Magnetic polarity reversals

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The Earth’s magnetic field is changing all the time, in its intensity, direction and, now and again, its polarity.  It’s the last that proved the key to sea-floor spreading and plate tectonics, though ocean-floor magnetic “stripes”, and which has become a key stratigraphic tool for correlation and approximate dating.  Along with palaeomagnetic pole determinations, that are vital to continental reconstructions, the whole field still remains largely empirical.  Although widely agreed to be connected to changes in motions in the core, exactly what happens during reversals of geomagnetic polarity remains enigmatic, despite 40 years having passed since they were first recognised.  There is no doubt that they are quick events, but to judge their pace and what happens to field strength and direction during a “flip” requires high quality data that is well-calibrated to time.  Most early work focussed on magnetisation in igneous rocks, where the signal is strong.  Minerals such as igneous magnetite acquire a permanent magnetisation once they cool below their Curie temperature, but since accurate radiometric dating gives an age, not a range of ages, it might seem that all that is possible with lavas and intrusions is to obtain a series of points.  Fine for a time series, but useless for the details of reversals.  However, by modelling the cooling history of an igneous body, it is possible to calibrate different levels within it to time.  With careful choice, it has proved possible to find flows in flood basalt sequences that include the brief progress of a reversal.  The results seem very odd, the pole itself seeming to migrate rather than jump from north to south, and gross changes in intensity over a short time.  Improved instrumentation allows a shift from strongly magnetic basalts, to sediments that preserve much weaker signals.  These are due to the alignment with the field of magnetic grains as they slowly settle.  Marine sediment cores can now be magnetically characterised – the principle behind magneto-stratigraphy.  For geomagnetists the most recent reversals have proved especially instructive, when the sedimentary record is analysed (Clement, B.M. 2004.  Dependence of the duration of geomagnetic polarity reversals on site latitude.  Nature, v. 428, p. 637-640).  On average, the last four “flips” took about 7000 years to complete by migration of the magnetic poles.  Yet there is an oddity in the detail.  Sites at low latitude show significantly shorter periods (down to 2000 years) than those at high latitude (as much as 10000 years).  Clement’s explanation for the difference is the persistence of the lower intensity non-dipole field, which might suggest different core processes or a single process with several components that evolve at different rates.

Sulphur cycling and sea-level change

Sulphur is one the major prerequisites for life after carbon, hydrogen, oxygen and nitrogen, and the bulk of it is supplied by sulphate ions.  After chlorine, the SO42- ion is the most abundant anion in the oceans.  Not very much is added annually by river drainage, and although anaerobic bacteria remove some by reducing it to hydrogen sulphide so that it is removed from solution as a result of precipitation of insoluble iron sulphide, the sulphur cycle has been considered to be the most sluggish of all the major geochemical rhythms at the Earth’s surface.  Because iron sulphide is highly reactive in oxidising conditions, should marine sulphide-rich sediments become exposed at the surface their oxidation to sulphuric acid and iron hydroxide would rapidly add sulphate ions to seawater.  Studies of sulphur isotopes seem to suggest that this is not very important however.  Through sulphate-sulphide reducing bacteria, sulphur is implicated in the carbon cycle because of its sheer abundance, not so much from the encouragement and burial of the bacteria, but because they induce the highly reducing conditions that help a larger proportion of dead organic matter to remain unoxidised and become buried.  In a roundabout way, sulphur has a role in climate controls.  In fact, two roles.  Sulphate ions affect the alkalinity of seawater, and on that depends the oceans’ ability to dissolve CO­2 from the atmosphere.  The big question is, “Does the sulphate content of seawater ever change fast enough to have some impact on climate in the short term?”.  Most studies of the S-cycle have focused on sulphur isotopes, so a new twist is bound to be interesting.  Alexandra Turchyn and Daniel Schrag of Harvard University looked instead at the isotopes of oxygen within barium sulphate contained within seafloor sediments since the Late Miocene (about 10 Ma ago) (Turchyn, A.V. & Schrag, D.P. 2004.  Oxygen isotope constraints on the sulfur cycle over the past 10 million years.  Science, v. 303, p. 2004-2007).  Up until 6 Ma, the barite d18O (measured against mean ocean water values) stayed constant at about 9.5‰, and then rose to around 12.5‰ by 3.5 Ma.  Through the Late Pliocene and Pleistocene, the period of repeated glacial-interglacial cycles, it fell dramatically to its present level of 7.9‰.  In that later period, the average d16O of deep water foraminifera rose significantly.  The decline in “heavy” oxygen in marine sulphates can be linked to increased exposure of pyrite-bearing marine sediments during glacial sea-level falls when “light” atmospheric oxygen enters the sulphate ions that are produced.  Modelling suggests sulphate ions in seawater increased by as much as 20% during the Great Ice Age.  Whether that had an influence on the oceans’ take-up of carbon dioxide from the atmosphere in the last 3 Ma is yet to be evaluated.  However, Turchyn and Schrag’s detection of a short term shift in the sulphur cycle, and attributing it to falling sea level, may allow a new approach to global sea-level change, which has mainly been deduced from features in stratigraphy.

See also:  Derry, L.A. & Murray, R.W. 2004.  Continental margins and the sulfur cycle.  Science, v. 303, p. 1981-1982

Impacts’ effects

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Algorithms that model the physical effects of extraterrestrial impacts from the Lunar and Planetary Laboratory of the University of Arizona, headed by Jay Melosh, have been assembled into a handy on-line calculator, with notes on the processes involved.  If you want to find out if you will be fried, buried or blown to smithereens (probably all three if our luck is really out), and the chances of being harmed by alien lumps of rock or ice, you can find the calculator at http://www.lpl.arizona.edu/impacteffects/ .  It is not recommended for estate agents, because, unlike many other disastrous events, impacts can be anticipated anywhere.

Early humans of Beijing

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One of the most remarkable achievements of early humans (Homo ergaster aka H. erectus) was not their tools, but their migration out of Africa around 1.8 Ma, to reach as far as Indonesia and China.  There is no evidence for that feat having occurred again until fully modern humans arrived in east Asia about 70 ka ago.  The toolkit of Asian “Action Man” is unimpressive, in the sense that it resembles the slightly reshaped broken pebbles of the Oldowan culture, that first appears in the African archaeological record about 2.4 Ma ago.  Development in Africa of the enigmatic and beautiful bi-face or Acheulean axe was after the first Asians had departed, around 1.5 Ma.  So what were these early wanderers like; what did they want?  The decade-long work in China by Noel Boaz, an anatomist from the Ross School of Medicine in New Jersey and anthropologist Russell Ciochon of the University of Iowa will soon appear in their book Dragon Bone Hill, an Ice-Age Saga of Homo Erectus (Oxford University Press), which they preview in the 17 April 2004 issue of New Scientist (p. 32-35).  Boaz and Ciochon have worked mainly in Zhoukoudian near Beijing, a major resource for human remains whose different levels extend back to about 800 thousand years.  Another site in China, Longouppo, contains disputed remains as old as 1.8 Ma, as are Dubois’ famous discoveries of the type specimens of H. erectus by the Solo River in Java.  From the time when Zhoukoudian became famous among Chinese apothecaries as a source of “dragon’s bones” (a mixture of human and other animal remains) there has always been an air of myth about the findings there – a permanent dwelling for hundreds of thousand years, protected from glacial temperature falls by the consistent use of fire.  In essence, the publicised view is that “Peking Man” led a cosy hearthside existence for a very long time indeed.  Boaz and Ciochon tell a different, and more mundane story.  Most bones in  the deposit are those of a great variety of other animals, with disproportionately few of human origin, and those are highly fragmented.  The dominant species is a giant hyena, and many of the bones, including humans, are well gnawed, which is what hyenas do especially well.  There are occasional signs of human occupation and use of fire.  The human remains are encased in layered carbonate flowstone,.  Records of fluctuating d18O from that matrix, matched against the global time series of climate change, show that occupation was only during interglacials – the site was abandoned or unvisited during the depth of glacial periods.  Some animal bones show cut marks made by stone tools, and it is more likely that H. erectus raided to get remnants of other beasts’ kills, perhaps using fire, rather than being top of the predatory order.  The great surprise throughout Asia is the complete lack of development of stone tools from the primitive culture that arrived there, until as late as 20 to 30 thousand years ago, when Asian H. erectus vanished.  Apart from the stunning breakthrough to the bi-face axe, African erects also had a million-year long cultural stasis – resting on laurels with a vengeance.  Finally, from a number of skulls at Zhoukodian, Boaz and Ciochon have shown signs of trauma.  These are depression fractures, probably not necessarily fatal, but indicate sharp blows to the head with blunt instruments.  Their interpretation is that the Chinese erects settled disputes by bashing heads; so that aspect of culture has not changed a lot since.  Their story is not “politically correct”, but with publication of their book, other palaeoanthropologists can judge it on the basis of the evidence from Dragon Bone Hill.

Faster development of Neanderthals

Go to any horse sale and you will see bidders closely studying the teeth of their prospective purchases; the origin of the saying, “Never look a gift horse in the mouth”.  Teeth show growth ridges, and in grazing animals they are prominent, so that it is possible to judge the age of a horse easily and accurately.  Human teeth are different only in the less obvious signs of growth.  Microscopic examination reveals such records, down to the daily level, although the most prominent features are curious disturbances in their deposition that form approximately weekly.  They appear as ridges on the crowns of teeth.  The variable spacing of these perikymata provides a record of the pace at which adult teeth develop.  In modern humans the spacing becomes very much closer in the later growth history (towards the tooth’s cutting edge) than in its early stages, and reflects the slow development to full adult dentition.  In a painstaking study of hundreds of teeth from Cro Magnon and Neanderthal teeth, Fernando Rozzi of the University of Paris and José Bermudez de Castro of the Spanish National Museum of Natural Sciences have discovered an odd difference in the development rates of Neanderthals (Rozzi, F.V.R & Bermudez de Castro, J.M. 2004.  Surprisingly rapid growth in Neanderthals.  Nature, v. 428, p. 936-939).  The late perikymata of Neanderthals are more widely spaced than in Cro Magnon and modern humans, strongly suggesting that Neanderthals developed to adulthood by about the age of 15, three to five years earlier than us and our immediate ancestors.  As well as confirming that they are a separate species, the results suggest that Neanderthals, while acquiring brains as large, and in some cases even larger than ours, had evolved more rapid maturation and probably a genetically determined shorter adult life.  This would have had some effect on transfer of culture, which in human societies is often the most important value of elderly folk.   The fewer samples of teeth of earlier human species (H. heidelbergensis and H. antecessor) reveal an even greater surprise.  They are more like modern human teeth (albeit with signs of somewhat faster growth), which suggests that evolution of the Neanderthals involved a regression.  The authors suggest that the combination of a backward step to faster development with rapid brain growth to large size might reflect a very-high calorie diet together with adverse environmental conditions.

River incision and anticlines

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In many areas of active deformation, landforms that suggest that uplift and river down-cutting keep pace are very common.  Stream courses cross zones of uplift, rather than being diverted or ponded up to form lakes.  Traditionally, geomorphologists have described such drainages as “antecedent”, i.e. rivers that were present before uplift began.  They can be seen on all scales up to examples such as the Indus and Brahmaputra rivers that carve their way across the actively rising Himalaya.  The most common are anticlines through which streams flow in canyons perpendicular to the fold axes.  A curious and common feature is that the canyons are not haphazard, but often cut the fold where its amplitude is greatest and its axis plunges away from the site of incision.  The stupendous rates at which crustal rocks are eroded and transported away in the courses of the Indus and Brahmaputra, and in lesser drainages on the flanks of major extensional orogens, such as the Red Sea, clearly removes load from the crust.  Consequently there is an isostatic component to the uplift involved in the two cases at a grand scale.  Peter Molnar and Phillip England suggested an erosional role in large-scale uplift over a decade ago.  Intervening ridges rise higher than they would if erosion was slower or non-existent.  In major rift systems, the highest peaks are often within the escarpments rather than at the lip of uplift, sometimes more than 500 m higher.   Bearing this well-known process in mind, Guy Simpson of ETH Zurich, has sought evidence that it functions on much smaller scales (Simpson, G. 2004.  Role of river incision in enhancing deformation.  Geology, v. 32, p. 341-344).  That comes from the surprising symmetry of doubly plunging anticlines that are cut by rivers at their highest point.  His modelling suggests that the phenomenon can occur when the crust deforms plastically, allowing isostatic response to erosion on even minor scales during compression.  When deformation is by brittle means, any uplift of rigid crust is flexural and has long wavelengths, so that rivers bear no relation to local structures

Water on Mars; almost official

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Two lines of evidence from the current robotic explorations of Mars add to less tenuous ones that the planet is really wet – icy to be precise.  One is mineralogical.  Spectroscopy of the surface being slowly trundled across by a NASA rover, shows abundant signs of the hydrated, iron-potassium sulphate jarosite, which probably can only form under wet conditions.  When it was precipitated is not known with certainty, but it occurs in layered sediments that contain structures that clearly point to transport in and deposition from surface water.  The time when liquid water could exist at the surface probably goes back to the earliest events on Mars, tied to the famous canyons and more recently discovered dendritic drainage patterns.  The other evidence stems from even more remote sensing, that captures short-wavelength infrared radiation emitted by the Sun and reflected from the Martian surface.  Ices of water and carbon dioxide have distinct and unique reflected spectra, because of the different ways in which they absorb a small proportion of solar radiation.  Results from the OMEGA instrument aboard the European Space Agency’s Mars Express satellite show that the south polar region contains as much as 15% water ice mixed with solid CO2 (Bibring, J-P et al. 2004.  Perennial water ice identified in the south polar cap of Mars.  Nature, v. 428, p. 627-630).

Devonian broad-shouldered fish

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How, when and under what circumstances vertebrates got limbs to take them charging across the forested land of the late Palaeozoic form a central issue in our own evolution, as well as that of the other four-footed land animals.  By negative analogy with the functional though rather rudimentary enlarged fins of various modern fish that flop from pond to pond during dry seasons, many vertebrate palaeontologists have considered limbs as evolutionary adaptations in air-breathing fish once they made this a habit.  As so often, the fossil record has not given up enough evidence for that to be certain.  Well, an upper foreleg bone (humerus) has turned up in Late Devonian rocks from Pennsylvania at a time and in a context that strongly suggests it was carried by a fish (Shubin, N.H. et al. 2004.  The early evolution of the tetrapod humerus.  Science, v. 304, p. 90-93).  While not able to ride a bicycle, the advanced fish probably used what became limbs to hold itself motionless while lying in ambush for its prey.  That would provide a plausible point of departure from which walking might develop.

Early biomarkers in South African pillow lavas

It is now established that various kinds of bacteria infest rocks down to depths of 2 km or more, one particularly favourable habitat being in sea-floor basalts though which hydrothermal fluids travel.  Although the majority probably inhabits cracks and joints, some seem to work actively to corrode rock, especially volcanic glass, thereby obtaining mineral nutrients.  Signs of this microbial corrosion in modern volcanic glasses are radiating tubes on a scale of a few micrometres, that show up in micrographs, and many may have been overlooked by petrographers in all kinds of rock.  That they are definitely formed by organic activity is demonstrated by the presence of nucleic acids, carbon and nitrogen in the tubules.  Carbon isotopes from them show the strong depletion in 13C that is the hallmark of organic fractionation of natural carbon.  A team of geoscientists, from Norway, Canada and the USA, who have steadily accumulated evidence for biological rotting in modern oceanic basalts, turned their focus to the oldest, well- preserved pillow lavas in the 3.5 billion-year old Barberton greenstone belt of north-eastern South Africa (Furnes, H. et al. 2004.  Early life recorded in Archean pillow lavas.  Science, v. 304, p. 578-581).  Virtually identical microtubules seem common in them too, particularly in hydrated glasses that are now tinged with the low-grade metamorphic mineral chlorite.  Indeed, chlorite seems to have grown preferentially from clusters of the holes, which suggests that they formed before metamorphism of the basalts.  Micro-geochemical studies confirm the presence of hydrocarbons with low d13C.  The bulk of the tubules occur in the inter-pillow debris, that probably formed as glassy rinds as magma protruded on the Archaean sea floor.  As well as adding to evidence for ancient terrestrial life, the find has inevitably opened up the search for such signs in meteorites reckoned to have come from Mars.  In two, olivine grains show similar structures, although why the olivine hadn’t broken down in the presence of water that is essential for life makes such observations worth taking with a pinch of salt. A number of studies have stymied claims for early bacterial fossils (see Artificial Archaean “fossils” and Doubt cast on earliest bacterial fossils, April 2002 and December 2003 issues of EPN) and inorganic processes conceivably might create structures that can be mistaken for ones formed by biological action.  The Fischer- Tropsch  process is capable of producing hydrocarbons, and produces depletion in 13C abiogenically.  In the on-line April edition of Science Express (www.sciencexpress.org) experiments are reported that highlight the possible influence of chromium-bearing mineral catalysts in hydrothermal generation of hydrocarbons from inorganic carbon dioxide(Foustoukos, D.I. & Seyfried, W.E. 2004.  Hydrocarbons in hydrothermal vent fluids: the role of chrome-bearing catalysts.  Science Express, April 2004).  The Barberton greenstone belt is well known for ultramafic lavas rich in chromium, as are most early volcanic sequences.

See also:  Kerr, R.A. 2004.  New biomarker proposed for earliest life on Earth.  Science, v. 304, p. 503.

Australian surface not so old

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One of the most widely quoted bits of geological information that appear in non-specialist literature is that the oldest land surface on Earth is that of interior Australia.  Vast tracts are Precambrian capped by horizontal Permian glaciogenic rocks in places, but for the most part by relics of lateritic palaeosols that give it is famous red appearance.  The oldest outlying platform sediments are 1100 Ma old, so the actual surface does date back at least as far, but has it been exposed at the surface for that long?  Dating the present surface has not been easy.  New methods involving the creation of unstable isotopes by cosmic-ray bombardment offer a solution (see Measuring erosion rates, February 2002 issue of EPN), combined with apatite fission-track dating (Belton, D.X. et al. 2004. Quantitative resolution of the debate over antiquity of the central Australian landscape: implications for the tectonic and geomorphic stability of cratonic interiors.  Earth and Planetary Science Letters, v. 219, p. 21-34).  The results suggest that Australian landscape antiquity is a myth.  Erosion rates since the Cambrian varied over most of the Red Centre from 0.4 to 4.0 metres per million years, and reached as high as 17 m per Ma on occasion.  They suggest a common or garden history, comparable with those of most continental interiors.  Again and again it has been buried by sediments, albeit on a flat surface, and equally it has been exhumed several times by erosion.  Only at the outset of the Cenozoic did much of it sit unchanged for long, which enabled its red surface to develop.  The present surface is covered with what is termed regolith by Australians, but much of that is reworked material from the Palaeocene laterites that sits in a network of shallow drainage systems, including huge ephemeral lakes.  It might seem that recourse to Hutton’s “the present is the key to the past” should long ago have staved off the myth of the gnarled old place of which Australians have become inordinately proud.

Weak jaws allow bigger brains

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There is no topic in the geosciences that is more interdisciplinary than that of human origins.  Geologists, anthropologists (social as well as physical), archaeologists, geochemists, linguists, geneticists, dentists, specialists in nutrition and even novelists (for example Jean M. Auel) contribute.  Everyone is interested, and so everyone not only wants to have a say, but somehow to be involved.  Again and again in the pages, it becomes clear that bones and artefacts can no longer make major breaks through.  The Out of Africa hypothesis, although suggested by Charles Darwin and many palaeoanthropologists since, became widely accepted (though not completely) after the evidence for relatedness emerged from comparisons of mitochondrial DNA from women throughout the world.  That showed clear signs of a last common ancestor for all human groups around 200 thousand years ago, to whom modern Africans were most related.  At the end of March 2004 geneticists have again come up with something startling, but this time not guessed at before.

The first beings to whom the generic name Homo seems appropriate appear in the hominid fossil record about 2.0 million years ago.  Apart from evidence for bipedality and their association with rudimentary, but nonetheless deliberately made stone tools, the earliest humans are marked by the fragility and roundness of their skulls.  Many specialists have argued that “gracile” crania are an evolutionary pre-requisite for the growth of brain capacity – they can expand for a long period during development, before becoming completely ossified in adulthood.  The predecessors of these early humans (australopithecines) and their close companions in the African savannahs (paranthropoids) had smaller brain capacity and also very bony heads.  In the case of the paranthropoids, undoubtedly as closely related to earlier hominids as the first tool-making humans were, they survived as a group for another million years but never expanded their brains, nor presumably their intellects.  Bone-headed hominids had one feature in common with all earlier apes, and with the genera that survive today; powerful jaws and muscles that drive them.  To some degree or other they all have crests on top of their skulls, which provide the seats for these big jaw muscles.  Wielding awesome biting power requires skull strength, and therefore bulky bone.  That encumbers any possibility for expansion of the internal brain cavity, and also drives their bearing species into tight feeding habits.

A team of geneticists, anatomists, developmental biologists and plastic surgeons from the University of Pennsylvania and the Children’s’ Hospital of Philadelphia have studied one gene sequence of several that encode for a type of protein (myosin heavy chain) associated with the powerhouse muscles that are attached directly to bone, such as those which drive jaws (Stedman, H.H. and 9 others 2004.  Myosin gene mutation correlates with anatomical changes in the human lineage.  Nature, v. 428, p. 415-418).  Their investigation began with an interest in muscular dystrophy and possible underlying factors.  Specifically, the most interesting gene (MYH16) is expressed in primate jaw muscles.  The human gene contains a mutation that prevents the accumulation of the protein in our jaw muscles, so they cannot be as strong as those of other primates and mammals in general, in which the gene functions as it should.  By analysing MYH16 and related gene sequences in humans from widely separated populations, the researchers showed that the mutation in MYH16 diverged earlier than those in other MYH-related genes.  To estimate the time of that divergence involved detailed analysis of the mutations in other living species – dogs, macaque monkeys, oran-utans and chimpanzees.  This showed that MYH16 evolved under Darwinian selection, conferring fitness advantage, in the ancestral lineages leading to each species, whereas in humans there was no selective constraint.  Under the second condition, it can be assumed that any evolutionarily neutral changes took place at a constant rate.  Calculations suggest that in the human lineage, the mutation appeared 2.4±0.3 Ma ago.  That coincides with the earliest appearance of tools and a little earlier than the first remains of early Homo fossils.  The conclusion could be one of several: lost of biting power created conditions for expansion of a lighter skull; a changed diet to include more meat reduced the need for strong jaws, so that the mutation did not have a deleterious effect; or hands freed by walking upright did a lot of the work that other primates can only accomplish with their mouths.  Whichever, once established without decreasing fitness, the road to enlarged brains and fuller consciousness was opened by a chance event.

See also:  Ananthaswami, A. 2004.  less bite, more brain.  New Scientist, 27 March 2004, p. 7;  Currie, P. 2004.  Muscling in on hominid evolution.  Nature, v. 428, p. 373-374

Dental records of earliest hominids

Conditions on land are not as conducive to preservation of fossil remains as those on the sea floor.  When an animal dies it is generally eaten, what is left rots and is gnawed, and the action of wind and water breaks up the skeleton and transports it, and only this debris is preserved if it is buried by sediment.  The best chance of preservation is if the animal falls in a lake or bog, or in the case of fully modern humans if it is deliberately buried.  The so-called Turkana Boy (H. erectus) is an almost complete skeleton, because he did end up, uneaten, in a swamp.  Sturdy, large animals and those small and light enough to be quickly washed to burial stand the best chance of appearing as complete fossils.  Primates are medium-sized and lightweight, and that presents palaeoanthropologists with their single biggest problem, incompleteness of most fossils that they find.  In the depths of the Afar Depression of Ethiopia and Eritrea, which is the most productive area for hominid specialists, conditions from the early Miocene were not the best for preservation.  While the depression developed by extensional tectonics, its flanks rose to form the mighty Ethiopian escarpment from which torrents flowed seasonally.  High-energy streams clearly will break up any articulated skeleton and batter what is left before they end up in gravels and sands on the floor of the depression.  So it is a credit to the patience, experience and sheer visual acuity of those who work there that they can piece together the earliest parts of the human story.  Yohannes Haile-Selassie, Gen Suwa and Tim White have pushed back and detailed our record further than any other group, thanks in part to the richness of the Miocene to Recent Middle Awash sedimentary and volcanic sequence with which they work.  In 2001 Haile-Selassie discovered the earliest Afar hominid so far (see Taking stock of hominid evolution, March 2002 issue of EPN), Ardepithecus ramidus kadabba dated between 5.2 and 5.8 Ma.  In age it roughly matches Sahelanthropus and Orrorin from Chad and Kenya.  Only a leg bone from Orrorin gives some indication that it was bipedal, but all show cranial features that mark them out as probable hominids.  Of all the body parts of any animal, the teeth are the most likely to survive with little change.  Because our closest living relative are chimps, comparing early teeth with theirs, as well as with those of later hominids, is about the best that can be done to seek relatedness.  The three notable workers on Awash hominds have now reported their results (Haile-Selassie, J. et al. 2004.  Late Miocene teeth from Middle Awash, Ethiopia, and early hominid dental evolution.  Science, v. 303, p. 1503-1505), which suggest the earlier find is a distinct species A. kadabba.  Putting together upper and lower canines and adjacent premolars shows a close resemblance to those of modern chimps.  However, it requires detailed measurements of the tooth shapes to check if the resemblance is more than superficial, and it is not.  All extinct and modern apes show signs of automatic honing of their canines, whereas hominids do not.  Not only A. kadabba but Orrorin and Sahelanthropus too, show no sign of canine honing.  That points to early members of human evolution.  Yet, the three show such close similarity that it is hard to support the idea that they are from anatomically different genera, despite their occurrence thousands of kilometres apart.  It is that close resemblance (and in other features as well) that re-opens the long debate between a complex, messy “bush” of human descent made up of many contemporary, different creatures, and one of a single line of descent.  Dental features are not enough to decide between the two.

New take on end-Palaeocene warming

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Six years ago vast areas of Indonesia caught fire after an unusually dry phase in the El Niño – Southern Oscillation (ENSO).  Burning forest and peat deposits swathed a vast area in smoke, but another alarming aspect was the greatest addition of carbon dioxide to the atmosphere in half a century.  Such a wildfire on a global scale is thought to have marked the end of the Mesozoic, perhaps triggered by the K-T impact event and encouraged by higher oxygen content in the atmosphere.  Present oxygen levels seem to be at a balance that staves off spontaneous combustion of green vegetation, but only a few percent more would render vegetation much more prone to bursting into flame.  The end of the Palaeocene involved a sudden global warming that coincides with a decrease in the proportion of 13C in marine carbonates.  Since photoynthesis, at the base of the trophic pyramid, favours light 12C, such a negative d13C “spike” is generally ascribed to an unusually high release of organic carbon to the environment.  The end-Palaeocene warming may have resulted from a massive release of methane from gas-hydrate buried in shallow seafloor sediments (See Methane hydrate – more evidence for the ‘greenhouse’ time bomb and Plankton and the end of the Palaeocene-Eocene global warming August and October 2000 issues of EPN).  However, massive burning of living biomass could also produce the carbon-isotope signal.   Telling the two mechanisms apart requires information from other organic-related cycles.  One key is comparing the carbon- and sulphur-isotopic records that enables the place in which carbon had been stored geologically.  For marine burial, the effect of aerobic bacteria that completely oxidises hydrocarbons back to carbon dioxide and water needs to have been suppressed.  Periods of massive marine carbon burial coincide with oceanic anoxia episodes, when anaerobic bacteria beneath the seafloor reduce dissolved sulphate ions to sulphides, thereby depositing lots of iron sulphide (pyrite) in black organic mudrocks.  This sequesters sulphur that is depleted in 32S into marine sediments, so that the marine carbon- and sulphur-isotope records fluctuate in a clearly related way.  During the Palaeocene this relationship is absent, while overall the carbon isotopes do signify progressive burial of organic carbon.  The decoupling of the two cycles points to carbon burial on the continents, forming peat and eventually coal deposits.

Playing games on Snowball Earth

For as long as anyone can remember there has been a parade of geoscientific bandwagons in town.  Three of the floats today carry banners saying, “Snowball Earth”, “Climate models” and “continental erosion and CO2 drawdown”.  Of course there is serious science aboard each, but they are getting overcrowded, especially as separate bands try to jump from one to another.  When it sometimes seems, as now, that the “next Big Thing” is some way off, we get the unseemly spectacle of some bands trying to straddle two or even several of the wagons.  Three is quite a feat, yet the 18 March 2004 issue of Nature contains perhaps not a vast human pyramid, but at least a tetrahedron of the genre (Donnadieu, Y. et al. 2004.  A “snowball Earth” climate triggered by continental break-up through change in runoff.  Nature, v. 428, p. 303-306).  From about 1100 to 750 Ma ago, the bulk of continental lithosphere was gathered in a supercontinent known as Rodinia (from the Russian for “Mother Earth”).  By analogy with modern Eurasia, and the stratigraphic record from the Phanerozoic Pangaea supercontinent, the centre of Rodinia would almost certainly have been dry, being so far from the ocean.  Break-up of that continental mass would also probably have allowed moist maritime air to penetrate over a larger proportion of the fragments.  The hypothesis that Donnadieu and colleagues try to test using linked geochemical and climate models is that such a tectonic change would increase continental weathering and reduce the “greenhouse” effect.  The weak acid formed by solution of carbon dioxide in rain water can provide hydrogen ions to break down silicate minerals.  The reactions contribute bicarbonate and soluble metal ions to surface and subsurface water.  Ultimately, both reach the oceans and contribute to its chemistry.  If conditions are suitable, calcium ions in particular combine with bicarbonate to precipitate calcium carbonate on the ocean floor, either through the action of organisms or inorganically.  The two chemical equilibria involved result in a net burial of one carbon atom out of the two involved in the weathering, thereby drawing down carbon dioxide from the atmosphere.  The climate model used in their cyber-experiment resolves the Neoproterozoic Earth into cells that are 10 x 10 degrees (about 100 thousand km2) and considers Rodinia at 800 Ma and the result of its break-up at 750 Ma, the time of the first good evidence for extensive low-latitude glaciation.  The results, after some tinkering, suggest that increased continental weathering could have reduced CO2 levels to 250 parts per million.  Taking account of a 6% less energetic Sun at the time, this would have produced sufficient cooling for ice caps to exist to sea level at the equator.  So, taken at face value, the hypothesis seems plausible.  However, there are major snags.  First, in a mere 50 million years their model sees continental dispersion on a scale that has not yet happened to Pangaea in about 200 Ma of Phanerozoic time.  Second, since continental area remains constant, the proportion of rainfall, and therefore weathering and runoff, involving continental crust also stays fixed.  Third, continental weathering refers to the crystalline part of its crust, in which there are unstable minerals, such as feldspars, that can do the chemical trick.  We have little idea how much of the continents at that time was veneered by sediments that are the products of earlier chemical weathering, and contribute nothing to the process.  Exposing such deep crust depends to a large extent on mountain building, which continental extension does not encourage.  Fourth, carbon dioxide is not the only source of hydrogen ions that are involved in weathering, especially as much of it goes on in groundwater – bacterial action and oxidation of iron sulphides create much more acid conditions that rainwater.  Fifth, and most important, where is the complementary geochemical evidence?  Feldspars of the continental crust, on which the hypothesis mainly rests, have high contents of rubidium compared with their oceanic counterparts, and they are old.  Much of Rodinia was underpinned by crust formed as far back as 4 billion years ago.  Prolonged decay of 87Rb to radiogenic 87Sr makes the strontium isotopes of continental material very different from those of the ocean floor – it has a much higher 87Sr/86Sr ratio.  Since soluble strontium would be released to runoff by continental weathering, that signature makes its way to the ocean and should pop up in marine carbonates.  Although the ocean strontium isotopes in the Neoproterozoic did rise a little, it did not peak until the very end.  In fact, the details show that the periods around supposed “snowball” conditions involved downturns in radiogenic strontium supply to the oceans.  Whatever the model suggests, all that it amounts to is the equivalent of a table-top train set

Could ice sheets have existed in the Cretaceous?

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Finds of Late Cretaceous dinosaur remains and substantial coal deposits at near-polar latitudes in both hemispheres seemed to confirm that the end of the Mesozoic experienced hothouse conditions.  Even so, both are very odd because of the darkness of polar winters; how could plants photosynthesise and supposedly cold-blooded reptiles stay warm?  To add to these oddities, it has now been suggested that periodically there were Antarctic ice sheets substantial enough to draw down sea-level (Miller, K.G. et al. 2004. Upper Cretaceous sequences and sea-level history, New Jersey Coastal Plain.  Geological Society of America Bulletin, v. 116, p. 368-393).  The possibility comes from a detailed stratigraphic and palaeontological analysis of Late Cretaceous sequences on and off the eastern seaboard of the US.  There are 11 to 14 sequences that show shallowing-upwards changes in the near-shore environment, somewhat similar to the cyclicity of Carboniferous times.  Calibrating the section with strontium isotopes and fossil changes suggests that sea-level ups and downs greater than 25 metres occurred swiftly (much less than 1 Ma).  This is considerably faster than changes due to variations in the volume of the ocean basins that result from fluctuations in sea-floor spreading rates, but if localised in eastern North America might have resulted from local tectonics, such as episodic deepening related to extensional tectonics.  The surprise is that the changes correlate well with those in western Europe and on the stable Russian platform, pointing to global, eustatic changes in sea level.  There is some correlation with oxygen-isotope records from foraminifera, so there is a strong possibility of a glacial cause.  The degree of fluctuation matches the effect on sea level of ice volumes of the order of 106 to 107 km3.  This is considerably more than the volume of the present Greenland ice cap, but on Antarctica it would have occupied only a small part of the surface.  There is another alternative; that eustatic changes are not well understood and there is a bias because of the Pleistocene correspondence between them and changes in continental Arctic ice sheets.  The amplitudes of the three different records do not match well, although their timing does.

Biology and iron minerals

The principal colouring agents in rocks, especially those of sedimentary origin, are iron minerals, foremost of which are oxides and hydroxides (e.g. hematite and goethite).  It doesn’t take much of either in a sedimentary grain coating to impart the vivid colour variations seen in some sedimentary formations.  It is easy to suppose that such veneers formed while the sediments were at the surface in an unconsolidated state, but there is much evidence that at least some, if not all, formed in buried sediments saturated with groundwater.  But the problem is getting the iron into pore spaces as well as precipitating its oxides and hydroxides.  Iron in its divalent state (Fe-2) is soluble, but exists only under reducing conditions, so it does not easily enter surface waters that supply groundwater.  In its trivalent state (Fe-3) iron is highly insoluble, and that is how it occurs in oxides and hydroxides.  Yet groundwater tends to lose its oxidising potential because dissolved oxygen is consumed by aerobic bacteria, and oxidation is required to convert soluble Fe-2 to insoluble Fe-3, so that hematite and goethite skins can form around sediment grains.  A clue to the precipitation method comes from a study of slime-encrusted surfaces in old mine workings (Chan, C.S. et al. 2004.  Microbial polysaccharides template assembly of nanocrystal fibers.  Science, v. 303, p. 1656-1658).  Although oriented towards the possibility of bacteria creating materials useful in nanotechnology, this non-geological paper might ring a few bells.  It shows how filaments (of the order of a few nm) that make up bacterial slime are associated with similarly thin and long filaments of one of the precursors to goethite.  The bacteria involved use the oxidation (electron removal) of Fe-2 to Fe-3 as a source of metabolic energy.  They colonise highly reducing waters, so there is a ready source of dissolved Fe-2 for them to exploit, especially in old mine workings, but also in groundwater cut off from the air  There is a snag for the bacteria, because Fe-3 is highly insoluble and could easily snuff out processes in the cells and cause their death.  So in evolving this chemo-autotrophic metabolism they would also have to evolve a means of disposing of its by-product.  The filaments are chains of polysaccharides grown outside the cell wall that act as templates for the precipitation of Fe-3 minerals.  The techniques used to show this include very-high resolution electron microscopy.  It would be interesting to see if very high resolution images of iron-stained mineral grains reveal  relics of these intricate structures.  Less powerful methods have already shown tiny spheres of magnetite in sediments above petroleum fields that formed biogenically through another metabolic process.

How old is the Dalradian?

Half the Scottish Highlands, from the Great Glen to the Highland Boundary Fault, and their equivalent in Ireland, is occupied by a convoluted orogen that is dominated by an almost exclusively sedimentary sequence of Neoproterozoic age – the Dalradian Supergroup.  Its importance is historical, for this is where many of the fundamental tenets used in unravelling complex terrains were developed and tested.  This still goes on, building on over a century of research in an easily accessible area.  Briefly, the Dalradian orogen evolved from a series of extensional basins, in a shelf area, that imposed considerable variations in thickness of the Dalradian sequence.  Protracted deformation in the Late Cambrian to Early Ordovician developed the structural complexity of the orogen, partly controlled by the original variations in sedimentary thicknesses.  We know the youngest age of the Dalradian, because its upper parts contain Cambrian fossils, estimated to be about 509 Ma old.  The earliest age for sedimentation has so far only been guessed, and must be younger than the 800 Ma of migmatites on which its lowest members rest .  The problem is that only one series of dateable volcanic rocks occur in the pile, and they are towards the top (601 Ma old).  At most the whole sedimentary sequence spans 300 Ma, and that in itself is most peculiar.  Most geologists have assumed continuous sedimentation under a great range of environments, but only because they have never found evidence for erosion in the sequence; hardly surprising from the complexity, and not-so-good exposure.  Yet nowhere on the planet is there a sedimentary sequence spanning such a time period that does not contain several unconformities; things have never been that quiet for so long.  Probably the only feasible way to get a handle on the duration of the Dalradian sedimentation is by matching geochemistry of the numerous marine limestones in the sequence with the global record for the Neoproterozoic, that is by seeking signs of the secular variations in the composition of seawater during that Era.  Scottish geoscientists have applied that technique, using 47 samples of Dalradian limestones (Thomas, C.W. et al. 2004. 87Sr/86Sr chemostratigraphy of Neoproterozoic Dalradian limestones of Scotland and Ireland: constraints on depositional ages and time scales.  Journal of the Geological Society of London, v. 161, p. 229-242).  Unsurprisingly, the results do not show a smooth curve that can be matched directly with various estimates of secular change in seawater strontium isotopes; the limestones occur haphazardly through the sequence.  The effort is not helped by considerable differences between global seawater strontium isotope curves compiled by several authors, so Thomas and colleagues’ interpretation is limited.  Yes, the Dalradian is younger than 800 Ma, but by how much cannot be said with confidence.  Its base is an unconformity that represents erosion of an older 800 Ma orogen, and how long that took is anyone’s guess.  The lowest Dalradian limestone falls in a strontium-isotope span that matches that for about 700 Ma, which fits with recent evidence for continued thermal activity in the underlying complex at 730 Ma.  Around the middle of the Dalradian deposition there occurs one of the most spectacular examples of possible glaciogenic rocks in the Precambrian, the Port Askaig Formation, which has been widely regarded as a product of one of the “Snowball” Earth events of the late Precambrian.  If the Dalradian deposition did begin around 700 Ma, then this unit cannot have formed in the earliest and best documented Sturtian glacial episode at 730 Ma, but perhaps in the younger Marinoan-Varangerian one (640 to 560 Ma).  The paper concludes with the time-honoured phrase “…await the application of alternative dating techniques”.   It may be a long wait, and perhaps the most important unresolved aspects of the Dalradian are whether or not its 30 km maximum thickness represents several distinct depositional basins, and if it contains numerous breaks in deposition.

A “Whoops” moment for geochemists?

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A great deal of effort and innumerable theses and papers have gone into modelling the derivation of magmas from their parent rocks, especially the mantle, over the last three decades.  Most is based on the division of trace elements into “compatible” and “incompatible”, the first being those which tend to remain in minerals that make up the residuum during magmagenesis, and the second those that favour melts.  Most incompatible elements have large ionic radii. The modelling centres on the degree to which elements remain in solids, the appropriate parameter being an element’s mineral-melt partition coefficient (KD).  Partition coefficients are usually deduced from an element’s abundance in phenocrysts that are in contact (and supposed equilibrium) with an igneous rock’s groundmass material, which is assumed to have formed from magma, and its concentration in that once liquid phase.  Models for partial melting and fractional crystallisation, plus several variants, all involve KDs, for olivines, pyroxenes, feldspars, garnet, amphiboles and so on.  For the generation of basaltic magmas, the first step is partial melting in the mantle itself, for which direct estimation of KDs is not possible.  Instead they are assumed from mineral-melt chemistries in crustal igneous rocks, with some allowance for elevated temperatures and pressures and other conditions.  Each mineral has its own distinctive suite of KDs for many elements, and the chemistry of an igneous rock has often been traced back to which suite of minerals was present in a residue, i.e. the source rock itself, as well as the degree to which one or other process proceeded.  The 19 February 2004 issue of Nature included an ominous article (Hiraga, T, et al. 2004.  Grain boundaries as reservoirs of incompatible elements in the Earth’s mantle.  Nature, v. 427, p. 699-703). 

The study by geochemists at the University of Minnesota and Oak Ridge National Laboratory, USA, concentrated only on the mineral olivine, and a few elements present at trace levels in it.  Their experiments simulated equilibrium conditions under mantle conditions.  Results showed that incompatible elements in olivine, such as Ca and Al, tend to concentrate mainly at boundaries between grains where they are readily available to any melt that starts to form, rather than uniformly throughout the mineral grain.  The finer the grain size of the rock, the greater the area of grain boundaries, and so the more incompatible elements tend to be concentrated at them  The tendency is predictable on thermodynamic grounds, but has only been studied previously in alloys and other artificial materials.  Geochemists have generally regarded grain boundaries as places where impurities in rocks gather.  If the same rock is analysed with and without the crushed powder having been washed in acid, different trace element concentrations result.  This has been attributed to secondary effects, such as the passage of hydrothermal fluids or groundwater.  Since KDs that are used widely involve concentrations in whole mineral grains, the basis of geochemical modelling might be compromised.  Melting begins at grain boundaries, so the low degrees involved in generating basalts could be biased by the effect.  Moreover, vapour phases moving through the mantle (supercritical water and CO2), will follow grain boundaries too, and so may easily pick up and transport incompatible elements.  Their entry into the crust carrying mantle-derived incompatible elements, such as rare-earths, strontium and lead, would lead to metasomatic effects that could play havoc with interpretations of isotopic data based on these elements.  Carbonatites, probably formed from mantle-derived carbonic fluids, are enriched in many incompatible elements.  Similarly worrying data, such as estimates of the incompatible element partitioning into carbonic fluids, have emerged in the past, but so far have been notable only for the silence with which most geochemists greeted them.

The creators of worlds

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Inverting Robert Oppenheimer’s memory of the line in the Bhagavad Gita, “I am become Death, the destroyers of worlds”, during his Road-to-Damascus moment when the first atomic weapon was tested, may seem an odd headline for an article on geochemistry.  But geochemists sometimes do give the air of being on the verge of solving the “Big Question”.  Alex Halliday of ETH in Zurich is one of them (Halliday, A.N. 2004,  Mixing, volatile loss and compositional change during impact-driven accretion of the Earth.  Nature, v. 427, p. 505-509). It is now well accepted that Earth’s early evolution was one of repeated big impacts during planetary accretion.  It probably culminated in a collision with a Mars-sized planet that not only created the Moon from the debris splattered from both bodies, but set the Earth’s chemistry for all subsequent time; a sort of geochemists’ Year Zero.  When that happened and what ensued has all manner of connotations (see Geoscience consensus challenged in EPN for January 2004).  Halliday reviews evidence from several isotopic systems (Pb, Xe, Sr, W) that are reckoned to be appropriate “fingerprints” for the environments in which planets accreted.  His treatment takes the data as a whole, rather than separated into one or another isotopic system. He begins with the assumption in most accretion models that metallic cores form continuously and in equilibrium with the silicate outer mantle of rocky planets.  That is important in using W isotopes to model the “when”, since tungsten is likely to enter iron-rich metal rather than silicates (see Mantle and core do not mix in EPN February 2004).  In fact estimates for the time taken for the Earth to gather 2/3 of its mass based on W isotopes (~11 Ma) are a lot faster than those based on other isotopes (between 15 to 40Ma).  Halliday’s explanation is the seemingly sound one that when big things form from smaller ones (whatever contributed to core and mantle), the chances of them mixing and reaching equilibrium, before they definitively separate into the inner and outer Earth, are not good.  Reviewing the somewhat bewildering permissiveness of isotopic data from Earth and Moon that bear on “Year Zero” he concludes that the massive loss of xenon (and other “volatile” elements) that characterises Earth, by comparison with what is known about the Solar System’s pre-planetary composition, was 50 to 80 Ma after the “start of the Solar System”.  The Moon has provided insufficient data for its age of formation to be tied down isotopically.  Although its Hf-W age might be >44 Ma relative to the Earth’s beginning, there again, perhaps >54 Ma, and it may have formed even later.  Eventually we reach modelling (read “speculation”?) that takes us to the putative composition of the culprit for Year Zero, “Theia” (a Titan and the product of incestuous liaison between Uranus and his mother Gaia).

What seems odd to me is that some of the parent isotopes for those used in fingerprinting (e.g. 182Hf for 182W, and plutonium for a Xe isotope) can only form in supernovae events, and are so short-lived that the balance between their formation and their influence on partitioning of their daughters in planets is pretty delicate in terms of timing.  Indeed all radioactive isotopes, and every element with greater atomic mass than iron, in the Solar System have this origin, because it is impossible for a star the size of the Sun to form them.  Massive stars that become supernovas are common enough, and when they “go off” and what blend of heavy elements they produce depend on how big they were and when they formed.  Interstellar material is surely a mix of debris from a number of such events of different ages, and new stars and planetary systems form from that.  Maybe they are triggered by nearby supernovas, but that also contributes to the isotopic mix that has evolved since a galaxy formed.  Just suppose that the mix for the Solar System was heterogeneous, with differently aged uranium, thorium, rubidium, hafnium and other elements heavier than can be formed inside small stars like the Sun, and must have formed in big ones that eventually blasted their products into interstellar space.  If the Earth accreted as an open, non-equilibrated system, then what of the Solar System itself?  Bit early to say, really….

Kennewick Man may not be re-interred

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Seven and a half years after the discovery of a 9300-year old human skeleton in Columbia River alluvium in Washington state, USA, researchers may finally be able to study the remains.  So-called Kennewick Man caused a storm when first unearthed, for his skull was very different from that of any other early American colonist.  Indeed, partial studies suggested close resemblance to Europeans.  Four Native American tribes in the Pacific Northwest claimed the skeleton for reburial, under the Native American Graves Protection and Repatriation Act.  The move was not entirely connected with respect for sacred rites.  Evidence that the area might have been first colonised by people who were not related to the tribes living there just before European occupation in the 19th century could undermine claims for mineral and other land rights by native people.  On 4 February 2004 a San Francisco court ruled that the remains were so different from any North American indigenous people, that the claimants had no rights over them.  Studies of a skull cast of Kennewick Man since he was placed under lock and key now suggest a possible origin from Asian hunter-gatherers similar to the Ainu people of modern Japan.  However, modern techniques of genetic analysis and isotopic studies of tooth enamel that could settle the issue of origin and relatedness require the original material.  Interestingly, a spear point is lodged in the pelvis, so, like the famous Ice Man of the Italian-Austrian Alps, Kennewick Man may have been the victim of either a deadly dispute or ritual killing.

Onshore gas hydrate reserves close to recovery

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The Mackenzie delta in Arctic Canada has been an area of conventional hydrocarbon exploration for decades.  In 1972 methane-ice mixtures in the permanently frozen ground were discovered in one well at a depth of about a kilometre during exploratory drilling.  They are rich, with up to 90% of the pore spaces in alluvial gravels being full of the white gas hydrate.  Being associated with conventional gas at greater depths, there is a good chance that combined production could make the considerable reserves economic.  On their own, gas hydrates are not yet economic, even onshore, since they would need heating to break down the peculiar compound, and natural gas prices are currently at a low level.  Economics also depend on a conventional gas pipeline being extended to the area  Tests and computer simulations suggest that production of deeper conventional gas can lower the pressure on the gas hydrate inducing it to break down and add to the flow from a well.  In maybe 10 to 20 years production could begin.  The likely origin of the Canadian reserves and those in the North Slope of Alaska is from methane leaking from deeper reserves to “freeze” in the colder conditions at shallow depths.

Arctic North America could eventually produce up to one sixth of current US natural gas consumption from onshore gas hydrate.  Of course, vastly greater gas-hydrate potential exists offshore – between 10 000 to 42 000 trillion cubic metres (tcm) world-wide, compared with 370 tcm of estimated conventional gas reserves.  Methane (CH4) burns to produce less carbon dioxide per unit of heat energy than more carbonic natural gas, so is a means of easing “greenhouse” gas emissions.  Potentially it could be feedstock for CO2-free hydrogen production.  Pressures on the economy of Japan, which has very few natural energy resources, have prompted Japanese researchers to begin exploratory offshore drilling into the Nankai trough offshore of SE Japan, where there are potentially rich reserves of gas hydrate in sands.  This may produce commercially in 10 to 15 years.  The thorniest problem with many gas hydrate deposits is that they are in “tight”, fine-grained sediments.

Source:  Kerr, R.A. 2004.  Gas hydrate resource: smaller but sooner.  Science, v. 303, p. 946-947

Quantifying motions inside continents

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If you are a member of the Geological Society of America you will either have heard or read the 2003 Address of its President (Burchfiel, B.C. 2004.  New technology; new geological challenges.  GSA Today, v. 14, p. 4-10).  If not, get the February 2004 issue of GSA Today, if only for the wonderful illustrations in Burchfiel’s paper.  His topic is how the use of ever-increasing precision of satellite global positioning (GPS) has revolutionised continental neotectonics, since it began to be used by geoscientists in the late-1980s.  The illustrations have a backdrop of what I suspect to be the 90m resolution Shuttle Radar Topography Mission (SRTM) digital elevation model (DEM), and show the fine topographic detail that stems very much from active tectonic movements.  Superimposed on them are estimates of the speed at which points on the surface are moving and the directions of motion, gathered using GPS technology.  Measured in mm per year, these velocities stem from the most precise positional measurements, with the degradation built into the GPS satellite signals for US military reasons (turned off in 2001) removed using differential processing.  They are averages representing motions over the last 17 years or so.  The most dramatic example covers the Tibetan Plateau and areas to the east of it, based on extensive work by Chinese scientists..  In general it shows a sort of clockwise swirling away of expelled crust east of the Eastern Himalayan Syntaxis (the “big bend” at the eastern termination of the Himalaya) in the ranges through which the headwaters of the Irrawaddy, Salween and Mekong rivers flow, rather than the eastward expulsion towards the China Sea first postulated by Tapponier in the early 1980s.  Field studies suggest that this kind of motion has been going on for at least the last 4-6 Ma.  Another conflict with expectation lies in the area of the Longmen Shan mountains and the huge Sichuan Basin of western China.  A simple model of crust being expelled from the zone of the India-Asia collision suggests that Tibetan crust would be moving eastwards here to throw up the steep front of the Longmen Shan above the Sichuan Basin.  There is in fact very little sideways movement at the surface.  Explaining this requires deep crust from Tibet moving in a ductile manner far below, thereby “inflating” the Longmen Shan where entirely different kinds of crust are juxtaposed..  Many of the motions in East Asia can only be explained in terms of differential movements at different levels in the lithosphere, and the influence of subduction systems, such as the Indo-Burman and West Pacific, as well as the long-suspected expulsion of over-thickened crust in Tibet due to increased gravitational potential there.

Remote sensers now employable

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A research area could be said to have come of age when those who have participated find that they can get a job.  Gone are the days when vast experience in field mapping, skills with mass spectrometers and even encyclopaedic knowledge of tiny fossil remains ensured more than a cursory reading of your CV by potential employers.  In the 32 years since the first availability of Landsat data there has been a big shift in the employment prospects of young geoscientists.  The dominant trend has been into the broad field of environmental geology.  A review of demand for people with skills in Earth observation (Gewin, V. 2004.  Mapping opportunities.  Nature, v. 427, p. 376-377) shows that recent geopolitical and economic shifts have demonstrated their value in helping decision makers to decide.  The prospects are patchy, however.  The USA, beset by homeland security and with vast areas mapped at only a superficial level, has a thriving Earth observation jobs market, but Europe lags behind, because of better charting of its land.  To a large extent dramatic improvements in spatial and spectral resolution of remotely sensed data in the last 5 years have matched technology to a big range of applications, hence the upturn.  Many of the jobs are in governmental agencies, and are not directly related to geological skills.  That is a shame, because Earth is less well mapped than the Moon and Mars.  Yet, skills and ingenuity that you would learn in addressing purely geological challenges through remote sensing can easily be transferred to any other field.

Mantle and core do not mix

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Given the growing controversy about whether or not plumes of mantle rock can rise from the core-mantle boundary to source large igneous provinces (see Geoscience consensus challenged in EPN January 2004) the hypothesis has been tested by seeking material in hot-spot lavas that may have crossed from the outer core into the deepest mantle.  Some hot-spot lavas contain traces of Osmium-186 that may have formed by decay of an unstable platinum isotope (190Pt) that is most likely to be enriched in the core, thereby supporting the hypothesis.  Another isotopic approach is to look at tungsten (W) isotopes (Scherstén, A. et al. 2004.  Tungsten isotope evidence that mantle plumes contain no contributions from the Earth’s core.  Nature, v. 427, p. 234-237).  Tungsten, like osmium, has a strong affinity for iron, and the bulk of terrestrial W is likely to be present in the core.  One isotope 182W forms from the decay of an unstable isotope of hafnium 182Hf, whose half life is geologically short (about 9 Ma).  As a result all 182W in the Earth must have been produced in the first 60 Ma of the planet’s evolution.  Moreover, hafnium is likely to favour the mantle far more than the core, so most 182W seems likely to be present in the mantle and the core should be depleted in it.  This is borne out by comparing values in primitive meteorites with those in mantle-derived lavas; the mantle is enriched by comparison.  So, if there was significant chemical exchange between the core and mantle a lot of tungsten with very low 182W should contaminate the lower mantle.  If plumes did rise from the core-mantle boundary, then lavas derived from them ought to have anomalously low 182W contents. Scherstén and colleagues from the University of Bristol and the Australian National University show that Hawaiian lavas (the same samples used to suggest a mantle-wide plume beneath Hawaii using osmium isotopes) and South African kimberlites do not show this signature, and argue convincingly that the osmium data must represent another source of contamination, probably recycled crustal rocks.  However, that does not rule out a plume rising from the core-mantle boundary, just that the core did not play a significant geochemical role.

Collapse of the continental margin and methane release

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The vast reserves of peculiar methane-water ice deposits (gas hydrate or clathrate) in sea-floor sediments are the most likely source of methane releases that could generate sudden warming events, such as that at the end of the Palaeocene, and left traces in polar ice cores during the last few glacial-interglacial episodes.  Methane probably leaks from the sea floor all the time, but is soon oxidised to the lesser “greenhouse” gas CO2 in the atmosphere, so muting its potential effects to a low background level.  For methane to have a sizeable effect on global warming, lots of it has to blurt out suddenly.  Possibly the only mechanism that can trigger such explosive releases are failures of sea-floor sediments, either by those beneath a steep surface slope collapsing under gravity, or as a result of seismicity.  Geoscientists from University College London and the British Geological Survey have tried to correlate known peaks in atmospheric methane from the recent past (shown by ice cores) with episodes of mass flow on the seabed (Maslin, M. et al. 2004.  Linking continental-slope failures and climate change: Testing the clathrate gun hypothesis.  Geology, v. 32, p. 53-56).  They found that the periods of greatest disturbance of continental-slope sediments over the last 45 ka took place at the tail-end of the last glaciation, between 13 and 15 ka and 8 to 11 ka.  Each correlates with methane highs in the Greenlandic ice cores and with bouts of rapidly rising sea level (the Bølling-Ållerød and Preboreal warming periods).  So they conclude that there is support for a “clathrate gun” model for sudden warming associated with glacial to interglacial transitions.  However, seafloor collapses also correlate with Heinrich events (ice-sheet surges that launched iceberg “armadas” to low latitudes) that punctuated glacial times.  These marked brief periods, repeating every 1000 years or so, which mark cooling when sea-levels were low.  None are associated with upsurges in atmospheric methane., although the following interstadial warmings are.  This lack of correlation rules out a “clathrate gun” influence on millennial-scale climate fluctuations during glaciations.

Super-eruptions and climate

The biggest known, young volcanic crater is that of Toba on Sumatra, which is a caldera complex measuring 30 x 100 km.  Around 74 ka Toba emitted an eruption that dwarfed any in more recent times, and spread a dust cloud around the world – it is present in ice cores from Greenland, and has been linked with a cooling step during the onset of the last glaciation.  It happened around the time that fully modern humans had begun to spread across Asia after migrating from NE Africa – an Acheulean hand-axe has been found in the Toba Tuff – and may have deeply affected those pioneering bands.  There are older ash levels that can also be attributed to Toba eruptions, one found 2500 km away in the sediments of the South China Sea (Lee, M-Y. et al. 2004.  First Toba supereruption revival.  Geology, v. 32, p. 61-64) and at other sites up to 3000 km from Toba.  This gives an age around 800 ka.  Lee and colleagues from Academica Sinica (Taiwan), the National Taiwan University and the University of Rhode Island estimate that almost 1000 km3 of ash was expelled by the eruption.  Unlike the 74 ka ash, this layer falls in the transition from a glaciation to an interglacial period; instead of a possible cooling influence through dust blocking solar heating, there is a warming trend.  Although not quite as big as the 74 ka eruption of Toba, that of 800 ka is still vastly bigger than any other explosive volcanism during the Pleistocene.  So, it suggests that super-eruptions are not significant climate triggers after all.

Perspective on the Moon and Mars

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When an embattled US president, who as a Texan never visited the Johnson Space Flight Center in Houston, unveils plans for staffed missions to set up a lunar base and land on Mars, 10 years at the earliest after he becomes an ex-president, anyone become suspicious of an election stunt.  Former Democratic Vice-president Gore made the following observation that seems to stand above the tedium of US politics, “[It is]… an unimaginative and retread effort to make a tiny portion of the moon habitable for a handful of people”.  Much the same could be said of a Martian mission, when billions of Earthbound people find their homelands barely habitable.  The word “hubris” (insolent pride) springs to mind, for scientists who support such pies in the sky, as well as for politicians in an election year.  During the Apollo lunar missions the justification for sending people was that they could use their eyes, ingenuity and knowledge to collect samples.  The fact is that planetary scientists on terra firma specified the landing sites and told the astronauts what to collect, and of course all the sample analyses were made on Earth.  They did indeed revolutionise our understanding of how the Earth began its evolution and its record of bombardment by interplanetary debris.  Human hands were needed then, because robotics (servo-mechanisms, machine vision and remote control) were too primitive to collect material efficiently.  Within a month since Christmas Day 2003 three robotic laboratories and collecting systems have landed on the Red Planet.  One, a marvel of miniature sophistication (Beagle-2) seems to have died on touchdown.  The other two are NASA vehicles able to roam under close control and send back detailed close ups and make some analyses.  At the same time, imaging systems in orbit are providing more detail about Martian surface geology and landforms than exists for our home world, despite the efforts of geologists over the last two centuries.  Given 10 years or so of further robotic development, surface rock samples and cores of soils could be returned.  Look at it this way; a staffed mission has to send and return say 2 or 3 humans weighing upwards of 150 kg, along with all their requirements for a long mission, plus various weighty safety shields.  Given the same spacecraft without passengers, we are looking at more than half a ton of samples that could be returned for a fraction of the cost, if 2 or 3 humans forewent the massive privilege of standing on a not too welcoming planetary surface for a couple of days.

What issues remain to be addressed scientifically on the lunar and Martian surfaces?  For the Moon, the far side remains little known, but on which no human mission is likely to be landed, because it would be devoid of constant communication.  More samples of rock from the side that faces Earth would always be welcome, but robotics can grab them and bring them back.  For Mars the question is that of early life, but mainly to see if it did emerge in what increasingly seem likely to have been favourable albeit brief conditions, and if traces remain.  Geological matters are secondary to that, but nonetheless fascinating.  Yet, Mars is a far more complicated place than the Moon, and to properly grasp its evolution and composition, and whether it spawned and supported organisms, needs more than one mission to one site for a few days – all that a staffed mission could realise.  The Bush “vision” already threatens the single most important scientific instrument in orbit – the Hubble telescope.  The cost of developing human expeditions to both Moon and Mars would probably sterilise funds for more ambitious robotic exploration.  Indeed robots could invalidate their entire scientific justification long before the astronauts set off.  In order to check out the health risks of lengthy space missions, the so-far functionless International Space Station is to have life breathed into it, in the manner of a Frankensteinian white elephant.  The ageing and dangerous Shuttle fleet is to be kept alive, solely to service this legacy of Ronald Reagan’s bizarre two terms of office.  But, let’s live in the real world.  Who would stump up the funds necessary for a proper planetary exploration programme, when there will be no-one gazing steely-eyed into the camera saying how awed they are to be on Mars, Mr President?

Tectonics and climate, and the rate of mountain erosion

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It is rare for one issue of a “journal of record”, such as Nature to contain three papers on closely related topics, especially when they are geoscientific, but its 11 December issue of 2003 did.  All were about the way in which mountains erode, and attempted to measure the rates involved in three different settings.  Insofar as it is possible in Earth science, they try a reductionist approach in terms of the climatic and tectonic forces that are involved in denudation.  Getting useful timings is not as easy as it might seem with measuring fission tracks and the amount of radiogenic helium generated by decay of uranium and thorium isotopes in grains of apatite.  The principle lies in estimating when unroofed rocks rose and cooled below the temperatures at which apatite loses noble gases and the tracks in it formed by alpha particle emission heal up. In an exposed section subjected to erosion and isostatic uplift the higher rocks should record older ages than those lower down, the difference representing the pace of erosion and uplift.  There is, as yet, no way that periods less that 500 thousand years can be resolved by either method, and in terms of recent climate that can cover several glacial-interglacial cycles.

The simplest of the case studies was in the Cascade mountains of the NW USA, where there has been minimal tectonic activity, but a great deal of rain over the last few million years.  The crust has risen as material was stripped off the mountains. The average rates of erosion on time scales of millions to tens of million years closely follow the modern variation in precipitation over the area (Reiners, P.W. 2003.  Coupled spatial variations in precipitation and long-term erosion rates across the Washington Cascades.  Nature, v. 426, p. 645-647).  As a result, western parts of the range where rainfall is far higher than in the eastern rain shadow could be expected to be rising as much as three times faster, if a balance between erosion and isostatic uplift has been achieved. Since erosional power is expressed by rainfall and surface gradient, the fact that average erosion rates do not correlate well with topographic relief suggests that precipitation has outweighed the effects of slope steepness.  The opposite seems to hold in the Himalaya of central Nepal, which show the most gross variations in precipitation, due to monsoonal conditions (Burbank, D.W. and 7 others 2003.  Decoupling of erosion and precipitation in the Himalayas.  Nature, v. 426, p. 652-655), yet long-term erosion rates do not vary very much, except between the topographically distinct Lesser and Greater Himalaya ranges.  The Himalaya are altogether more geologically and tectonically complex than the NW USA, so finding such little variation is as interesting as it seems currently inexplicable.  The lack of correlation in the Greater Himalaya between precipitation (a five-fold decrease from south to north across the range) and erosion rates (more or less constant and high) suggests that tectonic uplift is the main driving force.  Much the same findings from the area immediately to the east in the Nepalese Himalaya, though using a mica Ar-Ar thermochronology method that spans a longer period, have been interpreted very differently (Wobus, C.W. et al. 2003.  Has focused denudation sustained active thrusting at the Himalayan topographic front?  Geology, v. 31, p. 861-864).  Wobus and his colleagues from MIT suggest that rapid rise of the Greater Himalaya (~10 km in the last 10 Ma) was induced by isostatic uplift driven by erosion, even maintaining movement on the huge bounding thrusts to the orogenic belt.  Altogether more complicated is the erosion of Taiwan, which is seismically active, has a complex tectonic history that affected rocks of very different strengths in different areas and is subject to a highly variable maritime climate (Dadson, S.J. and 11 others 2003.  Links between erosion, runoff variability and seismicity in the Taiwan orogen.  Nature, v. 426, p. 648-651).  They detect changing patterns of erosion as deformation has migrated.  Attempts at correlation between modern erosion rates and various factors came up with only two of significance, with recent seismicity and typhoons.  Each triggers landslips that instantaneously add debris to flowing rivers.  Precipitation rates, river discharge, slopes and stream power showed little link with erosion rates.  Of the four papers, only one (Wobus et al.) is able to relate differences in the erosive power of streams to the contrasting erosion rates of the Greater and Lesser Himalaya.

Such a hodge-podge of seemingly conflicting findings, based on studies that use supposedly revolutionising techniques, must worry agencies who have been induced to part with large funds to support fission-track and (U-Th/He) dating facilities supposedly to advance geomorphological studies.  Peter Molnar, who with Phillip England first reviewed the complex interplay between erosion, tectonics and uplift, and their counter-intuitive outcomes, made the following pithy comment, “The differences among these papers call attention to the inadequacy of current theory, without which one gropes for a way to plot data”.  Plainly, there has been over-excitement about techniques in the hope of empirically deriving theories, which has resulted in half-cocked research, and some gullibility among funding bodies.

See also:  Molnar, P. 2003.  Nature, nurture and landscape.  Nature, v. 426, p. 612-614.  New Scientist (31 January 2004) includes a 12 page special report on the technological issues involved in the Bush vision.

Rationalising radiocarbon dating

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The use of radiometric dating based on the decaying away of radioactive 14C is the most useful technique for building sensible archaeological and climatic records over the last 50 thousand years.  However, this radiocarbon is produced from 14N by cosmic rays in the upper atmosphere, and their flux varies with time.  Consequently, the proportion of 14C in the environment varied in the past, and a radiocarbon age is not necessarily an age in calendar years “before present” (BP).  Even BP is confusing, because it isn’t “before now” but before 1950 when the first hydrogen bombs produced 14C.  The outcome is one of some confusion.  If dates were recorded in calendar years, whether BP or AD/BC everything would be clear.  But they aren’t.  Many authors give their dating as either 14C ages (BP) or calendar years (BP), and the two can be very different.  For instance, the date when the Younger Dryas glacial pulse began is 1000 calendar years older than its 14C age.    One reason for the dichotomy is that no agreed conversion existed until about 1998, particularly for the time before which annual growth rings in trees can be built into an unambiguous record, using modern trees and those preserved in ancient timber.  Bristlecone pines and other long-lived trees first gave an accepted conversion factor that went back around 6000 years.  That has been extended to about 26 ka by dating annually layered corals, stalagmites (speleothem) and sediments.  A way of going even further back is correlating large, world-wide events between their appearance in a record such as a marine sediment core, dated using 14C, and their appearance in a Greenland ice core, whose annual layering gives a calendar age.  However, further back in time less radioactive 14C remains to be measured and contamination by later carbon introduced by percolating water blurs the dating.  In September 2003 the 18th International Radiocarbon Conference tried to clear the air (Bard E. et al. 2004.  A better radiocarbon clock.  Science, v. 303, p. 178-179).  The latest “official” calibration curve, (INTCAL04) goes back to 26 ka.  But beyond that there are 3 quite different candidates for calibration, the sea-floor sediment-ice core curve, one based on annually layered lake sediments in Japan, and one from speleothem in a submerged cave in the Bahamas.  For a vitally important archaeological find, such as the paintings in the Chauvet cave in France, the 14C date of 31ka could range from 33 to 38 ka in calendar years.  Dates for fossil occurrences of Neanderthal and the first fully human Europeans could overlap or be so different that neither had an influence on the other.  Everyone hopes that the sea-floor sediment-ice core curve can be validated by new results, thereby giving a common age framework to all dateable materials.

Ancient baby penis worm hits the news

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China is proving to be the repository of a vast wealth of well-preserved ancient faunas, thanks to several lagerstãtten, the most famous being that which hosts early ancestral birds that show links with dinosaurs.  But Chinese strata with exceptional preservation also occur in Cambrian sediments, close enough to the first appearance of preservable life forms to make any out-of-the-ordinary finds especially revealing.  Ten years ago many palaeontologists scoffed at reports of trilobite embryos being unearthed in southern China, yet there has been a steady flow of material that opens up what might be called “palaeoembryology”.  Being able to describe and analyse an entire life cycle of an organism is vital in studies of the inter-relatedness of living metazoans.  The lack of data on fossil life histories to some extent thwarts attempts to place extinct animals accurately within an evolutionary scheme.  Palaeontologists from the University of Bristol and Peking University have therefore put such studies on the map through finding exquisitely preserved Cambrian embryos of what is now a rare and bizarre animal group, but one thought to lie at the root of the explosive radiation of the arthropods, which includes insects (Dong, X. et al.  2004.  Fossil embryos from the Middle and Late Cambrian period of Hunan, south China.  Nature, v. 427, p. 237-240).  They are in eggs, and therefore had yet to hatch and develop further; true embryos, from their initial development to the last stage before emerging.  They are Scalidophores, which include today the individual phylla of Priapulida, Kynorhyncha and Loricefera, all marine worm-like animals (the priapulids are the notorious, and fortunately rare, penis worms from their evocative contours).  Interestingly. the embryonic stages clearly indicate direct development from egg to adult, rather than going through the intermediary larval stage that characterises most insects and other invertebrates.  Such direct development seems to be a primitive evolutionary stage from which more complex life-histories developed later.  Penis worms are well known to grow hugely once hatched, so the search is on for a fully grown adult from the Cambrian of southern China, as well as early developmental stages of other animal groups..

See also: Budd, G.E. 2004.  Lost children of the Cambrian.  Nature, v. 427, p. 205-206.

National Geochemical Survey of the USA

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The US Geological Survey has made publicly available a large repository of geochemical data (63 of the 91 naturally occurring elements) that it has acquired through a continuing nation-wide survey of stream sediments (available at http://tin.er.usgs.gov/geochem/doc/home.htm).  The data coverage is incomplete and involves several generations of previous surveys.  The most revealing stream sediment surveys involve collection of panned sediment samples in every small stream that has no upstream tributary, but that is a daunting task for such a vast area as the USA.  That method allows the analyses to be treated as accurate representations of stream sediment composition in upstream catchments around 1 x 1 km in size.  The USGS data are a mixed bunch, some dating from the National Uranium Resource Evaluation (NURE) of the 1970s when there was a scramble to find new uranium ore bodies.  The NURE survey involved a sample density based on a 17 x 17 km grid, and made no distinction between stream order.  The latest USGS survey is based on sample collection that uses 10 x 10 km grids drawn in the UTM co-ordinate system. Each 10 x 10 km cell is divided into four quadrants, and one is selected at random for sampling.  In that one small stream selected at random is chosen for analysis.  The data set is too coarse and too varied to create meaningful gridded interpolations that can be displayed as continuous tone images, unlike comparable geochemical atlases based on systematic, small-stream sampling, such as that developed for commercial leasing by the British Geological Survey. The NGS data will be a useful resource for scanning broad geochemical features of the country, such as for high levels of potentially toxic elements in water, bearing in mind that the analyses are of solid minerals not the water itself.

“Plumeology” site

The last issue of EPN showed that the debate over mantle  plumes, their sources, and even their existence is hotting up (see Geoscience consensus challenged in EPN January 2004).  However that pans out, vast areas of continental and submarine flood basalts compel geoscientists to ponder over them, the more so because they represent events never witnessed by humans and are therefore unimaginable.  Now they have their own website (http://www.mantleplumes.org/) that has been compiled by Gillian Foulger of Durham University.  It is an impressive and highly useful resource, the outstanding feature being pages on most aspects of large igneous provinces written by experts who are also excellent communicators.  There is even a linked site at the Geological Society that hosts discussion on the Great Plume Debate, as well as a letters page, links and up to date news.  For information, without unnecessary frills, this is the place to go, especially if you have to write an essay!

Influence of continental weathering on climate boosted

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Since the resurrection of Chamberlin’s idea that the rate of chemical weathering of continental crust helps regulate atmospheric CO2 by Maureen Raymo, the hypothesis has not yet been supported by convincing geochemical evidence.  There is such a lag between changes in ocean chemistry and evidence for global climate change, that correlations are flimsy.  The need is for a proxy for weathering of the land surface that resides in seawater for a geologically very short period.  Such an element is osmium (Os), which passes from river water through the oceans to sea-floor sediments in about 25 thousand years, so changes in its abundance in sediments ought to match the pace of any climatic shifts.  In principle, there are two main sources for elements in seawater, from sea-floor hydrothermal alteration of oceanic crust, and from continental weathering.  The first can be considered to be more or less constant, except on time scales of tens of million years.  Continental weathering is a response to climate change, and keeps pace with it.  Researchers at the UK Open University and the University of Köln in Germany analysed samples for osmium and carbon isotopes through a sequence of Jurassic mudstones on the NE coast of England (Cohen, A.S. et al. 2004.  Osmium isotope evidence for the regulation of atmospheric CO2 by continental weathering.  Geology, v. 32, p. 157-160).  The carbon isotopes show a sudden drop in d13C within a very hydrocarbon-rich unit famous for it contribution of jet (oil-rich lignite) to Victorian funereal jewellery.  This negative excursion is recognisable world-wide at around 180 Ma.  The most likely explanation is a monstrous blurt of methane from destabilised gas hydrate on the Jurassic sea floor (see Methane hydrate – more evidence for the ‘greenhouse’ time bomb, August 2000 issue of EPN).  The Jet Rock of the Whitby coast therefore preserves a nice example of sudden climatic change, and by the end of its deposition carbon isotopes returned to Jurassic background values.  Methane, a powerful “greenhouse” gas, is rapidly oxidised to CO2 in the atmosphere, so reducing its initial warming effect, but climate would have been hotter for some time afterwards until the excess CO2 was drawn down somehow.  Interestingly, the Jet Rock also shows a sudden leap in the abundance of 187Os, reflected in the 187Os/186Os ratio of the samples, and an upward step in the value of the 87Sr/86Sr ratio – one of the fastest rises known.  The latter is generally assigned to an increase in continental weathering, since continental crust contains more radiogenic 87Sr than does oceanic crust.  The implication of the osmium-isotopic shift is odd; it requires an increase in the rate of continental weathering by 4 to 8 times that in the preceding period.  That is a vast change, even if it only lasted for a short period, but it tallies with what is known about the temperature dependence of the dissolved loads of rivers in more recent times.  If the osmium isotope excursion truly reflects massive continental weathering, then it is possible to calculate the drawdown of the excess CO2 in the atmosphere from a commensurate flux of calcium and magnesium ions from the continents, that would eventually form marine carbonates.  The authors estimate a mere 37-123 ka to get rid of it.  Yet continent-derived radiogenic 87Sr remained high for much longer, and the authors’ arguments become tricky.  One interesting aside is that, unlike today, more groundwater found its way to the oceans than surface run-off during the Jurassic, perhaps 6 times more.  It is easy to look on weathering as what happens at the interface between rocks and the weather; the land surface.  Not so.  A great deal of chemistry that releases soluble ions goes on in the subsurface, above and below the water table.  It is by no means as simple as reactions between carbonic acid in rainwater and silicate minerals.  Weathering is the product of hydrogen ions’ (whatever their source) effects on silicates.  Bacteria are extremely important actors in modifying pH below the surface, for example the sulphate-sulphide reducers, and the oxidative dissolution of sulphides produces sulphuric acid.  Even more interesting for the chemistry of groundwater is the curious role of iron hydroxide.  Under oxidising conditions it adsorbs many elements from solution, including platinum-group elements, such as osmium.  Should conditions become reducing, dissolution of goethite skins on sedimentary grains releases the accumulated elements.  A warming trend almost inevitably results in increased precipitation, and rising water tables.  It also should boost biological productivity on land and an increase in the amount of buried organic matter, which create reducing conditions in groundwater.

Protecting your intellectual property

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Long ago, most students entered research by thinking up their own project, albeit with advice from potential supervisors.  That is rarely possible today, for many reasons.  Instead, gifted students are recruited to research topics proposed to funding agencies by established scientists.  More often than not, such projects slot into an overall strategy centred on an academic’s career or the ambitions of a research group.  There are advantages in having the sometimes undivided attention of a “boss”, a structured approach to work within a broader framework, access to a group’s equipment and funding, and support from several co-thinkers.  With the old style, there were risks in “ploughing a lone furrow”, such as abandonment by a disenchanted supervisor (the enchanted ones could be even more worrying).  The single most important advantage of designing your own project, hard and risky as that might be, was one of possession from the outset.  Such responsibility develops qualities that are otherwise not easy to get: independence of thought and action, time-management,  resourcefulness, an ability to argue your case, and self-discipline – if you can really “hack” it.  Except for the indolent and irrecoverably stupid, most people can, given some knowledge of where their subject is going and thesine qua non of curiosity.  In those “old days”, the risks were more than offset by the advantage of ownership, and it was rare for postgraduates not to be successful, and the majority gained their doctorates within three years.  Today, up to a third of enrolled graduate students withdraw or fail their degrees, and hardly any complete inside this reasonable period.

Funding agencies now demand guarantees that their outlay bears fruit.  They increasingly direct lines of research, so that studentships follow previous funding.  The funders are more accountable, and by the iron logic of the marketplace so too must be the recipients.  The upshot is continual assessment of research performance by departments, the creation of “centres of excellence”, and the crushing of departments that do not measure up to an amoebic growth of criteria and guidelines.  So, for anyone keen on testing their abilities to the limit and following their curiosity, the options are increasingly limited.  Even if you have independent means, it is now a very rare department that encourages self-motivated research by students, or even by its established staff.  In truth, most academics find it hard to be independent, because they no longer have the security that once guaranteed freedom of thought, action and expression.  In Britain, if an academic began their career or earned promotion after 20 November 1987, they can be dismissed solely on grounds of redundancy, rather than “with good cause”, which was the rock on which tenure used to be based.  “Gross moral turpitude” was, I believe, the operative and infinitely more expressive phrase in US institutions.  So for your average supervisor the world has turned upside down.  Now it’s a case of “publish or perish”, larded with citation and impact records, and bringing cash into your institution to boost its research assessment.  There are very few academics with the energy, imagination, brass neck and wit to jump through all these hoops and remain sanely independent.  So we see a growth of hidden but nonetheless unwholesome vices adopted by some to survive and prosper in this deranged environment.  There are many victims, but the new researcher is most at risk.  During the festive season it is customary to give and receive advice, as well as greetings.  Here is some that concerns the vice that dare not speak its name –plagiarism – in the form of a bestiary to help you memorise potentially risky people.

  1. Chameleons Check out potential supervisors.  The Science Citation Index will reveal their record of sole or senior authorship of papers (notreviews).  If they are what they claim to be, that will dominate.  Relative to that, how many times does their name appear within multi-author papers, of which they are not senior author?  If the latter dominates, their reputation probably rests on offering technical facilities that they control, or the research talents of other people.  You may find individuals who have a short publication list of either kind.  They are either at the start of their career, or beyond all human help (except perhaps your own).
  2. Beavers Never let anyone else do any work for you, unless they are a kindly technician (who then deserves at least an acknowledgement).  Where possible, keep your research materials under your personal control – in some institutions burial is a useful tactic.
  3. Curlews Be suspicious of a supervisor who shares your findings with the rest of a team; either you do that yourself or not at all.
  4. Moles Although communication with others is an essential aspect of research, until you are ready to submit a paper for peer review, do not reveal all in seminars and conferences.  Pay particular attention to your posters.  At every conference you will see people photographing them, whom you can safely assume are after your ideas.
  5. Hamsters Beware the friendly soul offering, without being asked, to read your first draft of a paper.  Instead, plead with the most curmudgeonly academic around, the one who hammers your every utterance, for he or she will probably be honest.
  6. Tapeworms Do not allow your supervisor to routinely add their name or others in a research team to your papers.  Authorship is not based on advice, basic training in research techniques or discussion of your work.  That is your supervisor’s duty of care, and a good one should give far more than they take. Acknowledgements are the place to express gratitude for such assistance.  Authors have to do real work, both analytical and intellectual, to deserve a place in the list.
  7. Squirrels Insist that your supervisor lets you read all drafts of their papers that bear on your own field, to check that your findings are not included, as well as to learn.  If your work appears, you have a right to authorship.
  8. Weasels Be aware of the relationships among academics and post-docs in your department, and theirs with others in outside institutions.  Keep an eye on “networking”, which often involves mutual sharing of information as well as gossip, particularly if joint bids for funding are in the offing.
  9. Ravens It is easy to be pressured overtly and subtly, particularly in a large research group.  That may be beneficial, but can be to get you to toe the “party line”.

10.  Wolverines Never tolerate anything that seems like plagiarism, manipulation, obstruction, exploitation, bullying or harassment.   Best to confront politely yet firmly the person responsible, but that is not easy.  Finding someone who can help is not easy either.  Your institution may well have a policy of pastoral care based on designated individuals, who are deemed to be disinterested and trustworthy.  In the real world there is a culture of protecting long-term colleagues, which extends throughout a university; you are transitory…  In case of difficulty, ask to change your pastoral advisor.  Other students of longer standing may know who is straight, or have similar experiences.  Whatever, it is essential that you get honest support to resolve such problems.  One useful tactic is to air your grievances as accurately as possible in writing, with a copy to someone that you can trust.

11.  Diverse enchanted beasts The most difficult obstacle to ownership can be, oddly, the genuinely honest, kindly and enthusiastic supervisor.  Because of their greater experience and breadth of knowledge, your work can easily become their obsession, usually because of their frustration with your progress.  They will not steal your thunder consciously, but can easily end up driving you rather than the other way round.  If you want to become their creature, fine.  If not, then you have battles ahead, but they will serve both of you well!