Author: zooks777

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

The creators of worlds

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

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

Onshore gas hydrate reserves close to recovery

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

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

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

Quantifying motions inside continents

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

Remote sensers now employable

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

Mantle and core do not mix

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

Collapse of the continental margin and methane release

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

Super-eruptions and climate

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

Perspective on the Moon and Mars

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

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

Tectonics and climate, and the rate of mountain erosion

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

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

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

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

Rationalising radiocarbon dating

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

Ancient baby penis worm hits the news

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

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