Most climate scientists encourage us to believe that planetary warming caused by gas emission from our energy intensive life style is both new and an inevitable context for our future. Yet, one leading authority on past climates, William Ruddiman of the University of Virginia, reminds us that it isn’t only cars and power stations that release warming gases (Ruddiman, W.F. 2005. How did humans first alter global climate. Scientific American, v. 292 March 2005, p. 34-41). New evidence from air bubbles in the Vostok core through Antarctic ice shows a strange deviation of atmospheric CO2 around 8000 years ago, from a downward trend in the early Holocene to one that relentlessly rises to the levels that characterised the recent pre-industrial world. At around that time early agriculturalists in Europe and China began to chop down forest to make fields, thereby releasing the carbon content of felled trees to the atmosphere as CO2. By 5000 years before present, rice cultivation in East Asia had begun the release of methane from waterlogged paddy fields, and the methane content of ice bubbles reveals a reversal of methane decline at that time exactly.. Ruddiman’s view is that the release of both “greenhouse” gases reversed a natural cooling trend, and that growing populations sustained growth in atmospheric CO2 (methane is quickly oxidised in the atmosphere). Comparing the rising CO2 of the Holocene with its records in ice-bubble for the previous three interglacials, shows that in each previous case the gas rose to a maximum early in the interglacials and then declined steadily. The invention of agriculture and its spread from around 11000 years ago in the Near East, he claims, could have staved off the onset of global cooling and the climatic descent into another glacial epoch, by eventually adding 40 parts per million of CO2 to the air. To support his hypothesis Ruiddiman compares the more recent ice-core records with historic catastrophes, mainly plagues that wiped out substantial proportions of the word population . Sure enough, there are falls in CO2 at the time of each major plague; that between 540 to 542 AD in Europe, the Black Death of the Middle Ages, and the reduction of the population of the Americas by maybe 90% when “Old World” diseases such as smallpox and measles met no resistance among native peoples. In many respects Ruddiman’s ideas seem plausible, until we see the data. The problem with ice core data is that its resolution degrades through time, and before 70000 years ago, no annual layers are preserved in glacial ice. Moreover, records from different Antarctic cores differ wildly for the historic period and Ruddiman does not show the record from Greenland ice. Finally, records of ice volume and ice-cap temperatures, derived from marine and glacial oxygen isotope records, show that each previous interglacial involved very different fluctuations in many other climate-related parameters. If nothing else, Ruddiman’s ideas will be challenged and the issue will “run and run” until the next “big thing”.
Tiny Indonesian hominids get the SciAm treatment
The tiny adult remains of Homo floresiensis reported in 2004 (see The little people of Flores, Indonesia, November 2004 issue of EPN) astonished the palaeoanthropological community more than any discovery since René Dubois’ found the first H. erectus remains on nearby Java almost a century ago. Their recent geological age (about 13 ka), together with evidence for cohabiting the island of Flores with fully modern humans and legends of the ebu gogo – “the grandmother who eats anything” spice up the find no end. So it is not surprising that Scientific American has commissioned an excellent popularised account of where things stand with the little people only a few months after the discovery was announced in Nature (Wong, K. 2005. The littlest human. Scientific American February 2005 issue, p. 40-49). It is not just the sheer tinyness of Homo floresiensis that draws our attention, but the fact that with a brain no larger than 2 Ma old australopithecines, the species crafted tools that are far more sophisticated than those of their most likely ancestor, H. erectus. They also found their way across a seaway that could never have dried out during glacial maxima, used fire, and just as important survived competition with fully modern humans for around 20 ka. Yet, as the article is at pains to point out, the find is so new that it is easy for specialists to kid themselves into believing a great deal more than may eventually turn out to be likely. With two cultures on one small island, there may well have been mixing of artefacts, and also occupation of the site – a large cave – by both over the long period when they shared the island. Opinion of many leading figures in the field is related by Kate Wong, and it is very clear that there is a lot of puzzlement.
The oldest modern humans
For a long time it has been known that the “front line” between fully modern humans and European Neanderthals was in the Middle East, with fluctuating occupation of highly productive sites since around 100 ka. It is also well established that the ancestors of all of us outside Africa began to migrate some 70 to 80 thousand years ago, the signs being that the pressure was drying of the continent as global climate cooled. The route take is not at all well defined, but one possibility is across the Straits of Bab el Mandab at the entrance to the Red Sea as islands became exposed when sea level began to fall. So, fully modern humans originated in Africa, but where and when? Unsurprisingly because of the intensity of research there since the discovery of Lucy, the Afar Depression of Ethiopia has provided most remains of H. sapiens sapiens. Volcanic ash layers in sediments that contain specimens there give ages up to about 160 ka. But Ethiopia has other hominid-rich sequences, including ones that have yielded anatomically modern humans. The most notable is the Late Pleistocene Kibish Formation of the Omo River basin in southern Ethiopia, a deltaic sequence that formed when Lake Turkana had higher levels. Human remains occur in the lower part of the Kibish Formation, and as luck would have it, they occur between two volcanic ash horizons and can be accurately dated (McDougall, I et al. 2005. Stratigraphic placement and age of modern humans from Kibish, Ethiopia. Nature, v. 433, p. 733-736). For the moment, they are the oldest proper humans at 195 ka. That age has interesting connotations as regards the climatic conditions of their lives. The Omo basin shares watersheds with drainages into the Blue and White Nile system. At 195 ka increased deposition of organic matter characterised the sediments beneath the Nile delta, which suggests greatly increased rainfall in the uppermost reaches of the Nile system. That coincides with the onset of deposition of the Kibish Formation when Lake Turkana stood much higher than at present. The area would have been lush.
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Prize for solving the world arsenic crisis
Almost every month there are announcements of yet more areas of the world that face hazards from natural contamination of groundwater by release of arsenic from whichever minerals host it in sediments. In Bangladesh alone, the WHO estimates that tens of million people are at risk. Although large tracts of the US and other rich countries do have arsenic levels in groundwater that are above the maximum recommended for safety, the crisis is one that most severely affects some of the world’s poorest and most populous countries. To help solve this massive public health problem, the National Academy of Engineering is offering the Grainger Challenge Prize for Sustainability, a sum of US$1 million, to the individual or individuals who design and create a workable and cheap water treatment system that anyone can use for arsenic-contaminated groundwater in Bangladesh, India, Nepal, and other developing countries. The most likely cheap remedy lies in the use of iron hydroxide as a means of absorbing dissolved arsenic, but several other candidates, including coal fly ash and limestone, together with biological precipitation, have recently begun tests.
Incidentally, the action in the UK against the Natural Environmental Research Council, for negligence in failing to analyse for arsenic in Bangladesh groundwater in the early 1990s, on behalf of 400 Bangladeshis affected by arsenic poisoning, recieved the legal go ahead to appeal against an earlier decision by a British court to throw out their case. My thanks to John McArthur of University College London for this news.
Drilling into the San Andreas Fault?
It seems that in order to really get a feel for the physical and chemical processes involved in faulting, drilling into an active one is a good idea, or at least that seems to be the driving motive behind the SAFOD (San Andreas Fault Observatory at Depth) project of the US Geological Survey (Cohen, P. 2005. Journey to the centre of a quake. New Scientist, 5th February 2005 issue, p. 42-45). It might make sense, because pressures of pore fluids near active faults seem likely to exert some influence over whether a fault segment moves or not. Overpressured fluids can serve to lubricate the otherwise sticky fault surface. In the case of the San Andreas, activity is fragmented. Detailed monitoring of microseismicity near Parkfield, California revealed that a mere 100 x 100 metre patch on the fault plane was responsible for much of the activity. It lies about 3 km down, just within reach of oil-drilling technology. In fact the Parkfield segment is one of the shallowest active zones on the whole fault.. There are already holes in place, drilled to 2 km to host monitoring instruments, and new drilling methods eventually will allow sideways puncturing of the fault plane so as to install more. But even sophisticated drilling is still largely a blind operation, which inevitably hits snags, and there have been several in the SAFOD project. One severed communications with existing instruments. The general idea behind SAFOD is that fault displacements propagate from small “nucleation” sites. The length of the fault that undergoes displacement during one movement is generally correlated with the magnitude of the resulting earthquake. Parkfield seems to be such a nucleation site, but since the earthquakes associated with it are of small magnitude chances are that interfering with it will not accidentally release a large one. The benefits, set against the risks and undoubtedly high costs, are mainly that even the tiniest motions can be monitored. Surface monitoring of course cannot investigate pore fluids and other phenomena, and nor can it detect events less than magnitude 0.5, whose energy is absorbed by rock before it can reach the surface. By monitoring what happens in events with a range of small magnitudes, it ought to be possible to develop earthquake theory to the point where at least the role of fluid pressures, the feedback between earth vibrations set off by one event and movements on a later one, and the effects of mineralogy on friction that resists movement can be assessed. Whatever, once in place, the wait for useful results to accumulate could be a long one, so SAFOD is planned for a 15 year lifetime
More information on SAFOD is available at http://www.earthscope.org/safod/index.shtml
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Age range of early fossil treasure trove
The Doushantuo Formation of southern China dates from just before the Cambrian Explosion, and has become a source of astonishing information about animals that preceded the appearance of those with hard parts. It contains fossil embryos, algae, achritarchs, and small bilaterians that are purportedly the Earth’s earliest animals. Moreover the formation rests on the cap carbonates of a diamictite reckoned to represent a late Neoproterozoic glacial epoch, and provides a variable trend of carbon-isotope variation that extends up to the base of the Cambrian in southern China. Because the sequence contains a number of volcanic ash beds it is potentially dateable. Using a single-zircon U-Pb method, Daniel Condon of MIT and colleagues from the Chinese Academy of Science have established the ages of both top and base of the Doushantuo Formation with considerable precision (Condon, D. et al. 2005. U-Pb Ages from the Neoproterozoic Doushantuo Formation, China. Science Express, 24 February 2005). Sedimentation is bracketed between 635 and 550 Ma, the oldest age coinciding with that for the Ghaub tillite in Namibia. Time-calibration of the carbon-isotope record allows it to be matched with others in Namibia, Oman and Newoundland. There is one snag; within the sequence is a formation boundary that signifies non-deposition, which the authors correlate with a glacial epoch recognised in Newfoundland (the Gaskiers diamictite), citing sea-level withdrawal as the cause of non-deposition in China. The well-constrained correlation suggests a major, global increase in the burial of 12C that produced a marked negative excursion in d13C that spans around 90% of the Ediacaran Period that saw the rise of large soft-bodied animals shortly before the emergence of shelly faunas. The interpretation placed by the authors on this signature of burial of dead organic matter, which relates to no sign of glaciation, is that it would have elevated oxygen levels in the Late Neoproterozoic oceans. That might have increased productivity by primitive eukaryotes, and possibly opportunities for predation. The uppermost part of the Doushantuo Formation broadly coincides with the first appearance of complex trace fossils and mollusk-like bilaterians, and elsewhere there are signs of the first reef formation by weakly calcified metazoans at around that time. Clearly, it is well-dated sections such as these that may hold the key to what exactly prompted the general secretion of skeletal material; the hallmark of the 10 Ma later explosion in fossil animals.
No graphite in Akilia apatites, no sign of life?
In the first EPN of 2005 evidence was reported that weighed against a sedimentary origin for the ~3.8 Ga ironstones of West Greenland from which isotopically light carbon had been claimed to indicate the earliest signs of life (see Iron isotopes enter the Archaean life debate January 2005 EPN). The original work that claimed a biological signature in carbon from the oldest known metasedimentary rocks focussed on carbon-isotope analyses of apatites in them, in the belief that they would have withstood intense metamorphic alteration because of the resistance of that mineral to chemical reactions. Following close on the heels of that revelation comes one a great deal more worrying for aficionados of biogeochemistry. Geoscientists from Estonia, France, the US and Sweden have systematically made petrographic observations on apatite grains from the rocks of the Akilia Association, including those originally reported as carrying geochemical signs of life existing at that time (Lepland, A. et al. 2005. Questioning the evidence for Earth’s earliest life – Akilia revisited. Geology, v. 33, p. 77-79). Of the 190 individual apatite grains examined in 17 rocks, not one showed the slightest trace of carbonaceous material. It seems that apatite is unlikely to have been the host for the low d13C that caused such a stir in palaeobiological circles when it was first announced, and may well not be a good place to look for biomarkers. It also throws into question what did produce the signal. If it was the bulk rock, then the depletion in 13C could have resulted from temperature induced isotopic fractionation. Another possibility is that the samples were contaminated with modern biological materials, despite the precautions taken to avoid that.
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Warming may have triggered Northern Hemisphere glaciation
While I write this issue of EPN it is supposed to be early spring outside, and that is clearly what the ducks reckon as well – they are beginning to, er um, frolic. But there has been two weeks of snow and frost. Britain and the rest of Europe owe the frigid snap to cold air spilling westwards from northern Asia; the influence of the Siberian winter high-pressure area. Although somewhat lost in the recent kerfuffles about whether or not global warming is a fact or a misreading of data, the inevitable build up of mid-continental cold dense air in winter might have interesting consequences, should climate warm. Normally, areas far from the oceans remain dry as well as getting very cold through radiative heat loss in winter. When spring comes, such snow as there is soon disappears and the extremes of cold are replaced by surprisingly high summer temperatures, as anyone who has visited Siberia or Northern Canada will know. Should moist air find its way into such areas during winter, vastly more snow would fall. Its melting would take longer, and more solar radiation would be reflected back to space in spring. Such an albedo feedback could induce generalised cooling. Now evidence has emerged that the earliest known growth of land ice in North America was linked to warming of the ocean from which winds blew over it (Haug G.H. et al. 2005. North Pacific seasonality and the glaciation of North America 2.7 million years ago. Nature, v. 433, p. 821-825). In fact it is axiomatic that growth of continental ice sheets requires a supply of moisture and snow that exceeds the rate of summer melting and ablation, as well as cold winters.
Most theorising about the onset of Northern Hemisphere glaciation has centred on changes in North Atlantic circulation due to closures of the straits where the Isthmus of Panama now links North and South America, and the start of southward deep-water circulation from the latitude of Iceland. In fact both are known to have preceded the last Ice Age by a good 2 Ma. The actual start around 2.7 Ma coincided with an increase in obliquity of the Earth’s orbit that would have led to periods with cold northern summers. Without abundant mid-continent snowfall, that in itself would not have set ice sheets forming in earnest. The multinational team of oceanographers studied sea-floor sediment cores from the sub-Arctic Pacific. To their surprise, sea-surface temperatures provided by evidence from planktonic organisms show evidence at 2.7 Ma for on the one hand cooling of the sea surface (from foraminifer oxygen isotopes) yet considerable warming on the other (from organic chemicals secreted by coccolithophores). Resolving this paradox requires a careful assessment of the ecological behaviour of the two groups of organisms. The authors’ explanation involves the onset of density stratification in the North Pacific, so that the surface warmed quickly in summer, retaining warmth during autumn, and warmed slowly in spring from its minimum temperature. Both result from the high thermal inertia of water. The productivity of silica-secreting diatoms plummeted to a fifth of its earlier levels at 2.7 Ma as well, explained by ocean stratification reducing the supply of nutrients from deep water upwellings. Intuitively, a warm sea upwind of the North American continental interior should have generated high snowfall in late autumn and winter. Haug and colleagues modelled the contrasting effects of an ocean with water overturn and mixing with one that tends to become stratified, to simulate snowfall over the North American Arctic. From a situation in the Pliocene with snowfall over Greenland and the Arctic islands, the scenario shifts to heavy snow over the whole Arctic in the earliest Pleistocene. It seems that the trigger for the Great Ice Age was a hemisphere away from the “usual culprit”, the North Atlantic, although its vagaries, once glacial cycles were underway, probably controlled the details thereafter.
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Cyber-tourism
There are so many places one might wish to visit for their scenery and physical geography, yet only limited resources and, of course, time. The availability of high-resolution satellite images, together with free data that show variations in topographic elevation newly released from the Shuttle Radar Topography Mission, enables realistic simulations of just about anywhere. William Bowen of the California State University has exploited this opportunity to give all-comers a view of most parts of the land surface, as if they were looking obliquely downwards from a high-altitude aircraft – geogdata.csun.edu/world_atlas/index.html
Mineral wealth
Although there are many glossy books about museum quality mineral specimens, as well as being expensive they often only cover a selection of those minerals known to science. One of the beauties of the web is that a site can cram in as many pictures and ancillary data as its server permits, and anyone can browse what is on offer. One such site has been set up by consulting geologist David Barthelmy, which not only illustrates more than 2000 different minerals (half the site’s content of 4300) but allows users to examine their molecular structure interactively – webmineral.com
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After the tsunamis
The main aftermath of Boxing Day is of course the millions of survivors, deeply traumatised, without their homes and possessions, short of food and clean water, and threatened by a host of diseases. Second comes the spontaneous generosity of millions of ordinary, but more fortunate people, who within days deeply embarrassed mean-spirited politicians across the globe. Then there are the aid agencies who responded to the unprecedented magnitude and breadth of the disaster. How successful they will have been remains to be seen in the months ahead. Finally, in the public arena, the media has effectively dropped the topic, and the death toll seems to have been capped at “more than 150 000”. It will have been far, far greater than that, judging by the proportion of those reported missing to those whose death is confirmed, particularly for foreign tourists in the affected areas. There comes a point, when the actual number becomes meaningless because of its size, as in the case of the Holocaust; 6 million Jews, maybe 20 million Russians. There is of course an irresistible case for concentrating on the living and the future. That is within the geoscientific sphere.
That a tsunamis warning system failed to be established for the Indian Ocean when it was mooted can only be condemned in retrospect. It is dreadful to contemplate the fact that Boxing Day did a lot of the work needed for risk assessment. It left kilometres-wide scars along all the affected coastlines, which geoscientists are already looking at to assess the mechanisms that either enhanced the power of the waves or, in a few cases, diminished them. Geophysicists knew beforehand that submarine earthquakes of high magnitude affecting the Indian Ocean will likely occur only along the Sunda arc, so any future tsunamis will revisit the places already devastated this time. There are environmental lessons too. Coastlines stripped of their original mangrove swamps, for developments such as prawn farming, lost any protection. Oddly, many environmentalists are decrying the destruction of habitats and pressuring for rehabilitation. But this was a purely natural disaster, which over millennia will have happened again and again, before being restored to a temporary ecological balance.
So, it seems likely that measures to predict future Indian Ocean tsunamis will be put in place, with Thailand as the most likely centre. Yet, seismologists fear that since the Sunda subduction system has failed once, after more than a century of muted activity, there may soon be further high-magnitude earthquakes. Let us hope not. As well as more rapid assessment of seismic magnitude, a warning system requires sea-floor pressure sensors to detect any major disturbance of ocean water, and careful modelling of how that is distributed by bathymetry. Many fear that warnings that are not followed by actual events will induce the “crying wolf” response, and caution care in making warning. The head of the Thai Meteorological service issued warnings following the announcement by the Pacific Tsunamis Warning Centre that a tsunamis had been unleashed in 1999. Although it hit New Guinea and killed several thousand people there, it had no effect on Thailand, so he was dismissed. He has campaigned for an Indian Ocean warning system since then, and has recently been reinstated. When millions have been directly affected, and memory of the events of 26/12 will last for decades, it seems unlikely that “crying wolf” will result in much public outcry.
Warning system or not, the most pressing needs are for effective and swift communications in hazardous times, and for widespread education about what the hazards are and what to do when they are imminent. Throughout the Pacific basin, even school children know what to do – head for high ground, especially if the sea goes down suddenly. There have been fascinating reports of how the culture of ancient tribal people of the Andamans, probably living there for 20 thousand years or more, saved people. A little girl saw ants swarming away from the sea on the fateful morning, and shouted to everyone to go inland. That response may have been inculcated by previous tsunamis. Communications across the affected region were indeed very poor in this case, largely because geoscientists who understood the risk when the magnitude and location of the earthquake became known did not know whom to contact in the Indian Ocean. The answer is surely whoever issues weather forecasts, for most rural people have radios and listen to weather forecasts every day.
Sources: Nature, 6, 20 and 27 January 2005 (see especially Schiermeier, Q. 2005. On the trail of destruction. Nature, v. 433, p. 350-354. This gives an outstanding, brief discussion of the processes involved in the disaster); New Scientist, 8 and 15 January 2005; Science, 14 January 2005 all contain substantial reports and some editorials.
A list of web links to maps, satellite images and other data relating to the Indian Ocean tsunamis has been assembled by David Stevens of the UN Office for Outer Space Affairs in Vienna. After Friday 4th February, this can be accessed through UNOOSA’s web page at www.oosa.unvienna.org/SAP/stdm.
World Conference on Disaster Reduction: words or action?
From 17 to 21 January 2005, delegates representing 168 states met to discuss measures to mitigate the effects of major disasters that have natural causes in Kobe, Japan. The conference declaration designates 10 years for resolving the issues around predicting, warning of and responding to such events (the Hyogo Framework for Action 2005-2015). A New Scientist editorial (Words will never save us. New Scientist, 29 January 2005, p. 3) expressed caution about the fine words, because the actions needed are, in many fields, not well established. Kobe did indeed concretise the intergovernmental pledge to establish not only an Indian Ocean tsunamis warning network, but one that will eventually cover all maritime countries. It also highlighted the success of the Drought Early Warning service, that has a strong focus on Africa. Yet time and again, the UN, EU and well heeled governments have been alerted to this long-lived kind of disaster, only to fail to respond in a way that truly mitigates the affects. Drought-stricken people are kept barely alive by food aid, only to await the next failure of rains without the infrastructure to assist themselves. New Scientist highlights the common factor in failing to survive natural calamities – poverty. One thing characterised the response to Boxing Day: ordinary people everywhere took decisive action to help, financially and practically, thereby embarrassing and shaming their own governments, the “great and good” multinational institutions, and many an attendee at conference such as Kobe.
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Wanna see an earthquake?
Most of us have grown used to thinking that earthquakes have an epicentre at some fixed point beneath the surface. That is not at all true, as the event that set the Boxing Day 2004 tsunamis in motion as been shown to have been a lengthy rip that propagated from Sumatra NNE to the Nicobar Islands, over a period of about an hour. Even quite small earthquakes are distributed and often migrate along a fault line. Christine arson of the University of Colorado has captured what is effectively a movie of a magnitude 8.3 event off the island of Hokkaido, Japan, which can be viewed at spot.colorado.edu/~kristine/tokachi_rupture.gif. The data that she used comes from a network of a thousand highly sensitive GPS receivers set up throughout Japan. Instead of acceleration, measured by conventional seismometers, GPS records actual position in x, y, z coordinates. That enable the actual motions to be imaged as in the movie.
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Evidence goes against end-Permian impact
In December 2004 EPN commented on what appears to be a serious challenge to claims of geochemical evidence that would support a major impact associated with the largest of all mass extinctions in the Phanerozoic, that at the close of the Permian Period and the Palaeozoic Era, around 251 Ma ago. Newly published analyses from two other well-constrained P-Tr boundary sites found no signs of the elements that would be expected from a major collision with a metal or silicate-rich asteroid (Koeberl, C. et al. 2004. Geochemistry of the end-Permian extinction event in Austria and Italy: No evidence for an extraterrestrial component. Geology, v. 32, p. 1053-1056). Koeberl of the University of Vienna and colleagues from the US and UK focussed on platinum-group elements (PGEs), and osmium and helium isotopes. Both sites are stratigraphically similar and dominated by carbonate sediments, with evidence from one site for deepening water that laid down organic-rich marls. Sure enough, there is a “spike” in iridium at the level of these marls, which had been documented at the Austrian site in 1989, and there is another 50 m higher in the sequence. The new work confirmed both, and also found the marl-related “spike” in Italy. But the reason why iridium has been used to suggest extraterrestrial impacts is because, of all the PGEs, it is the easiest to analyse at very low concentrations. That can give rise to “false positives”, for there are purely terrestrial processes that can concentrate PGEs. An unambiguous arbiter between these processes and impacts lies in the isotopic composition of the metal osmium. Rocks of the Earth’s crust have high rhenium (Re) and low osmium (Os) contents, whereas in meteorites the Re/Os ratio is very much smaller. The unstable isotope 187Re decays to produce a daughter 187Os that adds to the common 188Os isotope. Consequently, terrestrial rocks acquire high 187Os/!88Os rapidly after they crystallise from magmas and that “signature” is imparted to the entire surface environment through weathering and solution. On the other hand, meteorites have low 187Os/!88Os ratios, so the two influences on the geochemical record can be distinguished – if you have good enough analytical facilities. The two iridium spikes fail that test, as regards an impact origin. It seems likely that they originated through precipitation of PGEs from sea water under reducing conditions on the deep sea floor. The helium isotope data carry the same negative message; they are typically terrestrial.
Impact-induced extinctions, particularly ones that wipe out a sizeable proportion of all organisms, are likely to be unremittingly sudden – direct effects being felt within hours over the whole planet, and secondary effects such as “nuclear winter” and acid rainfall over a matter of a few years or decades. Radiometric dating is incapable of resolving such short periods, and at the age of the P-Tr boundary probably not even several hundred millennia. Faunal sequences can give a better indication of abruptness. To most intents the marine record at the time does look as if extinction was very sharp, but it does not indicate anything by way of clear evidence for an impact, such as glass spherules, shocked quart grains and other tell-tale signs. The continental record is pretty sparse, so has not figured much in the debate. However, the Karoo basin of South Africa contains thick continental sediments that span the boundary, and is famous for its primitive reptile fauna, some of which became extinct around the time of the P-Tr event. Incidentally, this die-off created the genetic conditions for the adaptive radiation in the Mesozoic that led not only to the dinosaurs but also the mammals and birds. Charting the timing of the Karoo extinctions has proved difficult, although it appears not to have been sudden in a stratigraphic sense. New age data has emerged from studies of palaeomagnetic field reversals in the sediments, together with variations in carbon isotopes, that allow timing to be better assessed through comparison with magnetic and carbon records from other sections (Ward, P.D. et al. 2005. Abrupt and gradual extinction among Late Permian land vertebrates in the Karoo Basin, South Africa. Science [soon to be published, currently available on Sciencexpress at www.sciencemag.org/sciencexpress/recent.shtml]). The signs are that the proto-reptiles died off over tens to hundreds of thousand years due to some protracted crisis, probably connected with the giant continental flood basalt eruptions that formed the Siberian Traps. Those lavas overlap the timing of the P-Tr boundary, and would certainly have added sufficient CO2 to give substantial global warming and also massive emissions of SO2 that would have created chemically hazardous conditions on a global scale.
New predators on the Mesozoic block
Most people have been led to believe that, although the earliest mammals appeared in the Triassic fossil record, throughout the Mesozoic they were tiny and meekly scurried and skulked while the dinosaurs reigned supreme over land, sea and air. They had to wait for the K-T extinction to develop their full ecological potential. That is now a myth, for Chinese strata (yet again) have revealed much larger mammals than ever thought possible, and some of them ate dinosaurs (Hu, Y. et al. 2005. Large Mesozoic mammals fed on young dinosaurs. Nature, v. 433, p. 149-152). One indisputable mammal skeleton contained the bones of young dinosaurs in its body cavity. In fact so many that one wonders if it met its end through greed.
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Interbreeding: louse study leads to head scratching
A challenging question about the origin of fully modern humans is whether or not Homo sapiens interbred with archaic species, such as the Neanderthals or H. erectus. That modern humans occupied the same territory as both, at the same time, is well established for Europe and Asia. The likely time for the first major migration of moderns from Africa is about 70 to 100 thousand years ago, and archaic humans did not become extinct in Eurasia until 30 ka at the earliest. Genetic material from extinct humans is rare and difficult to analyse because of degradation. A couple of mtDNA samples from Neanderthal remains give results that are sufficiently different from ours to rule out retention in modern human populations of the genetic outcome of any interbreeding between ancestral moderns and the population to which the two Neanderthals belonged. Yet it does not rule out such interactions with other archaic groups. We have no idea of the genetic diversity of Neanderthals, whose lineage probably split from that of our own (through that of H. heidelburgensis) as long ago as 700 ka. If they lived in isolated bands of a small population, that diversity could have become substantial over such a long time. So far, no genetic material has been recovered from H. erectus remains. Another approach to the matter has emerged from a genetic study of human head and body lice – Pediculus humanus (Reed DL. et al. 2004. Genetic analysis of lice supports direct contact between modern and archaic humans. Public Library of Science Biology, v. 2, e340 – through www.plos.org). The louse Pediculus humanus is unique to humans, and genetic comparison with that which infests chimpanzees suggests that these two species diverged at about the same time as the split that led to modern humans and chimps, at about 5.6 Ma. That is remarkably similar to molecular timing that uses primate DNA. The interesting feature of the louse genetic analyses by the team from the Universities of Florida, Utah and Glasgow is that there are differences between the lice that leap on us. There are two strains which originated before 1 Ma ago, according to the molecular clock. One has a global distribution, and infests both head and body, whereas the other is exclusively a head louse and only occurs in the Americas.
Around 1 Ma there seems also to have been a major divergence among early humans between a strand of H. erectus, which survived until as recently as 20 ka in Asia, and one that led to European Neanderthals and the modern humans who began to migrate from Africa to Eurasia around 100 ka. The unique occurrence of the head-only louse in the Americas (along with the other strain) suggests that the modern humans who crossed the Bering Straits to colonise the Americas came into direct physical contact with beings who carried that particular strain, en route. The likely candidates would have been Asian H. erectus. Contact had to be direct, because, unlike the flea, the louse cannot leap, and it can only survive on humans. The lack of the New World Pediculus humanus in Eurasia suggests two things: if moderns were “in touch” with archaics, the latter carried the other variant (Neanderthals?); the present Asian population (and that of New Guinea and Australia) possibly did not have close contact with archaics who were alive at the time of colonisation (were there by then very few?). All very interesting, but it does not resolve the question of interbreeding; intimate contact could have been through fighting, trading or interbreeding. There is another, very different human-only louse, Pthirus pubis, which infests pubic hair only, and about which there is very little genetic information, so far…
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Mars, planet of 2004
As 2004 was but a few days old, there was much cheering at NASA’s Jet Propulsion Laboratory as the two Mars landers touched down safely and unleashed the two Rovers to deploy their instruments. Celebrations at ESA were not so universal, as the Beagle-2 miniature geochemistry laboratory vanished without trace. Beagle could in principle have proved the existence or otherwise of Martian life, had it survived and landed on suitable ground. Still, ESA’s Mars Express orbiter was safe and promised oodles of highly detailed pictures and other data. What followed was an embarrassment of riches from both the US and EU missions, more or less throughout the year. Then ESA had real cause for partying as 2005 opened, as its Huygens probe landed on the largest and most enigmatic moon in the solar system, Saturn’s Titan, but that is a story that will run this year, and it was carried courtesy of NASA’s Cassini mission. New Scientist featured an excellent summary of the achievements on Mars in its 15th January 2005 issue (Chandler, D.L. 2005. Distant shores. New Scientist 15 January 2005, p. 30-39). Everything has worked better than expected, Rovers Spirit and Discovery having the benefit of sand blasts that cleared the dust off their solar cells. They are still functioning, though not exactly prancing – it has taken a year for them to travel just over 5 km between them. But the treasures they have unfolded have delighted lots of geologists. There is ample evidence at least for the former influence of liquid water at the surface, which has both weathered the Martian surface to produce iron minerals that witness both water and highly acid conditions and also laid down sediments in layer after layer. Some hint at the former existence of a large shallow, salty sea where Discovery landed. Mars Express’s imaging devices have produced high-resolution pictures that confirm the influence of water’s sculpting, seemingly late in its history, and the presence of recent glacial deposits. The orbiter also carries a deeply penetrating radar device (MARSIS) capable of finding water up to a kilometre beneath the surface, though it has yet to be deployed. Perhaps the most intriguing find is that Mars’ atmosphere has more methane in it than seems possible, unless something is continually emitting it. That “something” could be volcanism (2004 also revealed signs of previously unknown, recent eruptions), methane may be leaking from sub-surface gas-hydrates similar to those beneath Earth’s sea floor, it could be emitted by icy material from comet debris, and maybe it signifies some primitive, methanogen life forms that are respiring. The last needs to be tied down very rigorously before scientists get over excited. Even if it matches up with signs of emitted water vapour, which it does, that could still be an abiogenic phenomenon. There can be little doubt that Mars is proving irresistible as a political draw, riding on its kudos to hammer out the old message that “Man Must Go There!”. But consider this: had today’s robotic technology and analytical miniaturisation been possible 35 years ago we would know vastly more than we do about the evolution of our neighbour the Moon. Instead of carrying astronauts and their weighty life support systems, the Apollo missions would have brought back an equivalent mass of lunar rock. The same goes for Mars, surely, on the old basis of getting “more bangs for your buck”. But that is a scientific outlook, and maybe the bucks can only be raised by the romantic notion of some brave souls treading where Edgar Rice Burrough’s John Carter once rode astride his banth. But of course, robotic science can also ride on that “vision”, for what could be more catastrophic to whichever US president succeeds in making George W. Bush’s dream come true to find that it is not safe enough out there, and the astronauts do not come back.
Plotting meteorite falls
Museums host collections of thousands of meteorites donated by collectors over more than a century. Although they are the source of much of our understanding about the timing and processes involved in the origin of the solar system and of the Earth itself, the collections are biased towards those that are most easily spotted on the ground. Metallic meteorites show up much more readily than do those made of silicate minerals, which resemble ordinary terrestrial rocks in colour and density. Only when collectors pore over very uniform, light coloured surfaces, such as ice caps, deserts and bare limestone plateaux, can they be assured of a truly representative selection of types. Also, many meteorite samples are weathered and contaminated with earthly materials, because they have lain around on the ground for a long time. Improved precision and detection limits of the chemical analytical tools that meteorite specialists use demand fresh material, as do researchers interested in organic materials carried from space – the embarrassment of having an announcement of a fossil bacterium in a meteorite and then finding that it is some common bug from soil is career threatening. Most important are trying to overcome the compositional bias and to see from which part of the sky different kinds of meteorite come. Phil Bland of Imperial College, London is trying to solve all problems at a stroke. His idea is to set up a network of wide-angle sky cameras to record meteor trails, so that computer analysis of the film will triangulate the point of impact and also work out the precise orbit of the offending body. The ideal place – easy to get to, safe, flat, dry unvegetated and dominated by pale rock – is the infamous Nullarbor (“No Tree”) Plain of SW Australia, which is one of the most featureless places on Earth. Bland already has one sky camera in place that has sensors that only turn it on if the sky is clear, and an internet connection that e-mails him if something as malfunctioned. In one year it spotted 12 trails bright enough to have resulted in meteorites falling to the surface. With three cameras, he hopes that results will be sufficiently accurate to narrow search areas to a square kilometre. If funded, the extended project will even incorporate e-mail alerts to teams of local collectors, whenever a trail exceeds a certain brightness. They should then be able to pristine recover material in a few days.
Source: Muir, H. 2004. Catch a falling star. New Scientist, 25 December 2004, p. 45-47.
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And was there a mighty wind?
Readers will be familiar with the to-ing and fro-ing that surrounds the idea of Neoproterozoic Snowball Earth episodes from earlier issues of EPN. The leading proponent and sturdy defender of the hypothesis, Paul Hoffman of Harvard University, re-enters the fray as co-author of a paper that builds on the idea that following global glaciation the climate became not only very warm but also violent (Allen, P.A. & Hoffman, P.F. 2005. Extreme winds and waves in the aftermath of a Neoproterozoic glaciation. Nature, v. 433, p. 123-127). They document evidence from “cap carbonates” in northern Canada and Spitzbergen that succeed diamictites of “Marinoan” (~635 Ma) age, in the form of large-scale sedimentary structures. Many of these are submarine ripples with amplitudes up to 40 cm, and forms that suggest they were produced by sea-bed motion due to surface waves, down to 200-400 m, far deeper than modern storm-wave base. Central to their argument is hydrodynamic modelling of wind speeds that might have produced such large ripples, and their specific shapes – steep sided. Being based on experiment and observation of modern sea-bed processes, the theory seems quite rigorous. It retrodicts wave periods that are somewhat longer than those commonly seen in modern ocean storms. From that they derive sustained wind speeds that exceed 70 km per hour across open oceans, extraordinary by modern ocean wind standards.
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Another year passed
Because of the horrific events at the end of 2004, this is not a time to celebrate geoscientific achievements during the year that has passed.
The horror of Boxing Day
Unlike the collapse of Manhattan’s Twin Towers on 11 September 2001 the world’s cameras were unable to focus on the minutiae of terrible events around the rim of the northern Indian Ocean. They did not catch the sudden dawning of fear, but the tsunamis of 26 December 2004 were witnessed by millions of coast dwellers in Indonesia, SW Thailand, Sri Lanka, eastern India and as far away as Somalia, Tanzania and Kenya. At the time of writing the death toll had reached 150 thousand, but it will rise inexorably, and countless people’s lives will be blighted for years to come. The world did change on Boxing Day 2004 in a way that dwarfs the events of “9/11”. The majority of those swept in minutes into a debris-loaded sea were among the poorest of their communities, and the dead are dominated by children and old people who simply did not have the strength to save themselves. News came first from popular tourist resorts dotted on palm-fringed beaches, through cell phones and from hastily shot videos of what must at first have seemed a curiosity. Before great waves appeared, the sea drew back to leave fish flapping on beaches, which local children rushed to gather as an unexpected benefice. Ocean waves driven by great seismic events have immense wavelengths, so previously unseen sea floor lingered for 10 to 20 minutes before devastating surges suddenly rose above the horizon..
Off the western coast of Sumatra, a subduction-zone thrust displaced the sea floor by several metres, into which an unimaginable tonnage of ocean rushed. Its rebound set in motion the most devastating natural phenomena, yet on the open ocean their passage would have been imperceptible because of their broad wavelength. Unlike wind-waves, tsunamis travel extremely fast, around 400 km per hour; they are seismic disturbances affecting the entire water body. The further they travel the greater the volume they affect, so they dissipate with distance. Two days after the initial shock, sea-level rose perceptibly in California, half a world away. When tsunamis meet shallows, the frictional effect causes the wave to slow, rise and steepen. The wave breaks far offshore in shallow water, resulting in a surge that rises inexorably on land. It rips up sea-floor materials, including boulders where they are present. Damage and deaths result mainly from the backwash that can rip debris and victims several kilometres out to sea, until the next tsunami arrives, and in this case there were at least three. We have all seen the aftermath, like nuclear devastation but not sterile. Debris, rotting flesh and sewage breed disease, and as many may die from cholera, insect-borne disease and exposure as perished on Boxing Day morning.
The magnitude of the Sumatran sea-quake was 9.0 on the Richter Scale. That is a logarithmic measure of the ground displacement, so that for every increase of 1.0 in magnitude ground motion increases by 10 times. However, it is the energy released that damages and the corresponding increase is 32 times. The Sumatran sea-quake was the largest recorded since that off Alaska in 1964 (magnitude 9.2) and the fourth largest in a century. Tsunamis generated off Alaska reached a height of over 60 metres close to the epicentre, but they travelled parallel to the coast of the Americas and caused only 130 deaths. Those of 26 December 2004 hit land head on, and there are large, densely populated coastal tracts around the Indian Ocean that are below 10 m above mean sea level. Buildings, particularly for poor people, are fragile and lightweight, so the devastation was almost total, unlike the effects of on-land earthquakes. In their case, single-storey dwellings that are little more than wood and grass structures cause less deaths than in areas with multi-storey dwellings made of stone or concrete, and the effects are localised.
The US National Oceanographic and Atmospheric Administration (NOAA) is responsible for tsunamis warnings for the eastern Pacific (http://wcatwc.gov/), which are issued in the same way as extreme weather warnings. Other organisations maintain a permanent watch and warning service for the entire Pacific basin, which is surrounded by the majority of the world’s large earthquake zones, mainly connected to subduction, and is the most prone to tsunamis. Using bathymetry and landmasses, it is possible to model in detail the wavefronts of tsunamis and their travel times for any circum-Pacific earthquake. So adequate warning is possible for most coastal areas following a major earthquake. The Indian Ocean has only one major, tectonically dangerous plate margin, where the Indian Plate drives beneath Eurasia to form the Sunda Trench off the Indonesian archipelago. Although discussed as recently as mid-2004, no tsunami-warning service is in place for the Indian Ocean. One reason given for this lack of foresight is that the north-western part of the Sunda Arc has had little major seismicity for more than 150 years. Therein lay the danger; subduction was locked and a major earthquake grew more likely the longer the quiescence lasted. All the world’s seismic observatories recorded the massive disturbance and the exact location of the Sumatran event within minutes of its occurrence, but no warnings were issued. The tsunamis arrived in Sri Lanka and India over 4 hours later, though within less than half an hour in Thailand and Sumatra, which were most devastated. For the millions whose lives have ended or are in ruins, the greatest advance in the geosciences, plate tectonics, utterly failed them.
What is to be done?
Many geoscientists take pride (and a fair amount of public funding) in focusing their research on dangerous natural phenomena, supposedly aimed at giving warnings or mitigating their effects. Take any natural calamity, whether it be earthquake or tsunami, volcanic eruption, mudslide, flood or even something so simple as helping provide clean water for the victims of drought or displacement by conflict. Now list the lives saved by the direct efforts of geoscientists against the torrent of their publications and attendances at conferences. Is there any cause for pride in the instrumentation, the theory and the field experience? Or should we reflect on the hubris of scientific endeavour in the aftermath of such awful events? Two days after the disaster struck I put together detailed topographic elevation data (from the Shuttle Radar Topography Mission – SRTM) for the coastlines that surround the Indian Ocean. I had had them for 6 months, but did nothing except make some pretty maps for a conference presentation. I had known what potential they have for predicting areas of flooding, and more important where refuges from inundation might be, but I found “better” things to do. All coastal areas below 15 m elevation are at risk, and a great many correlate with the tsunamis’ worst effects. What we could have done and what we did do generally emerge only in retrospect, and indulging in mea culpa serves no purpose. Individuals have their own agendas, and they are rarely useful in any wider sphere. The organisations that draw scientists together are not in themselves altruistic, but serve largely academic ends. However, human tragedies surely remind us of a wider set of responsibilities, even if only momentarily.
A collective organisation of both knowledge and real needs, which sets aside career and the “advancement of science”, is probably the only means of putting the geosciences to work for fully human benefit. For 40 years such a collective existed in the small form of the Association of Geoscientists for International Development (AGID), which aimed at knowledge transfer from its members to less fortunate areas. For the latter half of its existence, AGID was subsidised by the Canadian International Development Agency. A handful of members met at the 32nd International Geological Congress in Florence during late August 2004, the agenda being wholly about its survival or winding up following CIDA’s withdrawal of financial support. The vote went for continuation. But, despite helping some young geoscientists of the “Third World” make progress, AGID’s small size and limited aims and funding have proved unable to make it a force that matches real needs or the geosciences’ potential for assisting development. Data and theory now present the opportunity to resolve two great challenges: giving every man, woman and child on the planet access to safe drinking water; and predicting and mitigating all natural hazards. Every senior politician in the developed world pays lip service to both, each UN agency convenes to discuss them on a regular basis, and the International Union of Geological Sciences (IUGS) has proposed the International Year of Planet Earth (2005-2007) with those themes at the top of its agenda. IGC-32, the largest ever gathering of geoscientists was dominated by humanitarian themes and the launch of the IUGS initiative. The International Year of Planet Earth was supposed to have been proposed by the Peoples’ Republic of China at the September 2004 UN General Assembly 59. It does not appear on the UN web site, and the supporting web site www.esfs.org gives no news of its adoption. But there have been many “Years of…” and even several “Decades of…” from which we have yet to see any tangible outcomes, and little of the “awareness” that they are supposed to generate, certainly not in those areas of the world towards which they were directed.
One collective of professionals that has had a powerful impact on emergencies since 1971 is Médicins sans Frontières (www.msf.org), founded and administered independently of the world’s “great and good”. Would a geosciences equivalent be feasible and supported? Yet there are measures that even individuals can take. At a UN Office for Outer Space Affairs meeting on the use of satellite data for mitigating disasters (Munich, 18-21 October 2004) www.zki.caf.dlr.de/events/2004/unoosa_workshop/unoosa_programme_en.html – Margaret Andrews Deller of the UK Open University presented her ideas (see link at the above web site) on a simple and low-cost way to reduce the impact of natural disasters. Briefly, she based her suggestions on indigenous people’s deep knowledge of their surroundings. Recognising that, it should be possible to provide communities with graphic images that highlight potential threats, in forms that are low-cost and easily understood by anyone, such as the use of images that incorporate perspective and show features in near-natural colours. Her most important point is that such information would not be just a warning, but a means of showing people their homeland in a way that they can learn from and value. That would bring together those affected with those who come to their aid, should catastrophe strike, and would empower local people to take charge of their lives instead of being victims.
Easily understood information and advice is vital for potential victims of catastrophes, and a quick search of the internet reveals lots on all manner of hazards and how to avoid them. NOAA’s tsunamis website http://wcatwc.gov/ is an excellent example. Such information needs to be recast into forms that people outside the “information society” can easily understand, and to be distributed – not such a massive task. What drew children to south Asian beaches on Boxing Day, the massive withdrawal of the sea, is the first sign of a tsunami. On Pacific islands everyone knows what threat such a weird occurrence signifies, but nobody on the rim of the Indian Ocean did. But isn’t it also essential for geoscientists to donate some of their publicly and industrially funded time to share their expertise directly with those so much less fortunate than ourselves? Without that, our claim to be resolving humanity’s problems is a transparent sham.
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Another large igneous province implicated in mass extinction
At the end of the Triassic Period, around 200 Ma ago, life underwent a major crisis that so far has not been believably connected to either extraterrestrial or geological causes. Previous studies have shown that the mass extinction was accompanied by an decrease in 13C in sediments that suggests a short-lived global warming of between 2-4 °C at the Tr-J boundary. That CO2 levels rose is suggested by a decrease in the density of pores (stomata) on fossil leaves. It has been suspected for some time that the largest known continental igneous event, which accompanied early rifting of the modern Atlantic Ocean basin may have been responsible, but so far the dating of this Central Atlantic magmatic province (CAMP) has not been tied to the boundary conclusively. A large consortium of Italian, French, US, Moroccan and Swiss has addressed the sedimentary and igneous record around Tr-J times in the High Atlas of Morocco (Marzoli, A and 14 others 2004. Synchrony of the Central Atlantic magmatic province and the Triassic-Jurassic boundary climatic and biotic crisis. Geology, v. 32, p. 973-976). There, one of the few uneroded continental flood basalt sequences of CAMP (most preserved CAMP magmas are in the form of sills and dykes in offshore basins) occurs among Triassic and Jurassic sediments. Their base deforms the underlying sediments, suggesting that eruption was onto unlithified sediments, shortly after their deposition. Fossils from the sediments are of little help in tying down the age of eruption, however, Ar-Ar ages of the lavas are all within error of 200 Ma, and tally with magnetic stratigraphy from the Tr-J boundary elsewhere. Both age and geochemistry of the flows are remarkably similar to those of flood basalts from the other side of the Atlantic. Magmatic duration, like that in other large igneous provinces was of short duration, no more than a couple of million years. So it now seems that three of the “big five” mass extinctions (the others are end-Permian, connected with the Siberian Traps, and the K-T boundary and associated Deccan Traps) have at least a partial cause from CO2 release by massive volcanism.
Iron isotopes enter the Archaean life debate
Some years ago geochemists obtained carbon-isotope data from 3.8 Ga rocks in Greenland that seemed at the time to be persuasive evidence for the emergence of life during or shortly after Earth’s most traumatic period. Up to 3.8 Ga the Moon was bombarded by huge projectiles, and its companion Earth would have received at least 13 times the flux of destruction. The carbon was within sturdy apatite grains from supposed iron-rich metasediments, and may have been preserved from later high-grade metamorphism. Doubt has been cast on that hypothesis, either because of the unlikelihood of any carbon remaining unfractionated by heating, or because some aspects of the rocks’ geochemistry suggested that they we of igneous origin rather than sediments. Readers will have seen in previous years’ EPN that a controversy rages over even tangible signs that suggest cellular material from rocks half a billion years younger. Geochemists from France and the US have taken a different tack with the ancient Greenlandic rocks that ought to at least resolve the igneous versus sedimentary origin of the banded iron-rich rocks (Dauphas, N. et al. 2004. Clues from Fe isotope variations on the origin of Early Archean BIFs from Greenland. Science, v. 306, p. 2077-2080). They found that the heavy iron isotope 57Fe is more enriched in the ironstones than in any igneous rocks, with little chance that the difference was induced by thermal fractionation. They are metasediments. But therein lies a surprise. The heavy-iron signatures are greater than in less aged banded ironstones. One way in which that could have arisen is from biogenic precipitation of soluble reduced Fe-2, perhaps involving anoxygenic photosynthesisers – because of the strong capacity of photosynthesis for setting electrons in motion, all such organic reactions create local oxidising conditions, whether or not oxygen itself is produced.
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Torrid times in the Cretaceous Arctic
Despite its latitude (above the Arctic Circle) the sedimentary depocentre of northern Alaska is becoming famous for its Cretaceous terrestrial flora and fauna. Plant remains indicate luxuriant vegetation cover, and high excitement greeted the discovery of 8 species of dinosaurs (4 herbivores and 4 theropod predators (Fiorillo, A.R. 2004. The dinosaurs of Arctic Alaska. Scientific American, v. 291(6), p. 60-67). How dinosaurs were able to survive the darkness of the Arctic winter is a bit of a mystery, unless the migrated as do modern caribou – Fiorillo cites evidence for small juveniles that would have been unlikely to have migrated far, because compared with adults they were much smaller than young caribou. There would have been sufficient winter biomass for survival during the Cretaceous, but seeing and being active as cold-blooded reptiles pose problems. At least one of the species had unusually large eyes, so one of the conditions for dinosaur’s remaining year-round seems established. New data regarding climatic conditions in the far north have turned up after an most unusual and intrepid programme of drilling through a drifting island of pack ice over the Arctic Ocean’s Alpha Ridge, not far short of the geographic North Pole. An extraordinary feature of the programme is that it took place between 1963-74, the core having only been examined in detail in the last year (Jenkyns, H.C. et al. 2004. High temperatures in the Late Cretaceous Arctic Ocean. Nature, v. 432, p. 888-892). The Late Cretaceous part of the cores is black mud rich in terrestrial vegetation remains and marine diatoms, and totally lacking in evidence for dropstones and other debris from floating ice shelves. Unfortunately, the Arctic sediments lack carbonate-shelled plankton remains, so the now standard method of sea-surface temperature measurement is not possible. However, Jenkyns et al. were able to use a method based on the fatty acids that survive in plankton membranes, results from which match oxygen-isotope palaeo-temperature measurements in Cretaceous cores from lower latitudes. Astonishingly, even at polar latitudes, the Cretaceous Arctic Ocean seems to have been as warm as 15°C. Climate modelling based on lower latitude data and estimates of CO2 concentration in the Late Cretaceous atmosphere falls around 10° short of these levels. The conventional modelling requires 3 to 6 times more “greenhouse” warming than generally accepted, to account for Arctic sea temperatures in which we could swim in moderate comfort. Possibly the modelling is awry. One of the most important features of Late Cretaceous palaeogeography was a major seaway across North America that connected the Arctic with tropical latitudes. It existed because global sea level was far higher than now, probably due to the oceans’ volume having been substantially reduced by huge magmatic outpourings on the floor of the West Pacific basin (the Ontong-Java Plateau), earlier in Cretaceous times, together with higher rates of sea-floor spreading. The seaway would have been shallow, and thereby easily warmed. Had poleward currents been possible in it, their flow would have acted very like the modern Gulf Stream to warm high latitudes. Despite palaeoclimatologists reliance on models of heat circulation, it needs to be remembered that they are based on grossly simplified geographic features. If they get it very wrong indeed for the well-studied Cretaceous, that casts doubts on climate modelling’s predictive powers for the course of current climate evolution.
See also: Poulsen, C.J. 2004. A balmy Arctic. Nature, v. 432, p. 814-815
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An electronic antidote to eclecticism
It is a plain to me as to any reader that EPN is eclectic, and in some cases pretty impressionist; how else to write a monthly weblog about the broad spectrum of geoscientific developments? So it is good to see websites with a much narrower focus, yet that manage to inform entertainingly and provocatively. Such a site is www.mantleplumes.org, organised by Gillian Foulger of Durham University, currently a visiting scientist with the Volcano Hazards Team at USGS, Menlo Park, USA. It covers the whole of “plumeology”; the tectonics, the magmatism, ages and wider features, even ideas about the presence or absence of plume-related features on other planets. It has some powerful contributing essayists, such as Don Anderson and Warren Hamilton, who are not averse to scepticism and critiques, and represent work in progress on a book, Plates, Plumes & Paradigms just submitted to the Geological Society of America – a rare event to see preprints of book chapters. It serves an educational role as well, with well-illustrated and up-to-date reviews of the mechanisms involved in large-igneous provinces., and thumbnails on a continent-by continent basis. Jason Morgan came up with the “hot-spot” idea about 33 years ago and launched a revolutionising force in plate tectonics. It is good to see that there is still a vibrancy about the topic.
Ancient art
The hallmark of modern human’s abilities is the art left behind by our ancestors since about 30-40 thousand years ago. Among the most enigmatic are those by Australian native people, that might date back as far as 50 ka. The first were discovered by Joseph Bradshaw and his brother in the Kimberly Ranges of northern Western Australia in 1891. The Geneva-based Bradshaw Foundation (http://www.bradshawfoundation.com/) is developing a comprehensive archive of rock-art images from across the globe, which will uplift anyone who visits it.
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Bacterial reduction of arsenic contamination
Following the tragic discovery ten years ago that tens of millions of Bangladeshis drink groundwater that is naturally contaminated by arsenic, the lessons learnt there have been applied on a global scale. That has resulted in further cases with similar causes coming to light. Remediation is chemically quite simple, and since the US reduced the maximum permissible arsenic level in public water supplies from 50 to 10 parts per billion in 2001 research into methods of removal have increased rapidly. There are a number of methods that are based on adsorption of arsenic by iron and aluminium hydroxides and are low-cost. But it seems that biological activity in aquifers can be equally effective (Kirk, M.F. et al. 2004. Bacterial sulphate reduction limits natural arsenic contamination in groundwater. Geology, v. 32, p. 953-956). In the anaerobic conditions that favour the dissolution of iron hydroxide, which is often the most important source of arsenic in sediments, the conditions are also suitable for chemotrophic bacteria. Among these are species that obtain metabolic energy from the reduction of sulphate ions to sulphide. Where metal ions are also present, they combine with the sulphur to precipitate sulphide minerals. In turn, sulphides readily accept arsenic from solution, thereby helping decontaminate potentially dangerous groundwater. Arsenic-bearing groundwater is also found to have high methane levels, which suggests that methanogenic bacteria dominate its micro-ecosystem when sulphate ions are at low concentrations. Perhaps it will prove possible to encourage sulphate-reducers to thrive in such waters, by the addition of some sulphate by injection. That would a cheap remedy to what seems to be a growing risk in areas that extract groundwater from aquifers that are full of organic matter that creates the oxygen-free conditions that release arsenic into solution.
Bacteria in groundwater seem to have another benefit. Where landfill contaminates subsurface waters with a cocktail of pollutants, the nutrients encourage bacterial colonisation, often in the form of biofilms in pore spaces. It seems that their metabolism generates electrical currents (Gosline, A. 2004. Bug “batteries” send out pollution alert. New Scientist !8 December 2004, p. 17). These create electrical potentials of several hundred millivolts that are easily detected by passive electrical monitoring. The voltage highs occur at the margins of pollutant plumes in the groundwater, and can therefore be used to monitor spread of contamination and to indicate safe supplies.
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Jared Diamond on the Flores “hobbits”
Jared Diamond is a behavioural scientist who specialises in birds of east Asia and the Pacific, but he has made a major contribution to the popularisation of anthropology through his books The Third Chimpanzee and Guns, Germs and Steel. His vast knowledge of the west Pacific makes him an able commentator on the amazing find of tiny people on the island of Flores (see: The little people of Flores, Indonesia in November 2004 issue of EPN). He writes of the sheer diversity of opportunities for colonisation of the archipelagos that separate New Guinea from mainland Asia by Homo erectus, who populated the Far East for around 1.8 Ma (Diamond, J. 2004. The astonishing micropygmies. Science, v. 306, p. 2047-2048). There has been speculation that Homo floresiensis became so small in response to a limited biological productivity on Flores, but Diamond is not at all sure – the Indonesian island chain has luxuriant flora and fauna compared with the Asian mainland. But islands have limits to any population. Homo floresiensis probably arrived as a tiny group that flourished because of negligible competition. Soon reaching the limits of support by the island ecosystem, full-sized colonisers with a limited gene pool would either die out or quickly generate smaller offspring, larger numbers of which could be sustained and reproduce. Another of Diamond’s insights concerns the matter of similar populations on the many equally attractive islands in the chain. If there were, that would imply easy island hopping, and therefore no reason for miniaturisation through evolution. Modern humans have done just that, on the scale of the entire Pacific basin over the last 45 thousand years with no sign of evolving as dwarfed island populations – they had boats. Homo floresiensis’ ancestors almost certainly did not. They could have swum the short distances between the islands at times of low sea-level, indeed they could have seen one island in the chain from the next. In the case of New Guinea, had they reached the nearest island to it in modern Indonesia, they could never have seen it in the distance. Diamond’s greatest surprise is how the micropygmies survived later fully human colonisation from 50 to 18 thousand years, when large people would have colonised the entire chain with ease, before proceeding to Australasia and Oceania. Perhaps they coexisted through having a complementary food economy, as do modern African and Philippino pygmies, by some form of trade. They may even have been too dangerous to hunt or attack. Intellectually attractive as Homo floresiensis might be to us, steeped in Tolkienesque lore, Diamond cuts out the fantasy – they were so unhuman as to make the possibility of their disappearance through interbreeding highly unlikely. Like chimpanzees, they would not only have been unappealing but possibly too unpredictable and strong for cross-species sex to have crossed the minds of fully human colonisers.
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Mars in Science and Nature
A year on from the landings of US Mars Rovers, Science devotes much of its early December 2004 issue to findings from the more revealing of the two missions, Opportunity (multi-authored 2004. Opportunity runneth over. Science, v. 306, p. 1697-1756). The articles are highly detailed accounts of the main finding from the various instruments aboard Opportunity, including the evidence for the activity of acid waters on the ancient Martian surface. Equally interesting and considerably more graphic are important findings about volcanic and glacial activity in much more recent times, that come from the European Space Agency’s Mars Express Orbiter and the High Resolution Stereo Camera carried by it (Neukum, G and 42 others 2004. Recent and episodic volcanic and glacial activity on Mars revealed by the High Resolution Stereo Camera. Nature, v. 432, p. 971-979). Recently, excitement about evidence for living organisms on Mars rose with the discovery of significant amounts of methane in the Martian atmosphere. Methane is likely to have a short life span (around 300 years) in the atmospheres of rocky planets. There are two possible sources: methane-generating bacteria or release from volcanoes. The High Resolution Stereo Camera shows conclusively that volcanoes were active on Mars until at least 5 Ma, when previously the planet was thought to be magmatically dead. If fumarole activity continues, that could explain the traces of methane.
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Tying down the Devonian-Carboniferous boundary
Getting the stratigraphic column properly calibrated from relative to absolute time is all the rage these days (New benchmarks for geological time in EPN June 2004). On the recent stratigraphic chart published in late 2003 by the International Commission on Stratigraphy, the Devonian-Carboniferous boundary has a “golden spike” global standard section and point (GSSP) dated at 359.2 ± 2.5 Ma. Already, that is disputed because of new radiometric dating from an “auxiliary” global stratotype section (Trapp, E. et al. 2004. Numerical calibration of the Devonian-Carboniferous boundary: Two new U-Pb isotope dilution-thermal ionization mass spectrometry single-zircon ages from Hasselbachtal (Sauerland, Germany). Geology, v. 32, p. 857-860). As well as holding the record for length of any publication title yet covered by EPN, the paper contains some intriguing points. That a carefully determined age for the strata at Hasselbachtal has been possible is thanks to about six, centimetre-thick ash beds in richly fossiliferous sediments just above the faunally determined boundary. Twenty-three single-zircon ages from the two ashes just above the accepted faunal boundary give ages of 360.5 ± 0.8 and 360.2 ± 0.7 Ma. Now, to you and I and many less pernickety geochronologists, that spells out the well-known phrase or saying, “within error”, as indeed is that of the GSSP. And, for a convoluted reason based on plotting an age from another tuff with these ages against the palaeontological data, the age presented for D-C itself is 360.7 ± 0.7 Ma. This may be a better age than that of the GSSP. But, so what? The D-C boundary is not associated with any family-crushing catastrophe like the P-T or K-T boundaries, nor even that within the Late Devonian itself. Are “they” going to move the GSSP from its present location in southern France, ratified in 1990, along with the vast pyramid of precious and intricately carved crystal, which no doubts marks its spot? An altogether more serious threat to the established order is the stealthy attempt to abolish the last remnant of the great stratigraphic divisions inspired by Giovanni Arduino’s work in the 18th century; the Quaternary is besieged! One of my spies, not unconnected with this episode of our own emergence on the planet, attended a stormy meeting at the 32nd International Geological Congress in Florence in August 2004, which seemed likely to expunge the Quaternary from the minds of all future geologists. He gleefully reported that a mighty rearguard action had put off that evil day, at least for a while. Sadly, the writing is already on the great IUGS/ICS stratigraphic wall chart – its is no longer there! The last relic in officialdom is in the latest definitive publication (Gradstein, F.M. et al. 2004. A new geologic time scale with special reference to Precambrian and Neogene. Episodes, v. 27, p. 83-100). On page 86, at the very top of the table conferring status on GSSPs, it is written “This composite epoch [the “Quaternary”] is not a formal unit in the chronostratigraphic hierarchy”. So there you have it; the issue is getting things into proportion.
A record of the Palaeoproterozoic lunar cycle
One of the many natural processes that produce rhythmic sediments is the ebb and flow of the tide, twice a day and with an amplitude that peaks and falls twice each lunar month (today a 28-day cycle) to produce spring (new and full moon) and neap tides (the two half moons). Tidal rythmites consist of thin laminae whose thicknesses vary regularly for many cycles. Their occurrence dates back to 3.2 Ga, and along with other sedimentary structures formed by tidal action, such as “herring-bone” cross stratification formed by reversals in tidal currents, prove the presence of the Moon in orbit around the Earth. Fine rythmites can be analysed to work out the length of the lunar month in the past, and help refine ideas on the evolution of the Earth-Moon system. Rajat Mazumder of Asutosh College, Kolkata, India has analysed the earliest known tidal rythmites from the Palaeoproterozoic of NE India (Mazumder, R. 2004. Implications of lunar orbital periodicity from the Chaibasa tidal rhythmite (India) of late Paleoproterozoic age. Geology, v. 32, p. 841-844). His work shows that between 2.1 to 1.6 Ga the lunar month was 32-days long. Remarkably, the record in these sediments is as detailed as found in modern ones from estuarine silts. As well as rhythms, they record occasional perturbations due to storms. Using the changes in the lunar month during the last 450 Ma erroneously suggests that the system emerged from a period around 1.5 to 2.0 Ga following a major collision – that of course is ruled out by a total lack of evidence of such a catastrophe. The new datum suggests instead a steady decrease in the lunar month, that corresponds with the Moon’s gradually receding from the Earth. Energy apparently lost by tidal action is conserved by an increase in the angular momentum of the Earth-Moon system, and that forces the Moon ever further from us – its orbital velocity increases.
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Update on the “Snowball”
Two recent papers add weight to the “against” view expressed in For and against “Snowball Earth in EPN of October 2004” One gives age of 709±5 Ma for tuff immediately beneath a supposed Sturtian diamictite from the western USA (Fanning, C.M & Link, P.K. 2004. U-Pb SHRIMP ages of Neoproterozoic (Sturtian) glaciogenic Pocatello Formation, southeastern Idaho. Geology, v. 32, p. 881-884), which does not tally with the radiometric age (685 Ma) of similar rocks not far away. The other (Calver, C.R. et al. 2004. U-Pb zircon age constraints on late Neoproterozoic glaciation in Tasmania. Geology, v. 32, p. 893-896), gives a 575±3 Ma age for sills intruding a “Marinoan” diamictite in Tasmana, and 582±4 Ma for a rhyodacite immediately beneath it. This suggests that these antipodean glaciogenic rocks are correlative with those in Newfoundland and Norway, that are supposedly representatives of the Varangerian glacial epoch. Yet the authors are pains to state that the Marinoan and the Varangerian are one and the same. Read these papers if you are still confused!
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The boys on the black stuff
Tectonic activity continually re-paves the oceanic part of the Earth, though not in the manner of the awesome night-time machines seen frequently by owlish drivers as they negotiate the contraflows and cones on highways, large and small. Slab-pull helps ease plates apart, forcing asthenospheric mantle to rise and partially melt as pressure falls off. Or, at least that is widely believed, for active mid-ocean processes can only be observed at second-hand through samples scraped from the exposed ridge surface for analysis. What once lay at the guts of spreading centres emerges only when slabs of ocean lithosphere slide nicely over continental margins because of compressive forces related to plate subduction. Gravity demands that such obduction is a rare and special process, since oceanic lithosphere is denser than that of continents. Indeed, as ocean floor ages and cools it become increasingly likely to founder into the deep mantle. Ophiolites represent oddly buoyant parts of the ocean floor, almost certainly because they were once thermally anomalous or quite young at the time of their emplacement. There is no guarantee that they represent run-of-the-mill oceanic lithosphere. However, structures in them, especially a subsurface layer made of innumerable basaltic dykes and little else, show concretely that magmatism was dominated by continual extension; exactly as expected for a former spreading centre. The most studied ophiolite is that of the Semail Mountains in Oman, which exhibits every definitive layer of lithosphere that point to magmatism in an extensional oceanic environment. The crustal part is not the best guide to the ophiolite’s genesis, because melt chemistry varies so much with pernickety vagaries of melting and fractionation. It is the mantle sequence that reveals what went on (Le Mée, L. et al. 2004. Mantle segmentation along the Oman ophiolite fossil mid-ocean ridge. Nature, v. 432, p. 167-172). Laurent Le Mée and colleagues from the University of Nantes focus on chemistry and mineralogy of the well-preserved ultramafic rocks in the Oman ophiolite’s mantle layers. Their results show how a whole number of petrogenetically important chemical features vary systematically parallel to the original axis of spreading, to define three distinct axial segments. Within each are other regular fluctuations that define segments of lesser magnitude. This along-axis chemical variability can be modelled in terms of large variations in the degree of mantle melting (between 10-30%), with the lowest degree coinciding with the major segment boundaries. Those discontinuities also tally with increased numbers of mantle-cutting dykes (not the crustal sheeted dykes). Major segments probably formed from regional upwellings of asthenosphere, whereas those with shorter wavelengths reflect individual diapirs. Along active spreading centres, segmentation of chemical affinities in basalt lavas seems to link with various magnitudes of transform faulting, and it is this local tectonics that shows up so nicely in the Oman mantle sample.
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Archaeology and fluorine poisoning
In 1783, the Icelandic fissure volcano Laki erupted. One in five Icelanders perished, partly because most of their livestock died in the eruption’s aftermath, but also because of direct effects from the geochemistry of the lava. The effects spread to much of continental Europe, but with less gruesome results. There are many archival reports of the presence of a bluish-grey haze or “dry fog” and an acrid smell to the air – probably high sulphur dioxide levels. There was an increase in mortality in Europe too, with 25 % more deaths over and above the annual norm in France, possibly exacerbated by the fog’s coincidence with a scorching summer. The politician-scientist Benjamin Franklin was the first to make the connection between news of the eruption, atmospheric oddities and spectacular sunsets. The spread of volcanic emissions far and wide at the surface can be put down to the relatively quiet effusion of lava from Laki; explosive eruptions generally jet gases and ash upwards to reach the stratosphere. The principal killing agent was the fluorine-rich nature of the gas and ash from Laki, which induced a rapid onset of bone-diseases in humans and livestock alike. That is something special to Icelandic magmatism, the only significant above-sea level part of a mid-ocean ridge system. However, fluorine compounds commonly occur in some volcanic ashes, and mortality spread beyond the immediate effects of volcanism is a major threat. Currently, archaeologists and pathologists are exhuming burials from the time of Laki’s last known killer eruption to seek statistics on the influence of fluorosis in its human victims (Stone, R. 2004. Iceland’s doomsday scenario? Science, v. 306, p. 1278-1281). The signs are bony nodules and spiky fibres that fluorine ingestion, most disastrously from water, produces. Early results reveal many skeletons with clear malformation. Fluorosis leads to a hugely painful and lingering death. Usually it results from a slow build-up of fluorine from contaminated water in areas that are rarely associated with active volcanism. The clearest sign of its onset is a brownish mottling of children’s teeth, and it is easily remedied by changing the water supply. Delivered massively and suddenly, as it was in late 18th century Iceland, gave little chance to its victims. A recurrence would possible be just as disastrous today.
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Neanderthals vs moderns: how come we won?
One of the great paradoxes in palaeoanthropology is how modern humans in Europe survived the last glacial maximum whereas Neanderthals did not. In fact they became extinct some 10 thousand years before conditions reached their coldest. The paradox lies in the fact that Neanderthals were superbly adapted physiologically and behaviourally to life in cold, harsh conditions, having lived through the previous glacial period since at least 200 ka ago. Modern humans evolved, since first appearing around 160 ka, by adapting to conditions in Africa – an environment far different from that of Europe in every conceivable way – and bands migrated outwards, probably because of growing aridity as global climate cooled. Their future was akin to that of Africans from modern Kenya, should they decide to migrate to Arctic Canada. Quite probably Kenyans would survive, because the Innuit are supremely generous and friendly people. They have to be in order to have survived their chosen environment. It is this paradox that concerns archaeologist Paul Mellars of Cambridge University (Mellars, P. 2004. Neanderthals and the modern human colonization of Europe. Nature, v. 432, p. 461-465). Genetic evidence from recovered Neanderthal DNA shows conclusively that the two occupying groups in Europe did not interbreed to any significant extent, so the paradox can therefore not be resolved by complete hybridisation. To what extent were modern humans better equipped with tools than were Neanderthals? The archaeological record shows that from about 40 to 35 ka there was a burst of cultural advance among moderns, that spanned the Middle East to the Atlantic shores of Spain – the Aurignacian technology. It coincided with an equally explosive spread of aesthetic culture, involving such symbolism as to be widely considered as a mark of sophisticated language and communication, perhaps a sign of an advance in brain structure that Neanderthals did not experience. One of the big surprises in recent archaeology of this crucial period was that modern human remains associated with early Aurignacian artefacts turned out to be burials later than the tools were discarded. To some, this left open the possibility that the technological advance may have been achieved by earlier occupants – the Neanderthals themselves. Indeed there are signs that these original Europeans did make cultural advances around that time, in the form of the Chatelperronian artefacts. Mellars points out that moderns of the time did not bury their dead near habitations, whereas Neanderthals made a habit of it, so the inference of especially smart Neanderthals is probably unfounded. There are two geographic patterns associated with the Aurignacian, one arcing through Central Europe to France, the other along the Mediterranean coast, each showing distinct differences in technology. This is regarded as support for two populations of colonising moderns. The Chatelperronian is now regarded as one of many signs of some kind of cultural transfer between Neanderthals and moderns, and therefore of regular contact. Whatever those contacts involved is unknown, but immaterial as regards the fate of the Neanderthals. They disappeared without a trace, by 30 ka at the latest. Mellars’ review concludes with the view that this extinction was a matter of outcompetition, as conditions were steadily deteriorating towards the last glacial maximum. It could well be that moderns, faced by the perils of a move to harsher conditions that were oscillating rapidly due to Dansgaard-Oeschger events, were forced to adapt or perish. The Neanderthals did not, or they did it too late. Their culture had served them well, and why should they have changed it?
A discovery that will run and run?
Do you know why humans have prominent buttocks (the ape has none worth a sidelong glance)? I thought not; most people do not wish to know. Here is how to find out. Begin to walk, preferably in secluded woodland. Now clutch each “cheek”, one in either hand. Do you notice anything? No, the gluteus muscles do nothing, apart from wobble a bit. Now, if this is possible, begin to lope along the path, still with a buttock in each hand. There, they work! Hominids are not just striding bipedalists, but evolved to run: not so fast as to collapse after a hundred metres, but kilometre after kilometre at a relentless lope. This is the conclusion from anatomical and bio-mechanical study of hominid remains, going back to our oldest undisputed ancestors (Bramble, D.M. & Lieberman, D.E. 2004. Endurance running and the evolution of Homo. Nature, v. 432, p. 345-352). The outcome is that modern humans, and probably every earlier species of Homo, can and did run any other animal to exhaustion. The australopithecines probably could run down a hedgehog, but not prime meat. The study goes further, since there is more to running than leaning forward and putting a leg out to stop us falling on our faces. The arms are involved, and flexure of the waist. Mechanically, a higher waist and shorter arms are more effective aids to running, as of course are proportionately long legs. The technical arguments in this hypothesis are somewhat unfamiliar, except to the sports scientist, but one immediate conclusion is easy. No modern hunter-gatherer really likes to run a marathon each day, even though they could, and would much rather sit and watch the world go by, so long as he or she is fed. Unless the utter pointlessness of prolonged physical activity, other than a means of sustenance, becomes a cultural necessity for other reasons, the next stage in human evolution may well see the buttocks atrophy. Legs will shorten, the waist drop and the arms lengthen, once more, to help us knuckle-walk up to the chip shop. There may only be one way to preserve the buttocks; to encourage wolf packs in city parks.
Something to chew over
Much of the human evolutionary story depends on the most enduring of fossil material – teeth. So, dentists have been drawn increasingly in palaeoanthropology. Since species are defined as whole organisms, the use of such tiny fragments as teeth should be worrying. But they are often the only material, and specialists in dentition have convinced themselves that teeth “work” as phylogenetic indicators. But there are always dental variations between individuals, and therefore a danger of doing something akin to cheating with a jigsaw puzzle; forcing misfits into the cussed blue sky part in order to get on. Recent research on the genetics that underlie the development of mouse teeth (Kangas, A.T. et al. 2004. Nonindependence of mammalian dental characters. Nature, v. 432, p. 211-214) shows that different levels of a protein (ectodysplasin) affect the shape changes during development of dentition.. Ordinary mice have different molars, depending on tiny differences in the growth points of tooth crowns during dental development, and that depends on ectodysplasin levels. Clearly, major differences among fossil teeth ought to point to adaptation (and speciation) to very different diets and ways of biting. But now there is a devil in the detail of the teeth of mammals, although the authors do not extend their observations explicitly to those of hominins. Specialists in human speciation will probably rationalise away the possibility of something going awry with the hominin clade, and perhaps rightly so, if the implications of Kangas and colleagues work diffuse to their arena. However, everyone is aware of the dramatic polymorphism of human mastication, from mouth-filling “tombstones” to a tiny pointiness that worries the experienced observer.
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Grow your own bridge, hill or fortress
From time to time, truly odd ideas emerge, even from such a conservative bunch as geoscientists. They are often based on quite mundane science. If you pour sulphuric acid on limestone, of course it fizzes violently because CO2 is a product of the simple reaction. Less noticeable is that the other product, hydrated calcium sulphate or gypsum, is considerably less dense than the calcite in limestone. The solid residue swells. “What if….?”, thought Dutch geochemist Roelof Schuiling (Ravilious, K 2004. The new stone age. New Scientist, 20 November 2004, p. 38-41). His idea was to put the simple phenomenon to practical use; infiltrate sulphuric acid into porous limestone and the swelling will bulge up the surface. This does happen naturally, where sulphide-sulphate oxidising bacteria generate sulphuric acid, which renders limestone to an easily erodable mess, and in some soils generates gypsum lenses that bulge up the ground into surface blisters. Schuiling reckons that the huge sulphuric acid surplus, created partly by removing sulphur from vehicle fuels, could be used as a kind of geo-engineering tool on a vast scale. For instance, the coralline shallows beneath the shallow Palk Straits that separate India and Sri Lanka, could be induced to bulge up and create an island ridge, and so complete what is known as Adam’s Bridge that nearly links the two countries. Closer to home, the Low Countries might become the “Slightly Higher Countries”. Worryingly, the technology to make the process viable is simple, if a little expensive on the scales envisaged. The worry, of course, is yet more CO2 emission plus the effect on the environment of so much sulphate and a massive fall in pH.
