% of the known diversity of life on Earth is made up by the order Coleoptera, which includes several hundred thousand species. Although that huge number is largely thanks to beetle collectors, Charles Darwin having been a particularly voracious one, it is difficult believe that any other order or even class of multicelled organisms will prove to be as diverse. Yet there is only a sparse fossil record of these ubiquitous creepy-crawlies. The earliest known beetle fossils date back to the Lower Permian, and the Triassic saw their radiation into wood-eating, predatory and fungus-eating clades – from morphological similarities with living beetles. Their modern diversity depends on the vast range of ecological niches that beetles can fill, many of which are environmentally so subtle that only the beetles exploiting them show that the niches exist at all. Like all organisms the evolution of the beetles has been within the interconnectedness of the whole Earth system, and it through the linkages that such subtlety has emerged and evolved. One of the best known is the sensitivity of different beetle species to small climatic changes, which has allowed their growing use for charting climate change on land: they are far better proxies for temperature than are the foraminifera of the oceans.

Being only sparingly preserved in rocks, how beetles evolved has long been a mystery, considering their overwhelming presence on the planet. Yet again, the rapid rise of molecular phylogeny, including means of timing when mutations took place, is starting to supplant the skills of the traditional palaeontologist (Hunt, T. and 15 others 2007. A comprehensive phylogeny of beetles reveals the evolutionary origins of a superradiation. Science, v. 318, p. 1913-1916). Toby Hunt of London’s Natural History Museum and colleagues from the UK, Czech Republic, USA, Germany and Spain have combined their own RNA sequencing with existing databases of 1880 species from all the beetle suborders, series and superfamilies, 80% of families and 60% of subfamilies, to represent more than 95% of all described species. This establishes a phylogenetic tree for the lineages that they analysed, details of which will excite the coleopterist sororities and fraternities. The general picture, however, presents a more a broadly fascinating surprise. Because a vast number of beetles are associated with plants and fungi, it might seem inevitable that their evolution has parallels with that of plants, especially their explosive diversification once the angiosperms  (flowering plants) appeared. The molecular dating clearly shows that is not the case. While the angiosperms emerged in the Cretaceous Period, more than 100 living beetle lineages appeared earlier in the geological record. Unlike the Vertebrata, which diversified after mass extinctions (including the primates), the fundamental beetle lineages were clearly good survivors that were capable of their own diversification whenever opportunities arose. I think we might grow to worry about that…

Mammal evolution makeover

The Cenozoic has been the Era of mammals, and their diversification is the largest recorded adaptive radiation. However, the Linnean names of many mammal clades from the Mesozoic end in ..dont, i.e. they have been defined in terms of their teeth and not much else.  Most fossil mammals from the Mesozoic are small and fragile and only survive as teeth and jaw fragments. As a result most of the course of early mammal evolution has been a bit uncertain, to say the least. The view until recently has been that early mammalian evolution was a step-by-step affair in which key innovations accumulated in an orderly manner.  However, even on the basis of teeth, developing taxonomic approaches have proved able to reveal that considerably more complicated things happened (Luo, Z-X. 2007. Transformation and diversification in early mammal evolution. Nature, v. 450, p. 1011-1019). For a start, it turns out that mammals, despite their scanty remains, were almost as diverse during the Mesozoic as the dinosaurs that are often said to have driven early mammals underground or into the night (310 mammal to about 550 dinosaur genera). The potential for analysis stems from an explosive growth in fossil discoveries: from 116 genera in 1979 to the present 310, and a 200-fold increase in well-preserved specimens. Clearly, mammal-oriented palaeobiologists have been hard at work.

Zhe-Xi Luo of the Carnegie Museum of Natural History in Pittsburgh crams most of the developments into a 6-page review, from which it is possible to learn a great deal, albeit needing quite a firm grasp of cladistic terminology. One of the highlights is how evolution of the mammals before 65 Ma involved repeated evolutionary convergence, i.e. the end products of evolutionary bursts often looked superficially similar. That tendency carried over into the Cenozoic on a grander scale. One example is that of adaptations for burrowing to produce mole-like end products, even some with semi-aquatic habits. Many of the rapid diversifications ended in extinction of the lineage, but all seem to indicate a great deal of ‘experimentation’ with a range of original forms that channelled towards similar functions. The outcome was a vigorous occupation of potential ecological niches in which mammals clearly had the advantage over reptiles, possibly because of their physiologically greater adaptability, partly stemming from warm-bloodedness.

Permian shark bites fish-biting amphibian

It is worth queuing to await the appearance of the 22 January 2008 issue of the Proceedings of the Royal Society B: Biological Sciences. It contains unique evidence of predator-prey relations and the food chain in the Lower Permian Zechstein Sea (Kriwet, J. et al. 2008. First direct evidence of a vertebrate three-level trophic chain in the fossil record. Proceedings of the Royal Society B: Biological Sciences, v. 275, p. 181-186). The object for your amazement is a shark whose gut contains two amphibians. The last meal of one of the amphibians was a small fish.

The paper promises to be reminiscent of the final part of the Monty Python Fish Slap Dance sketch, which can be viewed at http://www.youtube.com/watch?v=d1xfp6Xeu0c&feature=related

Neanderthals more ‘human’ than once thought

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Sébastien Chabal, the gigantic and hairy back-row forward in the 2007 French World Cup rugby team, was nicknamed ‘The Caveman’ by French fans. Indeed he is an awesome spectacle, at almost 2 m tall and weighing over a tenth of a tonne, with great black beard and locks. But is seems that Neanderthals were redheads and probably prone to sunburn (Lalueza-Fox, C. and 16 others. 2007. A melanocortin 1 receptor allele suggests varying pigmentation among Neanderthals. Science, v.  318, p, 1453-1455). The team analysed DNA extracted from Neanderthal bones from Spain and Italy, and identified the mc1r gene that regulates pigmentation in many mammals. In both specimens it turned out to be a variant that is associated with fair skin and red hair. An artist has rendered a French Neanderthal man’s physiognomy from his skull, by combining this information with modern facial reconstruction techniques (in Culotta, E. 2007. Ancient DNA reveals Neandertals with red hair, fair complexions. Science, v. 318, p. 546-547). He seems set to become a pin-up among those ladies who favour the larger gentleman, even having a nose far larger than that of Gerard Depardieu. Although proof of the growing power of genetic analysis of ancient tissue, that Neanderthals were probably pale-skinned is not really surprising. They inhabited high latitudes for at least 200 ka longer than modern Europeans have, and the pale variant of mc1r is advantageous where sunlight is at a premium for creating vitamin D. Like modern Europeans, their immediate ancestors who migrated northwards were almost certainly dark-skinned.

Yet by far the most scientifically exciting outcome of the team’s work is the extraction from the Spanish Neanderthal bones of the FOXP2 gene, which is implicated in the development of speech and language (Krause, J. and 12 others 2007. The derived FOXP2 variant of modern humans was shared with Neandertals. Current Biology, v. 17, p. 1908-1912). It shares two mutations with FOXP2 in modern humans, that had previously been suggested only to have developed in the last 100 ka, so must have been present in the last common ancestor of fully modern humans and Neanderthals, around 300 to 400 ka. Although this discovery cannot prove that Neanderthals spoke, taken along with emerging evidence that symbolic skills were used by even earlier hominins (see When and where ‘culture’ began in November 2007 issue of EPN) it does suggest they were capable of as much sophistication as the earliest fully modern humans.

Is human evolution speeding up?

Another outcome of the acceleration in genetic analysis is an ability to scan vast numbers of differences in DNA from many individuals.  Highly productive are single nucleotide polymorphisms or SNPs (‘snips’) that are available from the international HapMap project. From analysing almost 4 million SNPs from 270 individuals has emerged an intriguing parallel between human population explosion since about 40 ka and an increasing rate at which new genetic traits have been incorporated into the human genome (Hawks, J. et al. 2007. Recent acceleration of human adaptive evolution. Proceedings of the National Academy of Sciences, v. 104, p. 20753-20758). The link is not entirely surprising, for the exposure of more individuals to mutagenic factors will result in more mutations entering the total gene pool. Yet ‘weeding-out’ of unfavourable mutations also operates over time, so the fact that around 7 % of human genes seem to have changed over the last 40 ka, indicates the overall rate of human evolution must have speeded up remarkably. The analysis suggests that the rate rose to a peak between 5000 and 8000 years ago, for Europeans and West Africans respectively. ‘Received wisdom’ has for a long while been that fully modern humans went through a phenomenal spurt in evolution around 50 to 40 ka (but see When and where ‘culture’ began in November 2007 issue of EPN), and that somewhat Eurocentric view is overturned by the SNP evidence. Selection pressures must have risen to a peak around the time of the spread of agriculture and the rise of large social communities – big changes in diet and in exposure to communicable disease would be associated with those shifts.

In some respects the findings are cause for optimism. Global warming and rapid transformation of climate belts will expose billions of people to new experiences. Hundreds of millions, or more, may perish, yet our species’ evolution may speed up again. Let’s hope it leads to some improvement in avoiding self-induced misfortune.

See also: Holzman, D. 2007. How we adapted to a modern world. New Scientist, v. 196, 15 Dec 2007 issue, p. 8-9.

A shocking discovery

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Every introductory geology course hammers home the message that the finer the grains in a sedimentary rock, the lower the energy under which it was deposited. This ‘received wisdom’ links to the ways in which grains move in moving fluids: rolling; bouncing and in suspension. A reductionist view sees this as the influence of Stokes’ Law in the boundary conditions between turbulent and laminar flow, close to the bed of flow and higher up in the fluid respectively. Stokes’ Law is invoked as that explains how spheres falling through fluids reach a steady speed related to the fluid’s viscosity. The larger the radius of the sphere, the greater that settling speed is. For the smaller size ranges settling speed is proportional to the square of the radius (laminar flow conditions), whereas for large objects it is proportional to the square root of radius (turbulent flow).  This nicely explains the upward decreasing grain sizes in graded beds, formed when a mixture of grain sizes settles from moving fluids when their speed slow, as in turbidites and the on the lee sides of sand dunes. Since we often see silts and muds being deposited in low-energy lagoons and estuaries on the coast that too seems to verify the theory. However, muds that contain clay mineral particles are quite different from scaled-down spherical grains: they are platy; often have unbalanced electrical charges and are subject to Brownian motion that helps keep them in suspension.  When clays suspended in fresh river water meet the sea, ions in sea water encourage the plates to clump together as aggregates or floccules that are much larger than the clay particles themselves. Another oddity is that, once deposited, clays are not as easily eroded as uncemented sands, partly due to their hosting biofilms that hold the particles together.

Despite the accepted explanation of mudstones as indicators of past low-energy conditions based on reductionist notions, suspicion of awkward complexity dates back to Henry Clifton Sorby, one of the founders of geology, who suggested that the study of mudstones and shales was a great challenge for sedimentology. In reality there are probably more than 30 parameters that govern the shifting and deposition of muds, many bound up with flocculation. Confidently discussing the true environmental conditions of mudstone deposition is often thwarted by their ease of weathering and by small animals that munch their way through muds to exploit often high contents of organic debris. Even the fissility of shales is a mystery in the field. Now and again, muds do reveal surprises, such as ripples and cross lamination, that surely reflect current action. Only experimentation can throw light on Sorby’s great challenge (Schieber, J. et al. 2007. Accretion of mudstone beds from migrating floccule ripples. Science, v. 318, p. 1760-1763). Schieber and colleagues from MIT and Indiana University used experimental flumes to investigate what happens to clay floccules, seeding the materials with fine hematite grains to show up any bedforms clearly. The muds used were from 5 to 63 mm in size, which produced floccules between 0.1 to 1.0 mm.  Again and again the experiments produced migrating ripples, some like tiny barchan dunes made of clay floccules. The surprise lay in the flow speeds at which they began to form: between 10 to 30 cm s-1, much the same as those needed to produce sand ripples. Floccules were preserved in the experiments, but since they are made of clay minerals, compaction tends to destroy floccule outlines when mudstones form.

No doubt some fine-grained sedimentary rocks reflect low-energy environments, but without more careful examination of their small-scale features muds formed by energies as high as those involved in producing sandstones and many limestones will go unnoticed. Since mudstones are the most common sedimentary rocks in the geological record, some big surprises are in store.

See also: MacQuaker, J.H.S. & Bohacs, K.M. 2007. On the accumulation of mud. Science, v. 318, p. 1734-1735.

Detecting, mapping and understanding ancient soils

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A recent paper provides a clear guide and a new means of addressing one of geoscience’s great puzzles (Andrew Deller, M.E. 2006. Facies discrimination in laterites using Landsat Thematic Mapper, ASTER and ALI data — examples from Eritrea and Arabia. International Journal of Remote Sensing, v. 27, p. 2389–2409). During the early Cenozoic, and perhaps before that, huge areas of the exposed continental surface were subject to a hot, humid climate. Intense chemical weathering broke down every conceivable rock type to a few stable minerals. The resulting residual soils were preserved over vast areas of Africa, South America, India and Australia to form laterites, which M.E. Andrews Deller at the Open University UK points out are distinctly zoned [avoids repeat of layered] mineralogically and stunningly layered in colour. No one can fail to see laterites where they are exposed, if they know what to look for, but few geologists have set out to understand them properly. Andrews Deller documents in detail where these unique rocks occur, highlighting the importance of laterites as a resource; the frightening hazards that they pose to people throughout laterite-mantled Africa, and their relevance to the history of erosion and intraplate deformation.

The central theme of Andrews Deller’s paper is the essential first step of mapping laterites and discriminating their facies. This rests on their mineralogical simplicity, and the unique and distinct spectral properties of those constituent minerals. The author matches these to the spectral coverage of freely available remote sensing data — Landsat TM, ASTER and ALI — each of which offers nuances to be exploited in uniquely discriminating the different laterite horizons. Rather than setting out to ‘unveil’ sophisticated new methods of computer analysis (to which few people in laterite-encrusted areas would have access), Andrews Deller explores the simplest, most revealing approaches to a previously overlooked challenge: laterite facies have never been discriminated and mapped before using remote sensing. The results in this well-illustrated paper are stunning, and any geologist (and probably many lay people) can understand what the figures show and the importance of mapping laterites, thanks to careful discussion. The result is a paper that combines interest, novelty and usefulness.

Write about your favourite fossil

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The success of the online encyclopaedia called Wikipedia stems from millions of people being able to write about their own expertise, and also to add to, revise, correct and update any entry. Building up a knowledge base that way is a lot faster and more agreeable than individual efforts. The authors of a useful website on fossils (www.palaeos.com), begun in 2002, recently ran out of steam. Rather than allow it to become fallow, they have turned it into a wiki (wiki wiki means quickly in the Hawaiian language) at www.palaeos.org. Hopefully it will grow explosively, and I have suggested to  Prof P.U. Siffli, of Sringeri University in Karnataka, India, that he should contribute his hitherto private but astonishing knowledge on fossil hamsters.

Gold rush

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As they say, ‘Gold is where you find it’ – gold mineralisation has a great diversity of settings. One of the oddest gold mines is the Ladolam deposit on the island of Lihir off Papua New Guinea — it is also one of the largest, with reserves of around 1300 tons (~41 million troy ounces). There, gold is being extracted from an open pit, cooled by water injection, in the crater of a geothermally active volcano. Aside from that it is one of many different kinds of hydrothermal deposit in which metals are transported and deposited by a plumbing system that delivers hot watery fluids. The hydrothermal system on Lihir is obviously still active, and it is possible to sample the fluid itself by drilling to depths up to a kilometre. Deep sampling is needed to obtain pristine fluids, uncontaminated by mixing with groundwater. Their chemical composition trns out to be surprising (Simmons, S.F. & Brown, K.L. 2006. Gold in magmatic hydrothermal solutions and the rapid formation of a giant ore deposit. Science, v. 314, p. 288-291).

The ground in which the deposit occurs is a breccia produced by explosive decompression when the volcano collapsed in its last magmatic throes, at about 400 ka. It is this brecciation that provided the intricate pathways in which gold was able to precipitate from the hydrothermal fluids. The samples have deuterium and oxygen isotopes that show that it is derived directly from magma. The fluid is extremely saline with very high chloride and sulfate ion concentrations. Around 50 kg of the fluid reaches the surface every second. Because it contains about 15 parts per billion of gold, it is possible to estimate how long it might have taken to produce the gold ore body: a surprisingly rapid 55 thousand years at the current rate of 24 kg of gold per year. Even more surprising is that the Lihir hydrothermal fluid is not particularly rich in gold compared with the fluids emerging from some active volcanoes. For instance Mount Etna is estimated to be delivering up to a tone of gold every year. However, before setting off on a gold rush to extinct volcanoes in the last hydrothermal phase, it is worth bearing in mind that forming a super-rich giant gold deposit requires that both gold transport and deposition are closely synchronised in a small volume of rock, otherwise the gold merely ends up in such a vast volume of rock that its extraction is not economic.

Long-term stability of the magnetic poles

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Back to about 200 Ma ago, charting the motions of plates is relatively simple using the striped patterns of magnetic field strength above the ocean floor, which reflect periodic reversals of polarity of the geomagnetic field. Post-Triassic plate motions can also be assessed in an absolute reference frame with the use of hot spot tracks. Since no ocean floor is older than 200 Ma, the method cannot be used before then. Instead, the inclination and direction of remanent magnetism in continental rocks, suitably corrected for any tilting by deformation, take on the role of tracking motions. The direction is taken as being towards the magnetic poles at the time a rock formed, whereas the inclination supposedly varies in a simple fashion with latitude as it does today; vertical at the poles and horizontal at the ancient Equator. The post-Triassic break-up of Pangaea allows the palaeomagnetic method to be tested, and for that period it holds up extremely well. The models that chart how continental masses separated from a late-Precambrian supercontinent, drifted and then clanged together in the Devonian to early Permian to form Pangaea use the assumption of a consistently dipolar magnetic field that was lined up with the Earth’s axis of rotation: about as uniformitarian as one can get. They are models that delight tectonicians and students alike. There is however, a period in Earth’s history, from about 750 to 600 Ma, when palaeomagnetic positioning gives worrying results. Evidence of glaciation occurs at nearly equatorial palaeolatitudes at least three times.

Taken at face value, these results form the basis for the ‘Snowball Earth’ hypothesis, and the 750 to 600 Ma period has been dubbed the Cryogenian. But there are two other ways of explaining what is about as far from uniformitarian as can be. Maybe there were long periods when the geomagnetic field was neither dipolar nor lined-up with the rotational axis, in which case palaeolatitudes for those periods would be totally meaningless. The other possibility, which is alarmingly odd, is that before about 600 Ma the angle between the Earth’s axis of rotation and the plane in which it orbits the Sun was not about 23.5°, but more than 58°. At a high obliquity, Earth’s rotation would then ensure that high latitudes were warmer than low ones, which would neatly explain away much of the evidence for ‘Snowball Earth’ conditions. It is a worrying idea, simply because some considerable force, i.e. a stupendous impact, would be needed to change the axial tilt from >58° to what it is now and probably has been throughout the Phanerozoic. Settling the matter once and for all seems now to have been achieved by David Evans of Yale University, using a simple yet ingenious approach (Evans, D.A.D 2006. Proterozoic low orbital obliquity and axial-dipolar geomagnetic field from evaporite palaeolatitudes. Nature, v. 444, p. 51-55).

Evans based his study on the uniformitarian assumption that conditions are just right for strong evaporation of shallow, enclosed seas between 15 to 35° of latitude either side of the Equator, which is where evaporite deposits are forming now. If true, and if the geomagnetic field has been much the same as it is now, except during reversals, then all evaporites should give palaeolatitude results with this narrow range. There are lots of them, going back to 2.3 Ga ago, and being quite soft it is easy to drill cores from them. Furthermore they contain wind-blown dust, the magnetic component of which would line up nicely with the geomagnetic field while salts crystallised. The results from 54 world-wide sample are quite a triumph, for no evaporite palaeolatitudes are further than 40° from the Equator, and their means fall within the modern latitude range of an excess of evaporation over precipitation. There are differences between different time periods – before Pangaea existed evaporites formed slightly closer to the Equator than in later times. The fact that they cluster also shows that the dominant component of the geomagnetic field has been consistently been a dipole. However, even though the fundamental assumptions on which palaeomagnetic measurements are based seem sound, there are still problems for the Snowball hypothesis. Are the magnetic measurements up to scratch and do the stratigraphic and radiometric ages of samples refer to the evidence for glaciation?

Bad news for lunar base

Whether or not the Moon becomes once again a target for exploration by astronauts, and for use as a launch pad for Mars, depend on whether there is any water there. There has been considerable optimism that perpetual shadows in some of the deep craters close to the south lunar pole might contain ice that has not been exposed to solar heating. There is a way of telling using radar imaging, and reconnaissance results from orbiting probes had suggested that ice was indeed there, hence the excited men in suits of various kinds. A check using far more revealing radar data produced using the Areceibo radio telescope – it has also produced images of Venus at far greater distances – show that both sunlit and shadowed areas on the Moon can give a signal that is theoretically that from ice (Campbell, D.B. et al. 2006. No evidence for thick deposits of ice at the lunar south pole. Nature, v. 443, p. 835-837). Since ice could never survive in full sunlight, the similar results cast great doubt on ice being anywhere else on the Moon. There also seems to be a correlation in degree of belief with degree of involvement with future lunar exploration preparation.