Homing in on the great end-Permian extinction

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Discussing what actually killed off around 95% of all species 251 Ma ago has become the perennial mass-extinction topic, now that the K-T boundary event is more or less done and dusted, bar a little murmuring over the Deccan Trap.  Michael Benton of the University of Bristol has summarised the current state of play for the Permian-Triassic (P-Tr) event (Benton, M. 2003.  Wipeout.  New Scientist, 26 April 2003, p. 38-41).  Despite many attempts to link an impact to the annihilation – such evidence as there is (see Buckyballs and the end-Palaeozoic extinction, EPN March 2001) has not been reproduced by independent analysis of the material.  Weighty evidence comes instead for an Earth-induced event, from the coincidence of the monstrous Siberian Traps with the 100 thousand years or less that the extinction occupied, and from complete sequences across the P-Tr boundary in a Japanese ophiolite and a shallow marine section at  Meishan in South China.  As well as an intricate series of faunal changes, the Meishan sequence has now provided a complete record of oxygen and carbon isotopes that span the boundary event.  The oxygen data suggest a 6ºC rise in global temperature at exactly the stratigraphic level of the extinction and of a massive lurch towards light carbon.  Such a high proportion of 12C occurs at the boundary that it cannot have been induced by sterilisation of the oceans, which may well have happened as a result of the extinctions.  Nor can even the huge belch of mantle CO2 emitted by Siberian continental flood basalts.  The two combined only account for 40% of the carbon-isotope excursion.  Release of methane from long-term storage as gas hydrate on the Permian sea floor is the only conceivable candidate.  So it looks as if a runaway “greenhouse”, plus toxic gas and maybe acid rain put paid to most living things.  Such a wiping out left lifeless oxygen-poor oceans – originally dubbed “Strangelove oceans” by Ken Hsu after the eponymous insane doctor.  Triassic times did not see explosive reoccupation of abandoned niches, recovery taking up to 50 Ma from a tiny population of not very diverse organism.  Benton has written a book on the P-Tr event (When Life Nearly Died.  Thames & Hudson), and that is likely to be a rattling read. New Scientist maintains it’s irritating habit of never referring to sources in its articles, so to go further, you will have to buy the book.

Microbes showed no sign of change following a “Snowball Earth”

The “Snowball Earth” hypothesis has suffered quite a lot since its original promotion (see: Meltdown for Snowball Earth?, February 2002 EPN; Snowball Earth hypothesis challenged, again, December 2002 EPN).  Whatever the eventual fate of the notion that the entire Earth was iced over from pole to pole, the fact that glaciers reached sea level at low latitudes at least twice in the Neoproterozoic seems to be an established fact.  Such climate swings must surely have had an effect on life, either by driving up the rates of extinction and adaptive radiation because of stress, or perhaps providing nutrients to the oceans in vast amounts that allowed the phytoplankton base of the food chain to explode (see: The Malnourished Earth hypothesis – evolutionary stasis in the mid-Proterozoic, September 2002).  One of the first discoveries of low-latitude glaciogenic deposits was around Death Valley, California by the late Preston Cloud, who worked there during the 1960s.  So it is fitting that palaeobiologists associated with the Preston Cloud Research Laboratory at the University of California, Santa Barbara have dissected sediments within and immediately beneath the 750 Ma diamictites that Cloud interpreted as glacial in origin, to test for signs of evolutionary change (Corsetti, F.A., Awramik, S.M. & Pierce, D. 2003. A complex microbiota from snowball Earth times: Microfossils from the Neoproterozoic Kingston Peak Formation, Death Valley, USA.  Proceedings of the National Academy of Science, v. 100, p. 4399-4404).  In cherts within carbonate units they found a surprisingly diverse range of undoubted microfossils, that are probably auto- and heterotrophic Eucarya, but no difference between pre-glacial and glacial levels, in terms of their biota.  Although this single piece of work does not prove that there was no biological change associated with a major cooling during the Neoproterozoic, it does cast doubt on the severity of its effects on life.  Most important, the study shows that well-preserved cellular material is available for study in sediments that occur with glaciogenic diamictites, and should open up a new line of research bearing on the rise of the metazoan (multi-celled) Eucarya, which appeared in large numbers shortly after the last (~600 Ma) glacial epoch.  Most if not all Neoproterozoic carbonates, whose universal presence in close stratigraphic proximity to glaciogenic strata first hinted at low-latitude frigidity, contain abundant chert nodules that are the best preserving medium for delicate and tiny cell structures.

No glacial refugia in the Amazon Basin?

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Tropical rainforest in Africa and South America is the most diverse biome on the planet, both as regards plants and animals.  One view of how such luxuriance arose is that the forests have blanketed the humid tropics for as long as 50 or 60 million years, and the fact that they encompass a huge variety of environments created by different levels in the dominant and diverse vegetation.  Thousands of niches and the interactions between organisms that exploit them during lengthy stasis inevitably drives rapid evolution towards all kinds of specialisation.  The other view is that rainforests are by no means static over millions of years, but climate shifts have caused them to retreat and advance, perhaps hundreds of times during the Cenozoic.  Amazonia in particular shows surprising variation in diversity, some patches being far more biologically rich than others, and having regionally distinct assemblages of plants and animals.  This theory suggests that climatic stress, probably drying associated with globally cool episodes, resulted in rainforest shrinking to “refugia”.  In them, populations of plants and animals shrank, thereby reducing the gene pool and giving greater chance for evolution by natural selection; different in different refuge areas.

Tropical soils are continually reworked and their highly oxidising nature destroys organic remains.  So no record of its development exists in rainforest.  However, wind and rivers transport spores, pollen and other biomarkers to seafloor sediments, where a complete record of fluctuations in biomass and diversity becomes preserved.  A test of the popular refugia hypothesis is therefore to analyse organic matter in continuous cores taken from offshore sediment.  Known fluctuations in global climate, from the oxygen isotope record should be matched by changes in the record of terrestrial biomarkers carried to the sea.  Cores from the deep-sea sediment fan off the mouth of the Amazon potentially provide such a test (Kastner, T.P. & Goñi, M.A. 2003.  Constancy in the vegetation of the Amazon Basin during the late Pleistocene: Evidence from the organic matter composition of Amazon deep sea fan sediments.  Geology, v. 31, p. 291-294). Kastner and Goñi, from the University of South Carolina, examined phenols and organic acids in the cores, which can discriminate between grassy plants and trees that would have dominated savannah and rainforest, whose relative cover of the Amazon basin should have changed, according to the refugia hypothesis, as climate shifted from globally cool-dry to warm-humid..  Although their record only spans the last glacial cycle since 70 ka, they detected no significant change in the proportion of grasses and trees in the Amazon catchment.  Moreover, the biomarkers remained similar to those carried by the Amazon today, right through the last glacial maximum, when drying of the tropics would have been most likely to have driven a shrinkage of rainforest area.  It seems unlikely that forest refugia developed during one of the most extreme climate shifts in the last 55 Ma.  Global climate fluctuations were considerably less before 1 million years ago, when the current round of 100 ka cycles began.  So there is little reason to doubt that the Amazon rainforest has had a more or less constant area for much of the Cenozoic.  The same cannot be said for those in Africa and SE Asia, partly because there are no useful data from offshore sediments, but also because those regions have experienced changing topography due to major tectonic activity, whereas eastern South America has remained stable.  To conclude, as the authors do, that the data signify no great fluctuation in rainfall is not so certain.

Catastrophic floods and denudation

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Working out the rate at which landscapes evolve depends on some means of dating surfaces formed at different stages in the cutting down of topography.   Modern studies rely to a large extent on the build up of isotopes, such as 10Be, that form in minerals no more than a metre or so beneath the Earth’s surface when they are exposed to cosmic ray bombardment.  If such transmuted nuclides stay in place, for instance on a relic surface or a series of alluvial terraces, cosmogenic isotope analysis dates the formation of that surface.  No matter how precise such surface dating can be, and currently there is a slop of around 20% either side of an age, there is a limit to the number of suitable surfaces.  So, the continual degradation of landscape can only be sampled at a few isolated times.  At best, an average denudation rate over long periods is all that geomorphologists can hope for.  The same goes for analysis of the range of times during which grains in a sediment were exposed to cosmic rays, before they were eroded, transported and finally protected from bombardment when they were buried in alluvium, that is another approach to timing erosion.  Average rates of erosion are useful in assessing some aspects of landscape development, but they are not much good for judging how it took place.  Standing in some awesome scenery easily gives the impression that it must have evolved by some continuous, steady process, and there is a long tradition dating back to James Hutton that views surface processes in that way.  Changes in rates have been seen as responses to “rejuvenation”, either by falls in the base-level of erosion or tectonic uplift to add gravitational potential to a region that makes flowing water more energetic.

Another approach is to look at the actual transfer of mass, either carried by rivers during different seasons or in the volumes of sediments that were deposited by recognisable individual events, such as a flood.  In large river basins that have a low average gradient it is well-accepted that occasional floods don’t have much effect on sediment movement in the long term, but most of the sediment moved in such basins is alluvium already supplied by earlier processes.  In mountainous areas rivers carry material directly from bedrock and the regolith that lies on it.  Anyone who has witnessed flash floods in a normally crystal clear mountain river knows their awesome power.  They become mud torrents studded with boulders that even fly through the air; they are debris flows rather than streams in the normally accepted sense.  Such flows are episodic, but frequently annual, and exert a major influence over denuding the landscape.  Yet over millennia, they too should maintain a consistent down wearing.  In the Appalachian mountains of the eastern USA denudation rates seem to average out between 2.5 to 5 centimetres per thousand years.  However, four catastrophic Appalachian storms in the late 20th century, related to hurricanes, had an astonishing effect on erosion there (Eaton, L.S. et al. 2003.  Role of debris flows in long-term landscape denudation in the central Appalachians of Virginia.  Geology, v. 31, p. 339-342).  Carbon-14 dating of ancient mass-flow deposits formed in Virginia by comparable storms indicates recurrences in particular drainage basins around every 2500 to 3500 years.  During that time the average rate of erosion would have denuded the surface by a measurable amount (5 to 10 cm), yet the recent storms removed between 47 to 63% of that expected during periods measured in millennia.  The Appalachians are well vegetated, and therefore well protected from the effects of extreme floods compared with the surfaces of really big mountains such as the Himalaya and rugged areas in arid regions.  The obvious question is, “Are average denudation rates, no matter how precise, very relevant to the way landscapes actually develop?”  It is an important one, because weathering of debris from mountains is regarded by many geochemists as a means of taking carbon dioxide from the atmosphere – silicate weathering that involves CO2 dissolved in rainwater locks atmospheric carbon in bicarbonate ions that carbonate-secreting creatures in the sea can sequester to deep storage when they die.  If about half the erosion of mountains is in widely separated catastrophes, which shift and then dump debris in a matter of days, then it is possible that the sums based on equating rates of weathering with those of erosion are not entirely valid.  Weathering of continental silicates is one means of forcing global cooling by reducing the greenhouse effect, and understandably mountain rivers teem with researchers sampling the water and sediment load, especially in the Himalaya.  If the bulk of debris shed to plains, such as those of the Indus, Ganges and Brahmaputra, never had time to be weathered at high altitude because it moved in catastrophic pulses, then maybe the sampling should be done somewhere else.  Processes in the vast alluvial tracts far below high mountains are slower and more constant wit time, so maybe looking at groundwater that moves through them might add to the current research..

When the Mediterranean dried up

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At the end of the Miocene (from 6 to 5.3 Ma) the connection between the Atlantic Ocean and the Mediterranean Sea was blocked somehow.  Over 700 thousand years evaporation deposited a thick layer of salt that now lies beneath much of the Mediterranean basin.  This is known as the Messinian salt crisis.  Equally dramatic, the straits reopened suddenly to allow seawater to flood back in the early Pliocene, in a hydrological catastrophe.  How the Mediterranean basin became cut off has been ascribed to a 60 m sea-level fall, crustal shortening associated with nappe formation in the Betic Cordillera of Spain and the Atlas mountains, or by some kind of tectonic uplift.  Timing of the Messinian crisis rules out the first two options, but sedimentation in the former “gateway”, a shallow seaway through what is now southern Spain, shows evidence of rapid shallowing that would have resulted from regional uplift.  The question is, what drove this regional upwarping?  A team from the GEOMAR Research Centre for Marine Geosciences in Kiel, Germany has discovered evidence from the changing geochemistry of Miocene to Pliocene volcanic rocks in the western part of the Mediterranean (Duggen, S. et al, 2003.  Deep roots of the Messinian salinity crisis.  Nature, v. 422, p. 602-606).  Send Duggan and his co-workers found that the lavas underwent a geochemical shift  from affinities with subduction-zone processes to those typical of intra-plate magmatism around 6.3 Ma ago, volcanism largely ending about 4.8 Ma.  The ending in the late Miocene of eastward subduction of Tethyan sea floor beneath the Mediterranean, which had initiated volcanism around 12 Ma, led to foundering of part of the lithosphere and uprise of asthenosphere.  This is marked by a change from high-silica, early magmas to alkaline, more basaltic varieties during the period of the Messinian salinity crisis.  Uplift resulting from this delamination would have pushed the formed connections between the Atlantic and the Mediterranean as much as 800 m above sea level.  Duggan et al. Suggest that the axis of uplift gradually migrated westwards, so that by the end of the Messinian crisis the area now centred on the Straits of Gibraltar would have been bulged up.  Massive gravitational sliding from this edge of the continental lithosphere into the Atlantic may then have opened the narrow passage through which Atlantic water once again flooded.

Flying feathers

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Steadily, the remarkable fossil record in Cretaceous terrestrial sediments in China is revolutionising ideas about vertebrate evolution, particularly among small dinosaurs and early birds (see The Early Cretaceous lagerstätten of NE China in EPN March 2003).  The long-held view that birds simply emerged fully fledged and flying from the dinosaurs has had to be thoroughly amplified.  The sheer diversity, combined with intricate preservation in the Chinese sediments reveals feathering on a host of animals that are not birds, but earlier, bipedal dinosaurs.  Some may have flown, but others had feathers for some other reason.  Feathers are not a prerequisite for flying, and are so odd and complex in morphology and growth, that it has always been probable that they emerged and evolved over a long period preceding the appearance of true birds.  Now it is possible to begin dissecting that strange evolutionary divergence, and Richard Prum and Alan Brush of the Universities of Kansas and Connecticut combine information about feathers and discussion of new fossils in a superbly illustrated review in the March issue of Scientific American (Prum, R.O. & Brush, A.H. 2003.  Which came first, the feather or the bird.  Scientific American, March 2003, p. 60-69).

Squirrels and tectonics

The squirrel family (Sciuridae) is one of the most widespread groups of mammals, only Australia, the Pacific islands and Antarctica being squirrel-free.  The main reason is that squirrels are basically a primitive group among the rodents, themselves accounting for almost 50% of all living mammals species.  The earliest fossil squirrel (Douglassciurus jeffersoni) was found in Late Eocene sediments in western North America, and the family seems to have originated there.  The present wide distribution of squirrels bears witness to the many opportunities for migration in the Palaeogene, when continental masses were much less dispersed than they are today, together with changing environmental conditions that would have acted to drive migration.  In the same way as human migrations have been charted and timed using genetic sequencing and molecular clock hypotheses, this unique group has been studied in detail (Mercer, J.M. & Roth, L. 2003.  The effects of Cenozoic global change on squirrel phylogeny.  Science, v. 299, p. 1568-1572).  The general picture outlined by Mercer and Roth is that the Sciuridae migrated first across Beringea to reach Asia, then Europe and eventually Africa.  In terms of migration rates, this was fast, the earliest European squirrel (Palaeosciurus) occurring in Early Oligocene sediments – this is also the earliest representative of squirrels that bear signs of the distinctive chewing muscles whose use today delights us all.  Near identical musculature is found in the Red Squirrel and many other tree squirrels (Sciurus sp.), and their “living fossil” anatomy is borne out genetically.

As well as giving a fascinating insight into how modern genetic techniques help organise the cladistics of animals, the paper is full of information about the sheer diversity that this lowly group has achieved in about 50 Ma.  Ground squirrels, rock squirrels, marmots, and tree squirrels abound, but none are so fascinating as the flying squirrels.  Their teeth are similar to those in early Oligocene fossils, and genetic analysis suggests a common ancestry relatively early in squirrel evolution and migration.  However, fossils of flying squirrels, in the areas where they are found today (North America and Asia) appear quite late in the stratigraphic column.  The authors suggest that perhaps flying ability arose several times independently, based on a labile trait in the genes of their clade.  There is also evidence for population “bottlenecks” that preceded adaptive radiation in several area.  For instance, the entire radiation of South American squirrels seems to have stemmed from a single lineage that crossed the Isthmus of Panama shortly after it formed in Pliocene times.  African squirrels can be accounted for by just two colonisations in the Miocene, and those of Indonesian archipelago east of the Wallace Line by migration during the Late Miocene, when sea-level was at its lowest before the Pleistocene lowstands.  Most astonishing of all, is the Giant Squirrel of Borneo (Rheithosciurus), which is genetically closest to the squirrels of North America rather than its more diminutive cousins in the Sunda Shelf islands – did its ancestors move with astonishing speed, or did all related squirrels along its migration route become extinct quite rapidly?

A possible answer to the origin of the Giant Squirrel of Borneo lies in a collection made recently from a unique lagerstätten in a clay-filled pocket within laterites of northern Karnataka in India.  The discoverer, Dr P.U. Siffli of Sringeri Institute of Palaeontology, has posted provisional results on his web site (http://geocities.yahoo.com/pusiffli/squirrels.html).  The range of fossil rodents from near Sringeri is astonishing.  Among them are bones of an undoubtedly primitive squirrel of enormous dimensions – approximately the size of a large child.  Its masticatory musculature is similar to that of the North American Douglassciurus jeffersoni of Eocene age, i.e. unlike that of modern tree-squirrels.  The biggest surprise lies in the dentition of the Sringeri giant squirrel.  The typical rodent second incisors are serrated and arranged in a similar way to the shearing canines of mammalian carnivores.  Its back teeth bear close resemblance to carnivore carnassials.  As if this was not sufficient, the body cavity of the best preserved fossil contains pellets made up exclusively of bones from primitive hamsters, which abound in the lagerstätten.  In a personal communication, Pandit Unmer makes a convincing case that he has discovered the only known predatory squirrel (provisionally named Titanosciurus sringeriensis), and will soon submit his finding for peer review.  His only regret is that establishing a stratigraphic age for the laterite-bound pocket is proving to be very difficult.  Sitting atop Archaean gneisses, the laterite can be correlated with similar palaeosols that cover the 64 Ma Deccan flood basalts some 130 km to the north, yet they defy dating by palaeontological or radiometric means.  Dr Siffli would welcome offers to date the Sringeri lagerstätten (pusiffli@yahoo.com).

Chromium isotopes and Archaean impacts

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As mentioned several times in Earth Pages News, geologists have been slow to accept that the Earth’s evolution has been substantially affected by impacts of extraterrestrial bodies.  In hindsight, this stubborn scepticism seems perverse.  The discovery of impact-induced melt spherules in the Late Triassic sediments of SW England (see Britain’s own impact in EPN, December 2002) went almost unnoticed.  However, there is still an entrenched view that nothing really big has happened.  When similar spherule beds were reported from the Early Archaean greenstone belts in Australia and South Africa in 1986, and deduced to have formed by an impact, the authors were pounced on by those who thought they could plausibly explain the very odd rocks by unremarkable, Earthly processes. How satisfied Donald Lowe and Gary Byerly, of Stanford and Louisiana State Universities must be to find their view now proven beyond doubt, and to share in publishing the evidence.  The proof comes from isotopic studies of three spherule beds in the 3200 Ma-old Barberton greenstone belt in South Africa (Kyte, F.T. et al. 2003.  Early Archean spherule beds: Chromium isotopes confirm origin through multiple impacts of projectiles of carbonaceous chondrite type.  Geology, v. 31, p. 283-286).  Chromium isotopes in the rocks are so unearthly, that explaining them requires that they contain up to 60% of extraterrestrial material, probably from carbonaceous chondrite impactors.  Compared with the global spherule-bearing and iridium-rich K/T boundary layer (3 mm thick on average), that is the ejecta from the Chicxulub impact, the Barberton beds are much thicker (10-20 cm).  The authors estimate that, if the Barberton layers are globally representative, the impactor responsible for their formation could have been 50 to 300 times more massive than that which terminated the Mesozoic Era.  Besides that, three such layers formed within 20 Ma, and that suggests bombardment flux more than ten times that late in Earth evolution.

Triggering core formation at the microscopic level

Since Birch’s discovery in the 1950’s that the Earth’s excessive density compared with exposed rocks could be explained by a metallic, iron rich core, whose presence was detected by studies of seismic waves, there have been many explanations for core formation.  Some regarded the process as a slow accumulation of iron-rich melt as it sank from the mantle, others that it formed during Earth’s initial accretion from the iron-rich parents of metallic meteorites.  Lead and tungsten isotope studies indicate clearly that the core formed very early in Earth’s evolution, taking as little as 30 Ma.  However, for such a vast mass to have quickly segregated from the rest of the Earth poses awesome mechanical problems.  Alloys of iron, nickel and sulphur do have much lower melting temperatures than silicate minerals, and planetary accretion releases gravitational potential energy.  That serves to heat up a growing planet, but core-forming materials would melt long before the dominant silicates that envelop them, if indeed mantle materials did melt substantially.  So, at the centimetre scale of rocks, a melt fraction, however dense, would have to migrate and accumulate in globules with sufficient gravitational potential to sink through the viscous early mantle.  The boundaries of pores in which melts form are critical.  If the angles between silicate facets and melt-filled pores are large, tiny amounts of molten metal cannot become interconnected and migrate, unless the silicates begin to melt too or are actively deformed.  Since coexisting silicate and metal melts are not supported by geochemical evidence and deep planetary interiors are probably static, the fact that the interfacial angles of crystalline minerals are high poses quite a problem.  Geochemists at the University of Yokohama in Japan have performed complex experiments at high pressure and temperatures to simulate likely conditions during planetary accretion (Yoshino, T. et al. 2003.  Core formation in planetesimals triggered by permeable flow.  Nature, v. 422, p. 154-157).  They discovered that if metallic melts account for more than 5% by volume of the accreting body, then this melt can percolate through the solid rock, because the angles separating melt and solid fall below the critical value of 60º.

The implication is that even quite small planetesimals (>30 km radius) can quickly develop metallic cores, using energy released by the decay of short-lived isotopes that were plentiful early in Solar System history.  This is borne out by studies of metallic meteorites  Of course, the immense gravitational energy released by accretion of larger planetary bodies would result in the same differentiation, but if they formed by accumulation of smaller differentiated bodies there is no need to postulate within-planet processes on the microscopic scale.  The core would be “pre-manufactured”, only requiring blending of many smaller cores of accreting planetesimals

See also: Minarik, B. 2003.  The core of planet formation.  Nature, v.  422, p. 126-127.

“Greenhouse” gas website

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Dave Reay of the School of Geosciences at the University of Edinburgh has developed an extremely useful website that covers all the breaking news about “greenhouse” gases and climate change at www.ghgonline.org, which is easy to navigate and regularly updated.  It contains links to on-line publications and a comprehensive Links page.

Wars in the Congo and physical resources

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The Democratic Republic of Congo (DRC, formerly Zaire) is the most war-torn country in Africa, and has been since Belgium relinquished its largest colony in 1960.  It is also Africa’s most mineral-rich country outside of the Republic of South Africa.  Most of its population, particularly outside of the major cities, has been repeatedly caught up in the most savage conflicts, which have left more than 2 million dead and far more displaced or reduced to conditions of bare survival.  From the civil war following the attempted secession of the most mineral-rich province of Katanga shortly after independence to the present, Congo peoples’ suffering has centred on various groups’ attempts to loot its mineral riches.  Despite the DRCs  strategic importance as a supplier of cobalt and tantalum, for which it is the world’s largest source, and its world-ranking production of copper and zinc, diamonds (up to one third of a ton annually, mainly of industrial quality), and gold (up to 6 tons annually), neither the UN nor those powers currently engaged in Iraq have made any determined effort to end the 40-year plight of its people.

Every geologist suspects that war in the Congo has a direct link to its mineral resources, but until recently its economic basis has remained carefully hidden by the various warring groups, and to some extent by the world mineral industry which ultimately benefits.  Ingrid Samset of the University of Bergen in Norway has reviewed the particular role of diamonds in the recent phases of conflict, that followed the fall of the reviled President Mobutu in May 1997 (Samset, I. 2002.  Conflict of interests or interests in conflict?  Diamonds and war in the DRC.  Review of African Political Economy, v. 93-94, p. 463-480).

Following the occupation of eastern DRC by armies from Rwanda and Uganda in collusion with the anti-Kabila RCD forces, and the sending of troops by Namibia, Angola and Zimbabwe to assist the Kinshasa régime in mid 1998, official figures for production of and revenues from all physical resources fell far more dramatically than for other exportable commodities, such as coffee.  The largest falls involved diamonds and coltan (columbite-tantalite).  Both combine very high value relative to weight (coltan trades at up to US$400 per kilogram) with simple extraction technologies.  Both are mined extensively by artisanal groups, and so are attractive for quick, clandestine looting.  Tantalum is used in making capacitors, specifically for mobile phones, and the boom in the price of coltan followed the vast expansion of cellular phone networks world wide.   Zimbabwe, and to a lesser extent Angola and Namibia have won official concessions for diamond mining in exchange for their military involvement.  The embattled ZANU-PF régime in Harare is probably highly dependent on revenues from Congo diamonds.  In the case of Uganda and Rwanda’s involvement with opposition forces in eastern DRC, the economic aspects of their roles are more difficult to dig out.  Both countries lack diamond or coltan reserves, yet in the case of diamonds, their exports rose by 12 and 90 times, respectively, since the start of their involvement.  Comparing their export values with probable production in the area that they help control, there is a shortfall of about US$13.5 million.  Samset suggests that “missing” diamonds are being used directly as easily “laundered” barter goods in exchange for arms.  In the case of coltan, Rwanda is estimated to have benefited by US$250 million, at the time of the tantalum price peak in 1999-2000, from looting of eastern DRC.  Neither coltan nor diamonds carry signs of their origin (but see Forensic geochemistry to foil “fencing” of conflict diamonds in EPN, June 2002), so tracking looted goods and bringing those involved to account is no easy task.  The state of Israel is heavily involved in the gem diamond trade, as is the Republic of South Africa, and the USA accounted for more than 80% of all industrial diamond exports from the former Zaire.  One of the oddest coincidences was the sudden involvement in peace-making attempts during the Eritrea-Ethiopia war of 1998-2000 of the government of Rwanda, despite its geographic remoteness from that particular conflict and lack of diplomatic experience.

See also: http://www.american.edu/TED/ice/congo-coltan.htm for an analysis of the role of coltan in the DRC conflict.

Gut bacteria and human migration

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Our churning bowels and stomach mimic a variety of inorganic environments in which a large range of bacteria have thrived for hundreds, if not thousands of million years.  The stomach has low pH thanks to hydrochloric acid, sufficiently strong to make limestone fizz should you be unfortunate enough to throw up while collecting fossils.  Parts of the gut are highly reducing, so that humans contribute their bit to global warming through the action of our symbiotic methanogen bacteria, although much less so than ruminant mammals which are major methane producers.  We also host sulphate-sulphide reducing bacteria, with sometime spectacular effects in enclosed spaces.  The animal gut has been around for quite long enough for internal bacteria to evolve and adapt to the dietary habits of their hosts, mostly as symbionts.  However, some are pathogenic and infective.  One pathogen in particular is not infective, so its effects have remained undetected until recently.  It is now known that a major cause of gastric and duodenal ulcers, and digestive-tract cancers is the Gram-negative bacterium Helicobacter pylori.  Massive doses of acid suppressants and bactericides effect miraculous cures on individuals who have had decades of misery from stomach pain.  Now that the culprit has been fingered, you will not be surprised to learn that its DNA has been studied in some detail.  The results are surprising  (Falush, D. and 17 others 2003.  Traces of human migrations in Helicobacter pylori populations.  Science, v.  299, p. 1582-1585).  Helicobacter is extraordinarily diverse, and regionally distinctive.  Because it is pervasive, but not infective, the bacterium travels along with populations of its hosts, and is therefore a potential tool in tracking migrations.  There are 7 geographically distinct H. pylori groups today, and their genetic structure can be traced to ancestors in Africa, Central and East Asia.  Their geographic distribution matches those of human genetic and linguistic patterns, which have been attributed to the colonization of Polynesia and the Americas, to Neolithic migrations of agricultural peoples into Europe from the near-East, the expansion of Bantu-speaking people in Africa and to the slave trade.

Neanderthal review

The last ten years has seen enormous developments in understanding the first Europeans. So, a review of how they lived, how they differed from us, how they might have thought and how they came to an end shortly after our immediate ancestors turned up is very welcome (Klein, R.C. 2003.  Whither the Neanderthals?  Science, v.  299, p. 1525-1527)

The first volcanologists?

If there is ever a chance, the site that I would most like to visit is that discovered by Mary Leakey near Olduvai Gorge in Tanzania.  A bedding surface in volcanic ash records footprints of two adult australopithecines and a juvenile who trudged together through fresh debris from a nearby volcanic eruption.  The earliest and irrefutable confirmation of bipedalism, the tracks are also among the most poignant in the fossil record of humanity.  Did this family survive the tragedy?  The trackway is now covered to guard against erosion and theft.  Altogether less heart-rending are younger footprints in an ash layer from the Roccamonfina volcano in Italy (Mietto, P. et al. 2003.  Human footprints in Pleistocene volcanic ash.  Nature, v. 422, p. 133), long known to locals as “devils’ trails”.  The ash formed on the slopes of the volcano, as a pyroclastic flow, and the fossilised trail slopes at up to 80º.  Because the ash is about 350 thousand years old, whoever made the prints were not fully modern humans, but probably ancestors of Neanderthals (H. heidelbergensis).  The individuals had quite small feet, and may well have been children.  The tracks come down the slope, both zig-zagging and showing occasional hand prints to steady the descent.  They give the impression that whoever made them was not escaping an eruption, but having fun, much as kids today cannot resist hurling themselves down sand dunes and snow slopes.  There is another possibility: curiosity drove them up the volcano after products of an eruption had cooled.  Volcanologists cannot resist doing that either, and, as today, maybe they went up a little too early for comfort and had to leap for their lives.

See also:  Muir, H. 2003.  Earliest human footprints preserve prehistoric trek.  New Scientist, 15 March 2003, p. 15.

Earlier date for first suspected animals

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The earliest indisputable traces of metazoan animals are quite literally that – the impressions of soft-bodied organisms preserved as the Ediacaran fauna of Australian and other late-Neoproterozoic sediments dated around 565 Ma.  However, the profound differences in genetic make-up of existing animal phylla, which clearly at the time of the Cambrian Explosion, have been expressed as indicators of animals’ origins more than a billion years ago.  Consequently, the discovery in 1998 of what appeared to be non-Ediacaran trace fossils in the Neoproterozoic Vindhyan Supergroup of India triggered considerable interest.  The problem with many of India’s Precambrian sediments is their lack of precise and verifiable dates.  Occurrences of the sedimentary silicate glauconite in the Vindhyan prompted use of the K-Ar method, which suggested that they were pre-1100 Ma, but that is a notoriously unreliable technique.  Part of the lower Vindhyan succession contains poorcellanites that show textural evidence for having originated at ignimbrites, and they contain zircons of volcanic origin.  Once sampled, it was only a matter of time before precise single-zircon U-Pb dates became available.  In fact, two teams published simultaneously in the February issue of Geology, and gave similar ages from different places (Ray, J.S. et al. 2002.  U-Pb zircon dating and Sr isotope systematics of the Vindhayan Supregroup, India.  Geology, v. 30, p. 131-134;  Rasmussen, B. et al, 2002. 1.6 Ga U-Pb zircon ages for the Chorhat Sandstone, lower Vindhayan, India: Possible implications for early evolution of animals.  Geology, v. 30, p. 103-106).  The first paper gave an age of 1631 Ma for strata immediately beneath the supposedly fossiliferous formation, whereas the second bracketed it between 1628 and 1600 Ma for rocks beneath and above it.

If the structures preserved in the Chorhat Sandstone do prove to be true trace fossils, there will be little doubt that animals appeared at least three time earlier than the previous fossil-based estimate, more in line with the molecular evidence.  However, the structures are disputed, and there is another oddity about the palaeontology of the Vindhyan.  Limestones that conformably overly the 1600 Ma dated horizon have been reported to contain brachiopods and “small, shelly faunas” typical of the earliest Cambrian elsewhere.  Since the limestones are only a few hundred metres higher in the Vindhyan sequence, and contain 87Sr/86Sr isotope ratios that are appropriate for Neoproterozoic seawater, brings their content of Cambrian fossils into doubt.  Clearly, a great deal more work is needed to resolve the significance of the Vindhyan finds, particularly establishing accurate, basin-wide stratigraphic correlation.

Are mass extinctions artefacts of sampling bias?

Evidence for mass extinctions comes from inventories of fossil species, genera and families collected from the sedimentary record.  There has always been a geographic bias in this sampling towards more accessible areas and those with the greatest number of palaeontologists, i.e. towards rich countries.  Increasing grants for expeditions to remote areas and the slow growth in numbers of specialists in less well-endowed countries does smooth out the bias.  However, because of many factors, including ups and downs in sea level and the effects of orogeny on rates at which deformed sediments have been eroded, the stratigraphic record itself does not accurately represent time with exposed rocks.

The data on which extinction records rest are those compiled by the late Jack Sepkoski, yet until recently there has been little attempt to weight them according to stratigraphic record, although much statistical re-evaluation has gone on (e.g. The “Big Five” become the “Big Three”? Earth Pages of January 2002).  This stratigraphic evaluation to some extent pulls the rug from under those who speculate on the causality of extinction (Peters, S.E. and Foote, M.  2002.  Determinants of extinction in the fossil record.  Nature, v. 416, p. 420-424).  A great many ups and downs in the fossil record do seem to depend on the amount of exposed sedimentary rock.  Widespread gaps in the sedimentary record result in spurious and abrupt ends to evolutionary lineages; pseudo-extinctions.  Although the period- and era-ending extinctions seems still to be statistically valid, those at stage boundaries are suspect.  One of the lessons to be learned is that the previous good correlation between sea-level change and extinction and origination rates is particularly suspect, as eustasy is a first-order contributor to chages in sedimentary deposition and preservation.

Doubt cast on earliest bacterial fossils

In autumn 1996 two of the most blatant hyperboles in the recent history of the Earth sciences hit the world’s headlines; two groups of scientists, one from the USA, the other British, announced their discovery of fossil life forms in meteorites reputed to have originated on Mars.  The evidence was in the form of organised structures revealed by scanning electron microscopy.  Subsequently, most biologists and palaeontologists concluded that the case was, in the manner of the third possible verdict in Scottish courts, “not proven”.  Kindly scientists regarded the hype as being prematurely optimistic.  However, critical attention focussed on the announcements because they claimed first discovery of extraterrestrial life.  If one finds a mammoth while digging a ditch, there is some cause for celebration, and the world will believe and congratulate the finder, for the mammoth is unmistakable.  That is not the case for fossilized micro-organisms.  In 1993, William Schopf of UCLA, and co-workers, announced their discovery of the oldest known fossil bacteria in 3465 Ma cherts in a greenstone belt near Marble Bar in Western Australia.  They were microscopic wisps of carbonaceous material, that a trained eye might resolve into filaments made of bacterial cells.  Since the most common living filamentous bacteria are photosynthetic cyanobacteria, that bear close resemblance to sketches of the ancient structures, Schopf and colleagues performed the palaeontological equivalent of Aristotle’s syllogism, by declaring that indeed some of the structures were blue-green bacteria.  In what was generally regarded as an anoxic Archaean world, it seemed there were organisms working to oxygenate the environment.  Various lines of evidence, such as the isotopic composition of carbon in Archaean sediments, were later claimed by others to support such an early arrival of cyanobacteria, that eventually transformed the atmosphere and the conditions for life, so that oxygen-demanding Eucarya, such as ourselves, might evolve and diversify.

There is one snag with the Marble Bar chert.  It almost certainly formed by hydrothermal activity on the Archaean ocean floor; deep and dark.  Photosynthesis using solar energy would be unlikely.  Re-examination of the putative fossil filaments, using both microscope and Raman spectroscopy (means of estimating C/H ratios from spectra excited from carbonaceous matter by a laser) has raised a minor storm.  Martin Brazier of Oxford University and colleagues from Britain and Australia question the biological origin of the structures (Brazier, M.D. et al. 2002.  Questioning the evidence for Earth’s oldest fossils.  Nature, v. 416, p. 76-81).  Amazingly, one of their observation while examining Schopf’s original material with a high powered microscope was that by racking the objective up and down to visualize the structures in 3-D, most showed to be highly irregular smears of carbonaceous stuff.  Only one position provided life-like shapes.  While Brazier et al. do not deny that life was around in the chert-forming hot spring – probably chemautotrophic prokaryotes – they are convinced that Schopf’s structures are artefacts formed by hydrothermal reworking of degraded organic molecules.  In a rejoinder, Schopf and US colleagues accept the deep-water, hydrothermal origin of the cherts and concede that none of the structures are blue-green bacterial cells, but still maintain that they are biogenic (Schopf, J.W. et al. 2002.  Laser-Raman imagery of Earth’s earliest fossils.  Nature, v. 416, p. 73-76).  The earliest undisputed fossil micro-organisms are almost 1.4 billion years younger than those of Marble Bar.  They are from cherty layers in banded iron formations, formed probably in shallow water by the combination of oxygen produced by cyanobacteria with dissolved ferrous iron.  The Archaean contains plenty of BIFs, and perhaps a search for the oldest biotas in them would give more definite results.

See also:  Kerr, R.A. 2002.  Earliest signs of life just oddly shaped crud?  Science, v. 295. P. 1812-1813.

Antarctic melting and northern hemisphere deglaciation

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There is a large body of opinion, supported by plenty of circumstantial evidence, that the end of the last glacial maximum around 20 ka was controlled by processes that operated in the North Atlantic and its seaboard.  A favoured mechanism is the re-establishment of thermohaline circulation involving North Atlantic deep water that dragged surface water northwards from the tropics, to set up the Gulf Stream.  Temporary shut-down of thermohaline flux, probably by massive release of freshwater to the North Atlantic from melting of ice sheets, is widely understood to have triggered the sudden reversal to frigid conditions in the Younger Dryas around 11.5 ka.  The largest warming pulse in the northern hemisphere, between 14.6 to 14.0 ka, is recorded by a sudden increase in d18O of ice in the Greenland cores, and is known as the Bølling-Allerød warm interval.  Around that time, sea level rose by 20 m in a few hundred years, and that involved production of fresh glacial meltwater at a rate equivalent to the continual flow of five rivers the size of the Amazon.  Such rapid sea-level rise drowned coastlines and in some areas killed coral reefs.  On such drowned reef in the Caribbean gave a date of 14.2 ka, which since 1989 has been the only indicator of precise timing for the massive influx of meltwater to the oceans.  The date is within the Bølling-Allerød, hence the link between warming and events around the North Atlantic.  That central hypothesis is now under threat, following the dating of drowned coral reefs on the Sunda Shelf at 14.7 ka, and a re-evaluation of the Caribbean data. (Weaver, A.J. et al. 2003.  Meltwater pulse 1A from Antarctica as a trigger of the Bølling-Allerød warm interval.  Science, v. 299, p. 1709-1713).

Using the revised ages and climate modelling, Andrew Weaver and colleagues from the Universities of Victoria and Toronto, Canada and Oregon State University see the massive ice-melting as the precursor to the Bølling-Allerød warm interval and deglaciation of lands around the North Atlantic.  A more plausible source of freshwater influx is a major melting event in Antarctica, so warming in the south may well have driven that of the northern hemisphere.

See also: Kerr, R.A. 2003.  Who pushed whom out of the last ice age.  Science, v. 299, p. 1645.

Digital library of educational web sites

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The Digital Library for Earth Systems Education now has a site that can act as a gateway to thousands of Earth Science web sites that provide educational materials from school to professional level (www.dlese.org) .  There is a comprehensive range of topics, and a potentially useful enhancement is part which announces conferences and discussion groups.

Devonian art

The Devonian Period witnessed sudden diversification of vertebrate animals, including the first amphibians.  The oceans were teeming with other life forms.  Museums have for a long while commissioned artists to create dioramas of ancient seas that express part of their diversity.  Using gaming software, British artist Christian Darkin is in the process of developing an interactive Devonian diorama, eventually intended for museum use.  His work in progress can be viewed at   www.geocities.com/christiandarki/fish.htm .  You will need the Macromedia Shockwave plug in, downloadable direct from Darkin’s site, and a higher speed connection than with a normal modem.  However, the experience is dramatic and informative.

Silica in BIFs

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Following close on the heels of the hypothesis that iron in Precambrian banded iron formations was precipitated by bacteria (see BIFs and bacteria in February 2003 issue of Earth Pages News) is an account of the origin of silica that makes up roughly half the banding (Hamade, T. and 4 others 2003.  Using Ge/Si ratios to decouple iron and silica fluxes in Precambrian banded iron formation.  Geology, v. 31, p. 35-38).  The rare-earth elements and Nd isotopes in the iron-rich layers suggests that they probably originate from ocean-floor hydrothermal activity.  How their cherty layers formed has largely been overlooked.  Before the Cambrian Explosion there were no organisms that secreted silica in their skeletons.  Consequently, the dissolved silica content of Precambrian oceans was probably much higher than now.  Because silica becomes highly soluble only under very alkaline conditions, it may have been close to saturation in Precambrian seawater.  Quite small changes in seawater chemistry would result in its precipitation as fine-grained chert.  But the main issue is where the dissolved silica came from.

Hamade et al. examined the amount of germanium in the cherts, because it is in the same group of elements and acts as if it were a heavy isotope of silicon.  So it follows Si very closely in its distribution.  Alteration of mafic rocks by sea-floor hydrothermal activity dissolves Si, and so does weathering of continental materials; there is a dual source of seawater Si.  However, basalts have more than 10 times as much Ge as do granitic rocks, and the Ge/Si ratio is a good guide to the dominant source of Si.  Cherts in the BIFs from the famous Hamersley basin in Western Australia have Ge/Si ratios that increase with the amount of iron.  The most silica-rich BIFs seem to have formed from waters derived from continental areas, whereas the iron-rich varieties have a sea-floor hydrothermal signature.  The authors conclude that these BIFs formed on a continental shelf subject to regular, periodic upwellings of deep ocean water.

When did southern Tibet get so high?

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For about a decade it has been suggested that the Tibetan Plateau, which rises to more than 5000 metres, has a profound effect on climate.  This may be partly due to the way such a high and enormous area deflects regional wind patterns, but largely to its profound interconnection with the South Asian monsoon.  When such a circulation barrier arose is critical to understanding how it relates to climate evolution in the latter part of the Cenozoic.  There are various suggestions, based on aspects of its structural and magmatic evolution.  Theory suggests that the southern part came into being in Eocene times, possibly because a segment of the lithosphere beneath broke off to subside into the mantle – there are volcanic rocks whose chemistry does suggest such a mechanism.  About 8 Ma ago the southern Plateau began to spread laterally, producing a series of N-S extensional basins, which suggests that by then sufficient gravitational potential had accumulated to make the thickened crust unstable.  About that time various signatures arose in foraminifera of the Indian Ocean and sediments derived by erosion, which suggest that the monsoon increased in intensity.

When the Plateau attained sufficient elevation above sea level to start spreading sideways and affect atmospheric circulation largely rests on these theoretical judgements.  For the ideas to firm up needs some means of estimating topographic elevation, which is not easy to do.  One way is to use plant remains that can give clues, either because the species involved are sensitive to elevation today, or the morphology of their leaves shows signs of physiological adaptation to elevation.  The first is ruled out in old sediments, simply because the species present are now extinct..  Plants metabolism is dependent on diffusion of water and CO2 into their leaves during photosynthesis, and features, such as stomata density, give clues to the conditions for such diffusion.  Luckily, sediments from southern Tibet do contain well-preserved plants, and a multinational group led by Bob Spicer of the British Open University have attempted to assess palaeo-elevation for the time at which they were deposited (Spicer, R.A. and 7 others 2003.  Constant elevation of southern Tibet over the last 15 million years.  Nature, v. 421, p. 622-624).  Their method relies on linking leaf morphology to a property of the atmosphere, known as moist static energy (MSE), through estimates of atmospheric enthalpy from the leaves.  That is not the end of the estimation, because MSE needs to be related to elevation and the only way is to use climatic modelling for the past.  Whatever, Spicer and colleagues reckon that 15 Ma ago their sampling site was more or less at the same elevation as today, around 4.5 km above sea level.  If true, they have established that the south part of the Plateau was already in existence during the Middle Miocene.  Being so convoluted, despite its apparent precision, the leaf analysis method does need independent confirmation.  There is a much easier and arguably more reliable method, based on the change in the size of bubbles formed by gas escaping from lavas, according to atmospheric pressure (see Cunning means of estimating uplift in November 2002 issue of Earth Pages News).  There are lavas in southern Tibet that date from Cretaceous times, including some about a million years younger than the plant remains.

Precambrian warmth and methane

Methane is a more efficient “greenhouse” gas than CO2, but it soon oxidises in the presence of oxygen.  During the Phanerozoic there have been several massive releases of methane, probably from gas hydrates in deep-ocean sediments, which produced warming spikes that decayed away quickly in geological terms.  Before there was much, if any, oxygen in the atmosphere, methane could linger and add to the retention of heat by carbon dioxide and water in the atmosphere.  One of the longest running disputes in environmental geochemistry concerns when oxygen levels became significant in the Precambrian, and what they were compared with later times.  Whether the Earth was warm or cold has a bearing on this.  Cosmological theory suggest that stars similar to the Sun progressively grow more energetic with time.  Without some kind of greenhouse effect, the Earth would have been condemned to frigidity from its outset.  Even today, with a more radiant Sun, only atmospheric retention of solar heat keeps overall temperature from being well below freezing.  The further back in time, the greater the “greenhouse” effect would have to have been to stave off complete ice cover and a runaway “icehouse”.  Methane almost certainly played a part in this once methane generating organisms evolved, up to about 2200 Ma, when there are signs (continental redbeds and soils rich in iron oxides) that atmospheric oxygen was appreciable.  However, warmth prevailed for about 1.5 billion years thereafter, until the plunges into frigid conditions of the so-called “Snowball Earth” period from about 700 to 550 Ma.  Somehow, the greenhouse effect lingered.

Alexander Pavlov of the University of Colorado, and colleagues from Pennsylvania State University have addressed the implications of this continued warmth in terms of maximum oxygen levels needed to avoid complete oxidation of methane releases (Pavlov, A.A. et al. 2003.  Methane-rich Proterozoic atmosphere?  Geology, v. 31, p. 87-90).  Today, more than 90% of all methane production beneath the ocean floor is consumed by bacteria, depending on the amount of dissolved oxygen and sulphate ions (for aerobic and anaerobic methanotrophs).  There is plenty of evidence that deep Precambrian ocean water was anoxic, so a great deal more methane would have emerged from them.  That it was also poor in sulphate ions is shown by their low levels in solid solution with carbonates and Proterozoic sulphur isotopes in marine sediments.  The authors argue that this signifies low atmospheric oxygen levels, around 5 to 18 percent of modern concentrations.  The scene may have been set for an excess of methane production over its oxidation, thereby keeping the “greenhouse” warming above the levels when glaciation would have been widespread..  If so, something completely upset this balancing act in the Neoproterozoic, to drive down temperatures several times – the “Snowball Earth” events.  The trigger may have been a boost in oxygen production and retention in the atmosphere.

El Niño in the Eocene

The oceanographic-climatic phenomenon in the equatorial Pacific, known as the El Niño-Southern Oscillation (ENSO), now seems to be major force in driving climate shifts far afield, such as the current drought in the Horn of Africa.  Its cyclicity relieves the suffering brought by El Niño events, yet the processes may well be highly unstable.  Some believe that it is only a matter of time before ENSO reverts to a permanent El Niño condition, with disastrous consequences.  Such a stabilisation in the past may have resulted in warming at high latitudes that permitted lush vegetation in near-polar regions, during the Cretaceous and the Eocene.  The Eocene was much warmer than now, as a result of a massive release of methane from seafloor sediments around 55 Ma.  So it makes sense to look at its climate record to check for a permanent El Niño.  Matthew Huber and Rodrigo Caballero of the University of Copenhagen have compared climate records from annually layered lake sediments from the Eocene of Germany and Wyoming in the western USA with climate models to test the hypothesis (Huber, M. & Caballero, R. 2003.  Eocene El Niño: Evidence for robust tropical dynamics in the “hothouse”.  Science, v. 299, p. 877-881).  The climate data from the lake sediments (thickness variations in annual layers) show clear signs of a roughly 5-year cycle of climate change, attributed to an Eocene ENSO.  This tallies nicely with simulations for the Eocene continent-ocean set-up.  Although the authors claim that their findings refute the hypothesis that global warming tends to shut down ENSO, which is a comforting thought, Eocene ocean and air circulation was not the same as now by any means.  There have been interglacial periods during the Pliocene to present climate system in which temperatures exceeded those of the Holocene.  Surely, annually layered sediments from those times will provide a better test.

Letting Cameroon’s soda-pop lakes go flat

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The April 2001 issue of Earth Pages News (Taming Lake Nyos, Cameroon) announced attempts to release CO2-rich water from the bottom of the notorious Lake Nyos, by setting in motion a sort of soda siphon.  A massive discharge of gas from Lake Nyos in 1986 killed 1700 local people, possibly after a small earthquake and landslide disturbed the bottom water.  Nearby Lake Monoun had already asphyxiated 37 people two years previously.  Both lakes are stagnant, and carbon dioxide released by exhalation from deep magma chambers dissolves under pressure in their deepest levels.  If the water rises, then it belches out dissolved gas, with potentially disastrous results.  Taming these killer lakes by bringing gas-rich water up pipes works because as the gas bubbles out of solution it rushes up the pipe dragging water with it, to create a fountain.  This is slowly relieving the danger of Lake Nyos, and there have been no problems caused by disturbing the deep water by the pipe’s presence, so far.  A French team from the University of Savoie is now installing a similar device in Lake Monoun, which poses a greater threat than Nyos, because the gas-rich water is only 60 metres down.  Potentially far more dangerous are the lakes of the East African Rift system, where magma exhalation is far more widespread and seismicity more common.  Lake Kivu, near Goma on the border between Rwanda and the Democratic Republic of Congo, threatens far more people with a massively greater threat, which also includes huge volumes of buried methane.  Luckily, the lava flow there during early 2002 did not reach the gas-rich level.  The experience from Cameroon promises an eventually easing of the dangers elsewhere.

Source: Krajick, K. 2003.  Efforts to tame second African “killer lake” begin.  Science, v. 299, p. 805.

Hydrogeology of sea-floor cooling

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Much of the Earth’s internal heat production escapes from the ocean floor, by a combination of direct cooling of new lavas at ridges, hydrothermal pumping of seawater through oceanic crust and conduction.  These processes are responsible for the increase in density of oceanic lithosphere that causes the ocean floor to gradually deepen away from spreading axes, thereby adding a gravitational force (ridge-slide force) to help drive plate tectonics.  The cooling also ensures that oceanic lithosphere is sufficiently cool at destructive margins for metamorphic processes in subduction zones to increase its density above that of the mantle, thereby largely driving plate tectonics through slab-pull force.  More than 70% of internal heat loss through the oceans is dissipated through crust that is younger than 1 Ma.  Much of that emanates from huge hydrothermal geysers, about which a great deal has been revealed in recent years.  What of the other 30% that escapes through older crust?  The older it is, the more it is literally blanketed by sediments that should act to block circulation of seawater, because they are so fine grained and impermeable.  It might seem as if heat lost would have to be by conduction alone.  That is not sufficient to explain the shape of the ocean basins.  However, some recent work near the Juan de Fuca Ridge in the NE Pacific by a team from the USA, Canada and Germany (Fisher, A.T. and 12 others 2003.  Hydrothermal recharge and discharge across 50 km guided by seamounts on a young ride flank.  Nature, v. 421, p. 618-621) shows that basic principles of hydrogeology guide seawater to increase heat loss.  Outflow is not through the sedimentary cover, but through seamounts, which are outcrops of the underlying igneous part of the crust.  Like many springs on land, the water that flows from them can come from far afield.  The sedimentary cover acts as an aquiclude, making the crystalline crust a confined aquifer, but for any flow to operate water must infiltrate the ocean floor.  Fisher and colleagues have found that some seamounts have higher heat flow than others, and are sites of outflowing warm water.  Some have anomalously low heat flow and may well be sites where seawater is infiltrating.  Dating outflowing water using 14C reveals that it is very young, and must have flowed rapidly, yet in their study area there are no signs of significant recharge through the sediments.  One seamount, 50 km from another which discharges water is the only likely source.  So, it seems as if the distribution and number of sea mounts on the oceanic part of a plate might bear greatly on the processes that eventually take place when the plate is subducted.  “Pimply” plates could have cooled more than smooth plates with an unbroken blanket of inefficiently conductive sediments.

Young age for “Mungo Man”

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In the February 2001 issue of Earth Pages news, I commented on the extraordinary feat of Australian geneticists’ having extracted mitochondrial DNA from fossil Australians that date back perhaps 60 thousand years (Out of Africa hypothesis confounded?). The oldest not only represents the earliest Australian yet found, but turned out to be very different from that of later inhabitants (Adcock, G.L. et al. 2001.  Mitochondrial DNA sequences in ancient Australians: Implications for modern human origins.  Proceedings of the National Academy of Sciences, v. 98, p. 537-542).  That was “Mungo Man”, named after an archaeological site near Lake Mungo in western New South Wales.  At the time of publication, the date associated with the level in which the skeleton had been found was about 60 ka).  This was so early relative to the evidence for a 70 ka estimated age for the last common male ancestor of DNA in modern humans’ Y chromosomes (one pin in the Out of Africa Hypothesis), that multi-regionalists reckoned that it supported their ideas.  Oddly, the dating, based on thermoluminiscence of quartz, which records the time since grains were last exposed to daylight, used material from 400 metres away from the burial.

In the last few years, thermoluminescence dating has improved.  Using an optically stimulated variant to date sand grains from Mungo Man’s burial, James Bowler and associates from Australia have resolved the problem (Bowler, J.M. and 6 others 2003.  New ages for human occupation and climatic change at Lake Mungo, Australia.  Nature, v. 421, p. 837-840).  The burial was 40 ka ago, late enough for migrations spreading from Africa around 70 ka to have reached Australia.  Bowler and colleagues suggest that first colonisation of Australia was perhaps around 50 ka.  The date also support two other much debated ideas, that humans’ arrival resulted in their eating to extinction most of the large animal species in Australia, and by using scrub burning on a large scale to drive game in the “red centre”, changed the climate to its present arid state.  Mind you, climate change may have been coincidental and arose from global cooling and low-latitude drying as northern ice sheets began to spread in earnest.  Possibly climatic stress drove the first Australians to adopt fire as a hunting tool.  What the new work does not do is set to rest the suspicions for even earlier occupation recorded by artefacts and even stone markings that may be art.  Some workers have suggested that these may date to more than 100 ka, although without a clue as to the creators.

See also:  Young, E. 2003.  Mungo Man has his say on Australia’s first humans.  New Scientist, 22 February 2003, p. 15. 

Darwinian evolution of humans challenged by Y-chromosome data?

This section is usually reserved for items that predate historic times.  However, new work on genetic markers in the Y-chromosomes of Central Asian (from the Pacific to the Caspian Sea) men has revealed an astonishing feature.  Of the 2123 individuals who donated swabbed tissue for Y-chromosome DNA sequencing 8% have almost identical patterns of markers.  Scaled up to the regional population, the data suggest that about 16 million men in the area show this peculiar similarity – about 0.5 % of all living males.  The authors of the study (based in Mongolia, Uzbekistan, China, the UK and Italy) make a strong case for the direct male lineage of this living population having started in Mongolia 1000 years ago, and really getting underway with Genghis Khan’s imperial exploits in the 13th century (Zerjal, T and 22 Others 2003.  The genetic legacy of the Mongols.  American Journal of Human Genetics, v. 72, p. 717-722).  For the line to have remained so dominant requires “social engineering” on an almost superhuman scale.  Not only must Genghis himself have been the “stud” he is reputed to have been, together with his contemporary, close male relatives and their direct male descendants, but unrelated men of the time in that region must somehow have been excluded from access to local women.  History suggests that was ensured by massacre and bondage on a vast scale throughout the history of the Mongol Empire.

Markers in Y-chromosome DNA arise through mutation, and are highly unlikely to carry any kind of genetically determined trait, least of all a predilection for pillage, murder and rape!  Complex analysis of the distribution of genetic markers in populations leads to ideas about how they arose, their relatedness to other markers, and an estimate of their age relative to one another.  Study of Y-chromosome markers helps understand when a male lineage began.  One such marker is estimated to have first appeared about 70 thousand years ago (see Eve never met Adam in Earth Pages News, November 2000) and occurs in all analysed modern men, giving rise to the notion of a last common male ancestor living around that time.  That all modern males are descended from him suggested some kind of evolutionary “bottleneck” at that time, through which only a very small, related group’s were fit, in the Darwinian sense, to pass.  Maybe some other mutations conferred that fitness.  Perhaps some universal calamity reduced human population to only one or two small bands; chance rather than genetic determinism..  The third suggestion was that a small group’s development of a new technology conferred the potential for them to have progeny that survived to breed successfully for generation after generation, thereby coming to dominate the small populations of the pre-agricultural period.  The last would have had little to do with Darwinism, arising from a cultural change that had a dramatic effect.  The Genghis-related Y-chromosome discovery raises another possibility, that of social and sexual dominance of some “Big Man” through political achievement and ruthlessness; aspects of conscious social being and culture, and indeed economics and technology.  Tool makers and users who passed their skills down the generations are quintessentially human, and have increasingly developed with a cultural “cushion” from purely unconscious, natural processes for 2.5 million years.  Surely, some kind of “Big Man” (and possibly “Big Woman”) hypothesis has a place in thinking about human evolution as a whole.

The Early Cretaceous lagerstätten of NE China

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Barely a month passes without some weird fossil emerging from the widespread excavations in Early Cretaceous lacustrine sediments of north-east China.  It is probably the most productive palaeontological formation in the world, and has shed light on more than just the dinosaurian origin of birds, and rives ideas on the rise of angiosperm plants and early mammals.  As well as abundant fossils, the lagerstätten formed under low-oxygen conditions and preserves exquisite detail of soft tissue.  A review of the material and the environment in which it formed is welcomed by all palaeontologists (Zhou, Z, Barrett, P.M. & Hilton, J. 2003.  An exceptionally preserved Lower Cretaceous ecosystem.  Nature, v. 421, p. 807-814).  Zhou et al. Discuss the formation from two angles.  Scientifically their focus is on the potential for building a complete ecosystem for the area during the Early Cretaceous.  However, they also record the massive problems that result from haphazard collection by organised teams of locals and fossil dealers – incidentally the source of the infamous Archaeoraptor forgery (see “Piltdown” bird, in March 2001 issue of Earth Pages News).  Their review is also a plea for some kind of firm regulation of collection, although experience from many other lagerstätten suggests that is unlikely in the short-term.

Did terrestrial life emerge later than geochemists think?

A lot hangs on the notion that life can make it from abiogenic chemistry very quickly once a world has watery seas.  Evidence from oxygen isotopes in the oldest known terrestrial zircons suggests that liquid water was around on Earth by about 4400 Ma (see Pushing back the “vestige of a beginning” in Earth Pages News of February 2001, and The Hadean was cool June 2002).  It lies behind the search for signs of life on Mars and the fiasco surrounding the premature announcement of bacterial fossils in a meteorite reputedly from the Red Planet.  Right here, controversy has been raging over the once-living status of tiny patterns in 3500 Ma cherts from Western Australia (see Doubt cast on earliest bacterial fossils in Earth Pages News, April 2002), and on the true significance of isotopically light carbon trapped in apatite crystals in the 3800 ma Akilia metasediments of West Greenland.  Both have been claimed as signs of early, well-organised life, but the evidence is circumstantial.

Investigative journalism is very welcome in science, mainly because most scientists are either too polite, or grumble quietly in the coffee room.  Jon Copley, who teaches at Southampton University, has ventured into the field by interviewing some of the main antagonists in the “Is this a sign of life” debate (Copley, J. 2003.  Proof of life.  New Scientist, 22 February 2003, p. 28-31).  His article is most revealing, by getting down to brass tacks.  There is a lazy tendency in science to invoke William of Ockham’s “Razor”, i.e. that the simplest explanation of data is the best.  That is fine for the Old Bailey, in the manner of Roman legal argument of cui bono (who benefits?), but the natural world has a cussed tendency to pay no attention to human linear thought,  It is not a place for “elegance”, no matter how much scientists feel in awe of elegant mathematical proofs.  That it is wielded in favour of the most complex process in the universe to account for geochemical and other data is a bit odd.  Central to Copley’s sharp journalism lies something of which C-isotope specialists do not speak much.  At temperatures around 400ºC and a few hundred times atmospheric pressure can result in carbon monoxide and hydrogen combining to form hydrocarbons.  Fischer-Tropsch synthesis of hydrocarbons that fuelled Nazi Germany and South Africa under apartheid does occur in nature.  The ideal place is around deep-sea hydrothermal vents.  The reactions favour 12C over the heavier 13C and results in d13C just as negative as do living processes.  Isotopically light carbon in rocks that do not contain cast iron confirmation through tiny fossils, cannot be seen as proof that life existed.  Probably the oldest irrefutable fossils are of bacteria in the 1900 Ma Gunflint Chert of Ontario.  If we cannot be sure that C-isotopes help detect living processes on the early Earth, then results from missions, such as Beagle-2, to Mars could be exercises in futility.

Freezing the Antarctic

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Records of seawater oxygen isotopes and its Ca/Mg ratio shows that a substantial permanent ice sheet first formed in Antarctica in the Oligocene Epoch, about 34 Ma ago.  The favoured explanation, until this month, was that the South polar continent became thermally isolated from the rest of the planet when circumpolar currents were able to flow around it, once South America and Australia had separated from Antarctica and opened the “gateways” of the Drake and Tasmanian Passages.  But what if atmospheric CO2 played a role?  A drop in the “greenhouse” effect and global cooling could have driven polar temperatures low enough for ice formation without an oceanographic influence.  Once established, the albedo effect of a large ice sheet would seal Antarctica into permanent freeze-up.  Factoring all the likely components in a general circulation model leads to a surprise (DeConto, R.M. & Pollard, D. 2003.  Rapid Cenozoic glaciation of Antarctica by declining atmospheric CO2, Nature, v. 421, p. 245-249).  The opening of the Drake and Tasmanian Passages was not accompanied by a sufficient depth of water to support massive current reorganisation until several million years after the ice cap left its clear imprint on the marine record.  DeConto and Pollard’s model shows that even with closed Passages an ice cap would have formed, if CO2 levels had fallen below three times those that prevailed in the Holocene, before industrial emissions began.  Global cooling had begun somewhat earlier than Antarctic freeze-up, following the high around the Palaeocene/Eocene boundary (~55 Ma), falling to a plateau about 40 Ma ago.  Undoubtedly CO2 concentrations had fallen globally for this to have happened.  Of course, there is no Oligocene ice, from which glaciologists might extract trapped bubbles and samples of ancient air with which to refute or confirm the model.  However, a decrease in carbon dioxide would also cause the acidity of rainfall to decrease as well as the amount of rainfall globally, and that might show up in changed weathering processes, especially in the tropics of the time. 

How patterned ground forms

Visiting flat areas of permanently frozen ground brings you face to face with truly bizarre patterns at the ground surface.  Some are perfect hexagons of stones around finer soils, others doughnut-like circles and then a perplexing range of other features that look for all the world as though they were built by humans.  Undoubtedly, they result from the forces at work when the top soil layer freezes and thaws annually, together with soil creep down extremely shallow slopes, repeated over millennia.  However, exactly how the patterned ground develops has eluded geomorphologists for more than a century.  Rejecting the reductionist approach that any landform’s evolution can be deduced from basic principles of physics seems to be the key (Kessler, M.A. & Werner, B.T. 2003.  Self-organization of sorted patterned ground. Science, v. 299, p. 380-383).  Kessler and Werner of the University of California modelled the two likely processes of ice lensing that sorts stones and finer soil, and the transport of individual stones along the lines of accumulated stones as freezing fines expand, building in elements of spatial and time scales plus other parameters such as surface slope.  Their model is self-organising, and proceeds to mimic many of the intricacies of patterned ground, even the most labyrinthine.  It might seem a little heavy handed to crunch numbers to help explain what are really quite minor features.  But having demonstrated the power of non-linear modelling here, the authors open up a novel approach to landscape evolution of every scale and antiquity.

Carbon dioxide and Martian channels

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Despite the evidence from the neutron detector on Mars Odyssey for the possible existence of subsurface water on Mars (Water on Mars, August 2002 Earth Pages News) not everyone accepts that minor rills and channels on its surface are due to periodic melting of buried water ice (Water on Mars, July 2000Earth Pages News).  Two small pieces in New Scientist contest that view.  In a letter, Wytse Sikkema of Shell likens them to features carved by turbidity flows (suspensions of solid particles in a fluid, such as avalanches, ash flows and submarine turbidity currents) which they resemble more than stream channels (Sikkema, W. 2003.  Rivers of Dust.  New Scientist, 18 January 2003, p. 24).  Sikkema suggests that the supposed ocean-like basins on the Red Planet are filled with dusts carried by such flows.  Support for such a mechanism emerges from observations of gullying in progress during Mars’ late spring near the poles, when temperatures were too low for liquid water to exist.  Nick Hoffman of the University of Melbourne, suggests that the active gullying that he observed  on successive Mars Global Surveyor images involves rapid vaporisation of CO2 snow and ice to lubricate dust avalanches (Nowack, R. 2003.  Ravines hint at gas avalanches on Mars.  New Scientist, 18 January 2003, p. 14-15).  Hoffman also considers that massive release of gas by boiling of buried CO2 liquid could have carved the much larger valley systems on Mars by massive flows of dust-gas mixtures.  If he is correct, there is no reason to consider Mars either as a haven for early life or one for intrepid astronauts.  Britain’s Beagle 2 probe and two unnamed NASA Mars rovers, due for launch this year, should resolve the issue, but if water is not confirmed, there will be huge disappointment for both teams involved with those missions.

Frightened by impacts?

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If so, the site to visit is at NASA’s Jet Propulsion Laboratory ( www.jpl.nasa.gov/temlates/flash/neo/neo.htm ).  The Near Earth Objects team has designed the site for general education about the kinds of space chunks that might strike, the risks involved and what will probably happen when we get very unlucky.

The chemical conditions for life

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Robert Williams (Oxford University) and João Fraústo da Silva (Technical University of Lisbon) have an unconventional, but plausible take on the conditions for life’s origin and evolution (Williams, R.J.P & Fraústo da Silva J.J.R. 2003.  Evolution was Chemically Constrained.  Journal of Theoretical Biology, v. 220, p. 323-343).  However life began, presumably as cytoplasm containing DNA, RNA and proteins within a semi-permeable wall, it was surrounded by the chemistry of whatever environment it appeared in.  The proto-cell would have drawn hydrogen ions from water, to perform the proton pumping that is essential to all living organisms, and thereby created more oxidising conditions in its immediate vicinity.  Oxidation would have generated nitrogen from ammonia, released metals from their sulphides and converted other sulphides to sulphates.  Conversely, ions in its surroundings would have been able to “leak” into the cell itself.  By creating oxidised radicals, this inward leakage would have rebounded the cell’s activity on itself, with potentially toxic consequences.  Survival depended on two things: exploiting the opportunities, such as nitrogen fixation, using oxygen and even photosynthetic chemistry; and fending off potential toxic shock.  One of the most interesting aspects is the role assumed by calcium ions.  Their presence inside a cell would have precipitated DNA, by binding to it, with fatal consequences.  The upshot, according to Williams and Fraústo da Silva, is the special role of calcium as a messenger ion, perhaps having arisen through the necessity to pump it out again.  Today, the range of calcium concentrations in cells is extremely limited; too much or too little being fatal.  Perhaps a sudden change in the calcium-ion concentration in seawater in the late Neoproterozoic was responsible for the extreme excursions in carbon isotopes that are ascribed to mass extinction and equally massive adaptive radiations.  My own stab in the dark, is that a protective response to calcium stress by metazoans at that time may explain the sudden appearance of calcium-rich hard parts, which we know as the Cambrian Explosion.  They evolved means of excreting calcium from their many cells, so creating an outer “shell” that eventually developed into “armour” or “armament”.

The delightful aspect of Williams and Fraústo da Silva’s ideas is that they break from pure genetic determinism and the dominance of pure chance in addressing the central issue in the whole of science – the complete interconnectedness of real nature.

Archaean tectonics was different

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Higher mantle heat production in the past suggests that at some stage in the evolution of plate tectonics oceanic lithosphere would arrive at destructive margins too hot for oceanic basalt to dehydrate and form eclogite.  Without excess density over that of the mantle, conferred by subducted eclogite (3300 kg m-3), the lithospheric slab would descend at a shallow angle, oceanic crust would probably undergo wet partial melting, and maybe slab pull force would be so low that subduction was a hit or miss affair.  The thermal state of the Archaean Earth might not have had plate tectonics as we know it today.  However, studies of the oldest probable ocean floor (the >3800Ma Akilia Association of West Greenland) looks for all the world as if it formed as an accretionary prism as a result of normal-seeming plate forces.  Previous speculation about Archaean tectonics assumed basaltic oceanic crust, much like today’s.  High heat production also implies that Archaean constructive margins generated a great deal more magma by partial melting of mantle with higher potential temperature; probably more magnesian, picritic primary magma (Foley, S.F et al. 2003.  Evolution of the Archaean crust by delamination and shallow subduction.  Nature, v. 421, p. 249-252).  Instead of the lower oceanic crust being made from gabbroic cumulates, it was then probably dominated by ultramafic products of fractional crystallization.  Foley, and colleagues Stephan Buhre and Dorrit Jacob of the Universities of Greifswald and Franfurt in Germany, show from high-pressure experiments that such lower crust would form dense pyroxenites.  At destructive margins these might delaminate from the upper oceanic crust to subduct steeply, thereby conferring slab-pull force to drive tectonics.  Their eventual partial melting would source basaltic magmas to add to older oceanic crust that failed to subduct during the earliest Hadean times.  That would explain the lack of continental materials older than 4000 Ma.  .  The partial melting of garnet-bearing mafic materials (probably garnet amphibolite) that sourced Archaean continental crust would have had to await the end of such delamination, when the whole oceanic crust could descend, albeit with hot wet basalt in the upper part of the slab.  Interesting though the ideas in the paper are, apart from the authors suggestion of a connection with element depletion of the upper mantle progressively affecting an ever deeper zone, they hark back to thoughts on Archaean processes as early as the late 1970s.

Eskola’s mantled gneiss domes revisited

The Finnish geologist Pentti Eskola famously recognised in the 1940s that many basement terrains throughout the world, particularly in Scandinavia, have large tracts of gneiss in the form of domal structures separated by synforms (mantles to the domes) of supracrustal rocks.  These mantled domes give a curious “egg-box” appearance to the geology of many shield areas, usually picked out by the conventional pink colours used to signify granitic rocks and greens for supracrustal belts.  Once it was recognised that interference between upright folds of different ages and with different axial trends could produce “egg-box” structures on the outcrop scale, many structural geologists turned to this as an explanation for the huge features recognised by Eskola, even suggesting that the “mantles” were above profound unconformities.  Eskola’s view was that these regional features were due to differential uplift of low-density gneisses and more dense supracrustal rocks, and this view lingers with many other geologists.  Christain Teyssier and Donna Whitney, of the University of Minnesota, have reviewed the current state of knowledge for the phenomenon (Teyssier, C. & Whitney, D.L. 2002.  Gneiss domes and orogeny.  Geology, v. 30, p. 1139-1142), and conclude something more involved than either hypothesis.  Many of the gneiss domes show evidence for the involvement of crustal melting in response to decompression as orogens evolve, almost certainly resulting from removal of the upper crust, either by rapid erosion or extensional tectonics.  As well as forming bodies of melt or near-molten migmatites, such a process weakens he crust, allowing masses of low-density crust, including the partially melted bodies, to rise rapidly.  This feeds further decompression, the whole process becoming an effective means of advective heat transfer in large orogens.

Some old habits die hard

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Earth Pages News does not usually contain book reviews, but two that I read over the Christmas break deserve a comment.  The first, The Lunar Men: The Friends Who Made The Future (Jenny Uglow, Faber & Faber, 2002) shows how what is now becoming known as the geosciences was central to the wide-ranging discourses and research of that group of men who created the foundations of modern science in Britain.  The Lunar Society was a loose association of free-thinking individuals, which included Matthew Boulton, Erasmus Darwin, James Watt, James Priestley, Josiah Wedgwood and James Hutton, who became close friends and collaborators at the dawn of the Industrial Revolution.  All emerged from the religious nonconformism that lay outside the aristocratic establishment of the late 18th century, but each came from different backgrounds.  What united them was an all-consuming curiosity as well as a desire to make a living.  Each was driven in his own way to serve those less fortunate, as well as to take their own wealth and talents to whatever limits they had.  Not one was a specialist, and they shared all their interests, ideas and discoveries, as well as supporting one another intellectually, economically and socially.  These were not men in thrall to peer-review or the building of academic empires.  Collectively they challenged established views of all kinds, and took the greatest delight in doing so, even when subject to physical attack, as was Priestley.

The characters depicted in The Dinosaur Hunters (Deborah Cadbury, Fourth Estate, 2001) are from one or two generations later, and do not cut such a merry dash.  Central figures are Gideon Mantell, William Buckland and Richard Owen.  They worked in a period when the challenge of the Lunar Society had created a state defence of religious orthodoxy (almost a panic), and in which a new and partitioned scientific establishment had emerged.  The first dinosaur remains were discovered by the daughter of a carpenter, subsisting on Poor Relief, who supplemented her family’s subsistence by selling Jurassic fossils that she had become adept at finding on the beaches of Lyme Regis.  170 years before the advent of the Open University, Mary’s brilliant insights brought no academic benefits to her, but many to the Reverend geologists who plagiarised her in exchange for just enough cash to keep her and her family in bread and potatoes.  The central characters, however, are Gideon Mantell and Richard Owen.  Mantell, a rural doctor, became obsessed with ancient reptiles following his and his wife’s discoveries of fragments of the Iguanodon.  He felt driven to make his name in scientific circles from outside the establishment, and a tough time he had, despite his growing insight and assiduous collection.  Owen, who hardly collected a specimen in his entire career, relied on his anatomical skills to describe, classify and steal those of others, such as Mantell.  The founder of the Natural History Museum (with Prince Albert’s patronage), Owen clawed his way to the pinnacle of British science over the backs of those more honest and naïve than himself.  Although he was exposed as a plagiarist and scoundrel by Thomas Huxley, Charles Darwin’s “bulldog”, following the publication of On The Origin of Species, Owen’s main victim Mantell had already died a broken man.  William Buckland, by all accounts a genuinely nice man, ended his days in a lunatic asylum having tried to square the growth of material evidence for evolution with his own deep religious beliefs.

Having read both books in quick succession, it was difficult to avoid the conclusion that the best spirit of the “Lunar Men” seems largely to have departed from our science, while the meanest spirit of Victorian times lingers on among self-promoting empire builders with ever-narrower specialisations.

More pondering on new discoveries

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The recent publications that described extremely old primate remains (Orrorin and Sahelanthropus), which may be early beings on the tortuous road to the emergence of humans, has set the circle of palaeoanthropologists abuzz (see A considered view November 2002 Earth Pages News).  Sooner or later, Scientific American was bound to commission an article in plain words that expressed all the conflicting views and  illustrated them magnificently, and so it has (Wond, K. 2003.  An ancestor to call our own.  Scientific American, January 2003, p. 42-51).