Arabia : staging post for human migrations?

English: SeaWiFS collected this view of the Ar...

The Arabian Peninsula from the SeaWIFS satellite (credit: Wikipedia)

From time to time between 130 and 75 ka fully modern humans entered the Levant from Africa, which is backed up by actual fossils. But up to about 2010 most palaeoanthropologists believed that they moved no further, because of the growth of surrounding deserts, and probably did not return to the Middle East until around 45 ka. The consensus for the decisive move out of Africa to Eurasia centred on crossings of the Straits of Bab el Mandab at the entrance to the Red Sea, when sea level fell to a level that would have allowed a crossing by rafting over narrow seaways. The most likely time for such n excursion was during a brief cool/dry episode around 67 ka that coincided with an 80 m fall in global sea level: the largest since the previous glacial maximum (see Evidence for early journeys from Africa to Asia).

In 2011 finds reported from the United Arab Emirates of ‘East African-looking’ Middle Palaeolithic tools in sediment layers dated at 125, 95 and 40 ka led some to speculate that there must have been an eastward move from the Levant by anatomically modern humans (see Human migration – latest news). That view stemmed from the fact that the earliest date was during the last interglacial when sea level would have been as high as it is today, and around 95 ka it would have been little different. That report coincided with others about freshwater springs having emanated from uplifted reefs around the edges of the Arabian Peninsula during the last interglacial, and the existence of substantial lakes deep within the subcontinent around that time (see Water sources and early migration from Africa). Substantial funding followed such exciting news and results of new research are just beginning to emerge (Lawler, A. 2014. In search of Green Arabia. Science, v. 345, p. 994-999).

Oasis of Green Mubazzarah near Al Ain

Al Ain, a rare spring-fed oasis in the eastern Rub al Khali near the UAE-Oman border (credit: Wikipedia)

A team led by Michael Petraglia of the University of Oxford has used field surveys and remote sensing to reveal a great many, now-vanished lakes across the Arabian Peninsula, including many in the fearsome Rub al Khali or Empty Quarter. They are linked by an extensive, partly sand-hidden network of palaeochannels, which include several of the major wadis; a system that once drained towards the Persian Gulf. As well as abundant freshwater molluscs and other invertebrates, former lakeshore sediments are littered with huge numbers of stone tools, also with East African affinities (Scerri, E.M.L. et al. 2014. Unexpected technological heterogeneity in northern Arabia indicates complex Late Pleistocene demography at the gateway to Asia. Journal of Human Evolution, In Press http://dx.doi.org/10.1016/j.jhevol.2014.07.002). Using optically stimulated luminescence dating, which shows how long stone objects have been buried, the British team has found tools dating back as long as 211 ka, with a cluster of dates between 90 to 74 ka. Modern humans, Neanderthals and even Denisovans may have made these tools; only associated fossil remains will tell. Yet it is already clear that for lengthy periods – perhaps of a few hundred or thousand years – the hyper-arid interior of Arabia was decidedly habitable. It may have been a thriving outpost of emigrants from Africa, whose abandonment as climate shifted to extreme dryness as the last interglacial gave way to Ice Age conditions, could well have been the source of the great migration that colonised the rest of the habitable world. Petraglia’s team has already courted controversy with their claim for anatomically modern humans’ tools in South Indian volcanic ash beds that date to the Toba eruption around 74 ka: considerably earlier than the more widely accepted post-65 ka dates of human eastward migration.

New Feature: Picture of the month

Having belatedly discovered The Earth Science Picture of the Day website (it has been going since September 2000; as long as Earth Pages!) I thought readers of EPN might like the aesthetic boost that it provides. So, on the last day of the month I intend to insert a link to what I think is the best of those contributed to EPOD over the previous 4 weeks or so.

The Great Unconformity of the Grand Canyon (credit: Stan Celestian

The Great Unconformity of the Grand Canyon (credit: Stan Celestian)

EPOD has a vast archive of contributions and each one has a brief description and links to other visual resources.

Improved dating sheds light on Neanderthals’ demise

As Earth Pages reported in December 2011 a refined method of radiocarbon dating that removes contamination by younger carbon has pushed back the oldest accessible 14C dates. Indeed, materials previously dated using less sophisticated methods are found to be significantly older. This has led archaeologists to rethink several hypotheses , none more so than those concerned with the relationship in Europe between anatomically modern humans (AMH) and Neanderthals, especially the extinction of the latter.

The team of geochronologists at Oxford University who pioneered accelerator mass spectrometry (AMS) of carbon isotopes, together with the many European archaeologists whose research has benefitted from it, have now published results from 40 sites across Europe that have yielded either Neanderthal remains or the tools they are thought to have fashioned (Higham, T. and 47 others. The timing and spatiotemporal patterning of Neanderthal disappearance. Nature, v. 512, p. 306-309) . One such site is Gorham’s Cave in the Rock of Gibraltar where earlier dating suggested that Neanderthals clung on in southern Iberia until about 25 ka. Another hypothesis concerns the so called Châtelperronian tool industry which previous dating at the upper age limit of earlier radiocarbon methodology could not resolve whether or not it preceded AMH colonisation of Europe; i.e. it could either have been a Neanderthal invention or copied from the new entrants. Most important is establishing when AMH first did set foot in previously Neanderthal’s exclusive territory and for how long the two kinds of human cohabited Europe before the elder group met its end.

Deutsch: Rekonstruierter Neandertaler im Neand...

Reconstruction of Neanderthal life from the Neandertahl Museum(credit: Wikipedia)

The new data do not quash the idea of Neanderthals eking out survival almost until the last glacial maximum in the southernmost Iberian Peninsula, since material from Gorham’s Cave could not be dated. However, occupation levels at another site in southern Spain in which Neanderthal fossils occur and that had been dated at 33 ka turned out to be much older (46 ka). So it is now less likely that Neanderthals survived here any longer than they did elsewhere.

Neanderthal remains are generally associated with a tool kit known as the Mousterian that is not as sophisticated as that carried by AMH at the same time. Of the Mousterian sites that yielded AMS ages, the oldest (the Hyaena Cave in Devon, Britain) dates to almost 50 ka. The youngest has a 95% probability of being about 41 ka old. Of course, Neanderthals may have survived until later, but there is no age data to support that conjecture. The earliest known AMH remains in Europe are those associated with the so-called Uluzzian tool industry of the Italian peninsula. In southern Italy Mousterian tools are replaced by Uluzzian between about 44.8 and 44.0 ka, while Mousterian culture was sustained in northern Italy until between 41.7 to 40.5 ka.

Châtelperronian stone tools

Châtelperronian stone tools (credit: Wikipedia)

Mousterian tool from France

Mousterian blade tool from France (credit: Wikipedia)

Châtelperronian tools associated with Neanderthal remains occur in south-western France and the Pyrenees. The new AMS dating shows that the culture arose at about the same time (~45 ka) as the Uluzzian tool industry began in Italy and ended in those areas where it was used at about the same time (~41 ka) as did the more widespread Mousterian culture. So the question of whether Neanderthals copied stone shaping techniques from the earliest Uluzzian-making AMH more than 500 km to the east, or invented the methods themselves remains an open question. But does it matter as regards the cognitive abilities of Neanderthals? Copying methodology is part and parcel of the success and survival of succeeding AMH, but o too is the capacity to invent useful novelties from scratch. So, yes it does matter, for Neanderthals had sustained the Mousterian culture for tens to hundreds of thousand years with little change.

The upshot of these better data on timing is that AMH and Neanderthals co-existed in Europe for between 2.6 to 5.4 ka; as long as the time back from now to the Neolithic and early Bronze Age. Even allowing for low population density to make contacts only occasional, this is surely too long for systematic slaughter of Neanderthals by AMH. Yet it gives plenty of time for two-way transmission of cultural and symbolic activities, and even for genetic exchanges: assimilation as well as out-competition.

Incidentally, Scientific American’s September 2014 issue is partly devoted to broader issues of human evolution (Wong, K. (editor) The Human Saga. Scientific American, v. 311(No 3), p. 20-75) with a focus on new developments. These cover: a revised time line; the emerging complexity of hominin evolution  by veteran palaeoanthropologist Bernard Wood.; the influence of climate change; by Peter de Menocal; cultural evolution in the broad hominin context by Ian Tattersall; a discussion of hominin mating arrangements by Blake Edgar; two contributions on cooperation versus competition among hominins by Frans de Wall and GGry Stix; two articles on recent biological and future cultural  evolution by John Hawks and Sherry Turkle (interview).

Did Out of Africa begin earlier?

It is widely thought that anatomically modern humans (AMH) began to diffuse out of Africa during the climatic cooling that followed the last interglacial episode. Periods of build-up of ice sheets, or stadials, also saw falls in sea level, which would have left shallow seas dry and easily crossed. The weight of evidence seems to point towards the narrowing of the Red Sea at the Straits of Bab el Mandab between modern Eritrea and the Yemen. Because the Red Sea spreading axis goes onshore through the Afar region of Ethiopia further north, the Straits today are shallow. Between about 70 and 60 ka, during a major stadial, much of the Bab el Mandab would have been dry. Dating of the earliest AMH remains in Asia and Australasia seems to suggest that the move out of Africa probably began around that time. But, of course, that presupposes the AMH fossils being the oldest in existence, although some would claim that genetic evidence also supports a 70-60 ka migration. Yet, AMH human remains dated at around 100 ka have been found in the Middle East on a route that would also lead out of Africa, but for the major problem of crossing deserts of modern Syria and Iraq. The supposed desert barrier has led many to suggest that the earlier venture into the Levant met a dead end. Should AMH fossils older than 70 ka turn up in Eurasia or Australasia then a single migration becomes open to doubt.

Mitochondrial DNA-based chart of large human m...

Chart of large human migrations based on variations in mitochondrial DNA in living humans(Numbers are millennia before present.) (credit: Wikipedia)

It appears that challenge to what has become palaeoanthropological orthodoxy has emerged (Bae, C.J. et al. 2014. Modern human teeth from Late Pleistocene Luna Cave (Guangxi, China). Quaternary International, In Press). Scientists from the US, China and Australia found two molar teeth within calcite flowstone in Lunadong (‘dong’ means ‘cave’). That speleothem is amenable to uranium-series dating, and has yielded ages between 70 and 127 ka. That antiquity does open up the possibility of earlier migration, perhaps during the interglacial that ended at about 115 ka when sea levels would have stood about as high as it does nowadays (in fact it was only after about 80 ka that it stood low enough to make a move across the Bab el Mandab plausible). If that were the case, the migration route would have more likely been through the Middle East, perhaps along the Jordan valley and thence to the east. Had there been greater rainfall over what is now desert then there would have been no insurmountable barrier to colonisation of Asia.

These teeth are not the only evidence for earlier entry of AMH into east Asia; a date of 66 ka for a modern human toe bone was recently reported from the Philippines. Yet many experts remain unconvinced by teeth alone, especially from east Asia where earlier humans had evolved since first colonisation as early as 1.8 Ma ago. There are other pre-70 ka east Asian bones with more convincing AMH provenance, however.

There is another approach to the issue of earlier Out of Africa migration; one resting on theoretical modelling of the observed genetic and morphological variation among living Eurasians, especially the decreasing diversity proceeding eastwards (Reyes-Centeno, H. et al. 2014. Genomic and cranial phenotype data support multiple modern human dispersals from Africa and a southern route into Asia. Proceedings of the National Academy of Sciences, v. 111, p. 7248-7253. doi: 10.1073/pnas.1323666111). The authors, from Germany, Italy and France, challenge the single-exit hypothesis based on genetic data, suggesting that those data are also commensurate with several Out of Africa dispersals beginning as early as 130 ka. They favour the Bab el Mandab exit point and migration around Eurasia at that time when sea-level was extremely low during a glacial maximum. They hint at the ancestors of living native Australians and Melanesians being among those first to leave Africa, other Asian and European populations having dispersed from a later wave.

Serious groundwater depletion in western US

The 2300 km long Colorado River whose catchment covers most of Arizona and parts of the states of Colorado, California, Nevada, Utah, New Mexico and Wyoming is one of the world’s most harvested surface water resources. So much so that barely a trickle now ends up in Baja California where the huge river once flowed into the sea. The lower reaches of the river system cross arid lands and it is the water source for several major cities and areas of intensive agriculture, serving as many as 40 million people and 16 thousand km2 of irrigated fields. It has been nicknamed the US Nile because of its economic importance, but Egypt’s Nile has far less pressure put on it, although its exit flow to the Mediterranean is also hugely reduced from its former peak volume. The water crisis affecting the Colorado River and the areas that it serves has peaked during the 14-year drought over its lower reaches. To ease conditions in the former wet lands of Mexico near the river’s outlet 2014 saw deliberate major releases from giant reservoirs higher in the Colorado’s course.

English: New map of the Colorado River watersh...

The Colorado River Basin (credit: Wikipedia)

Surface abstraction is not the only drain on water resources of the Colorado River basin: groundwater pumping from the sediments beneath has grown enormously for both irrigation and urban use. That it is possible to play golf at many courses in the desert and to see monstrous musical fountains in Las Vegas is down largely to groundwater exploitation. There have been concerns about depletion of underground reserves once abstraction outpaced natural recharge by infiltration of rainfall and snow melt, but highlighting the magnitude of the problem required a rather dramatic discovery: so much water has been lost from aquifers that the missing mass has reduced the Earth’s gravitational field over the south-west US (Castle, S.L. et al. 2014. Groundwater depletion during drought threatens future water security of the Colorado River Basin. Geophysical Research Letters, doi: 10.1002/2014GL061055).

Global Gravity Anomaly Animation over land fro...

Global Gravity Anomaly Animation over land from GRACE (credit: Wikipedia)

The evidence comes from the Gravity Recovery and Climate Experiment (GRACE), jointly funded by NASA and Germany’s DLR and launched in March 2002. GRACE uses two satellites that follow the same orbit with a spacing of 220 km between them.  Range finders on each measure their separation distance, and so their ups and downs as gravity varies, with far greater accuracy than any other method.  Measuring the Earth’s entire gravitational field at their orbital height takes about a month. Groundwater depletion beneath the Gangetic Plains of northern India, to the tune of 109 km3, was detected in 2009  and the same approach has been applied to the Colorado Basin for nine years between 2004 and 2013. It shows that during this part of one of the longest droughts in the history of the south-west US 50 km3 have been lost from beneath, as a rate of about 5.5 km3 per year. Though the total is half the loss from beneath northern India, it should be remembered that more than ten times as many people depend on the Ganges Basin. Moreover, there is no monsoon recharge in the south-western states.

Any excuse to return to the Moon

Humans first set foot on the Moon 45 years ago, yet by 42 years ago the last lunar astronaut left: by human standards staffed lunar exploration has been ephemeral. Yet for several reasons – romantic and political – once again getting living beings onto other worlds has become an obsession to some, in much the same manner that increasing numbers of countries seem hell-bent in increasing the redundancy of equipment in orbit; redundant because many of the satellites being launched all do much the same thing, especially in the remote sensing field. It’s all a bit like the choice between buying a Ferrari or hiring a perfectly serviceable vehicle when needed – prestige is high on the list of motivators. A new obsession is extraterrestrial mining and some very rich kids on the block are dabbling in that possibility: James Cameron of Aliens and Avatar fame (both films with space mining in the plot); a bunch of Google top dogs; billionaire entrepreneurs and oligarchs with cash to burn. Resource exploitation has also motivated Indian, Russian and Chinese interest in a return to the Moon, at least at an exploratory level.

NASA's proposed Moon colony concept from early...

NASA’s proposed Moon colony concept from early 2001 (image: NASA)

The main prospective targets have been water, as a source of hydrogen and oxygen through electrolysis to make portable rocket fuel, and helium, especially its rare isotope He-3, for use in fusion reactors. Helium is more abundant on the Moon than it is on Earth: only 300 grams of He-3 per year leaks out of the Earth’s depths. On the Moon there may be as much as 50 parts per billion in its dusty regolith cover where it remains supercooled in areas of permanent shadow. But to get a ton of it would require shifting 150 million tons of regolith. A decade ago geologists suggesting that metals might be mined on the Moon – noble metals and rare-earth elements have been mooted (the latter’s export being embargoed by Earth’s main producer China) – would have been laughing stocks, but now they get air time. Yet none of these materials occur on the Moon in the type of ore deposit found on Earth; if they did the anomalous nature of such enrichments on a body devoid of vegetation would have ensured their detection already. Even if there were lunar ore bodies, anyone with a passing familiarity with resource extraction knows just how much waste has to be shifted to make even a super-rich deposit economic on Earth, and that vast amounts of water are deployed in enriching the ‘paying’ metal to levels fit for smelting. For instance, while the rise in gold price since it was detached from a fixed link with paper money in 1971 has enabled very low concentrations to be mined, the methods involve grinding ore in water and then dissolving the gold in sodium cyanide solution, re-precipitating it on carbon made from coconut husks, redissolving and then precipitating the gold again by mixing the ‘liquor’ with zinc dust. Dry ore processing methods – based on density, magnetic and electrical properties – are hardly used in major mining operations nowadays.

The other, and perhaps most important issue with lunar or asteroid mining is that the undoubtedly high costs of whatever beneficiation process is deemed possible must be offset against income from the product; i.e. determined by market price on the home world which would have to be far higher than now. Such a rise in price would work to make currently uneconomic resources here worth mining, and anyone who believes that mining on the Moon would ever be competitive in that capitalist scenario risks being en route to the chuckle farm. Unless, of course, their motive is an exclusivist hobby par excellence and the bragging rights that accompany it – a bit like big game hunting, but the buzz coming from risking their billions rather than their lives.

But it turns out that a refocus on bringing stuff back from the Moon is not confined to floating stock on the financial markets. There are academic efforts to rationalise the Dan Dare spirit. There aren’t many scientific journals with a level of kudos to match the Philosophical Transactions of the Royal Society, the first journal in the world exclusively devoted to science and probably the longest running since it was established in 1665 at the same time as the Royal Society itself. Recently one of its thematic issues dubbed ‘‘Shock and blast: celebrating the centenary of Bertram Hopkinson’s seminal paper of 1914’  (Hopkinson, B. 1914. A method of measuring the pressure produced in the detonation of high explosives or by the impact of bullets. Philosophical Transactions of the Royal Society A v. 213, p. 437-456) a paper appeared that examines the likelihood of fossils surviving the shocks of a major impact (Burchell, M.J. et al. 2014. Survival of fossils under extreme shocks induced by hypervelocity impacts. Philosophical Transactions of the Royal Society A v. 372, 20130190 Open Access).

The authors, based at the University of Kent, UK, used a high-velocity air gun to fire quite fragile fossils of diatoms frozen in ice into water at speeds up to 5.34 km s-1. They then looked at solids left in the target to see if any recognisable sign of the fossils remained. Even at the highest energies of impact some diatomaceous material did indeed remain. Their conclusion was that meteorites derived by large impacts into planetary bodies, such as those supposedly from Mars or the Moon, could reasonably be expected to carry remnants of fossils from the bodies, had the impact been into sedimentary rock and that the bodies had supported living organisms that secreted hard parts. My first thought was that the paper was going to resurrect the aged notion of panspermia and a re-examination of the ALH84001 meteorite found in Antarctica claimed in 1996 to contain a Martian fossil (and believed by then US President Bill Clinton). Likewise it might be cited in support of the similar claim, made by panspermia buff Chandra Wickramasinghe, regarding fossils reputedly in a meteorite that fell in Sri Lanka on 29 December 2012: widely regarded as being mistaken. Yet Wickramasinghe’s team reported diatoms in the meteorite!

The Martian meteorite ALH84001 shows microscop...

The Martian meteorite ALH84001 shows microscopic features once suggested to have been created by life. (credit: Wikipedia)

However, Burchell has suggested that their results open up the possibility of meteorites on the Moon that had been blasted there from Earth might preserve terrestrial fossils. Moreover, such meteorites might preserve fossils from early stages in the evolution of life on Earth, since when both rocks and whatever they once contained have been removed by erosion or obliterated by deformation and metamorphism on our active planet. ‘Another reason we should hurry back to the Moon’ says Kieren Torres Howard of New York’s City University…

Breathing spaces or toxic traps in the Archaean ocean

 

The relationship between Earth’s complement of free oxygen and life seems to have begun in the Archaean, but it presented a series of paradoxes: produced by photosynthetic organisms oxygen would have been toxic to most other Archaean life forms; its presence drew an important micronutrient, dissolved iron-2, from sea water by precipitation of iron-3 oxides; though produced in seawater there is no evidence until about 2.4 Ga for its presence in the air. It has long been thought that the paradoxes may have been resolved by oxygen being produced in isolated patches, or ‘oases’ on the Archaean sea floor, where early blue-green bacteria evolved and thrived.

 

A stratigraphic clue to the former presence of such oxygen factories is itself quite convoluted. The precipitation of calcium carbonates and therefore the presence of limestones in sedimentary sequences are suppressed by dissolved iron-2: the presence of Fe2+ ions would favour the removal of bicarbonate ions from seawater by formation of ferrous carbonate that is less soluble than calcium carbonate. Canadian and US geochemists studied one of the thickest Archaean limestone sequences, dated at around 2.8 Ga, in the wonderfully named Wabigoon Subprovince of the Canadian Shield which is full of stromatolites, bulbous laminated masses probably formed from bacterial biofilms in shallow water (Riding, R. et al. 2014. Identification of an Archean marine oxygen oasis. Precambrian Research, v. 251, p. 232-237).

English: Stromatolites in the Hoyt Limestone (...

Limestone formed from blue-green bacteria biofilms or stromatolites (credit: Wikipedia)

Limestones from the sequence that stable isotope analyses show to remain unaltered all have abnormally low cerium concentrations relative to the other rare-earth elements. Unaltered limestones from stromatolite-free, deep water limestones show no such negative Ce anomaly. Cerium is the only rare-earth element that has a possible 4+ valence state as well one with lower positive charge. So in the presence of oxygen cerium can form an insoluble oxide and thus be removed from solution. So cerium independently shows that the shallow water limestones formed in seawater that contained free oxygen. Nor was it an ephemeral condition, for the anomalies persist through half a kilometer of limestone.

 

The study shows that anomalous oxygenated patches existed on the Archaean sea floor, probably shallow-water basins or shelves isolated by the build up of stromatolite reef barriers. For most prokaryote cells they would have harboured toxic conditions, presenting them with severe chemical stress. Possibly these were the first places where oxygen defence measures evolved, that eventually led to more complex eukaryote cells that not only survive oxygen stress but thrive on its presence. That conjecture is unlikely to be fully proved, since the first undoubted fossils of eukaryote cells, known as acritarchs, occur in rocks that are more than 800 Ma years younger.

 

 

 

Planet Mercury and giant collisions

Full-color image of from first MESSENGER flyby

Mercury’s sun-lit side from first MESSENGER flyby (credit: Wikipedia)

Mercury is quite different from the other three Terrestrial Planets, having a significantly higher density. So it must have a considerably larger metallic core than the others – estimated to make up about 70% of Mercury’s mass – and therefore has a far thinner silicate mantle. The other large body in the Inner Solar System, our Moon, is the opposite, having the greatest proportion of silicate mantle and a small core.

The presently favoured explanation for the Moon’s anomalous mass distribution is that it resulted from a giant collision between the proto-Earth and a Mars-sized planetary body. Moreover, planetary theorists have been postulating around 20 planetary ‘embryos’ in the most of which accreted to form Venus and Earth, the final terrestrial event being the Moon-forming collision, with smaller Mars and Mercury having been derived from the two remaining such bodies. For Mercury to have such an anomalously large metallic core has invited mega-collision as a possible cause, but with such a high energy that much of its original complement of silicate mantle failed to fall back after the event. Two planetary scientists from the Universities of Arizona, USA, and Berne, Switzerland, have modelled various scenarios for such an origin of the Sun’s closest companion (Asphaug, E. & Reuffer, A. 2014. Mercury and other iron-rich planetary bodies as relics of inefficient accretion. Nature Geoscience, published online, doi: 10.1038/NGEO2189).

Their favoured mechanism is what they term ‘hit-and-run’ collisions in the early Inner Solar System. In the case of Mercury, that may have been with a larger target planet that survived intact while proto-Mercury was blasted apart to lose much of it mantle on re-accretion. To survive eventual accretion into a larger planet the left-overs had to have ended up in an orbit that avoided further collisions. Maybe Mars had the same kind of lucky escape but one that left it with a greater proportion of silicates.

One possible scenario is that proto-Mercury was indeed the body that started the clock of the Earth-Moon system through a giant impact. Yet no-one will be satisfied with a simulation and some statistics. Only detailed geochemistry of returned samples can take us any further. The supposed Martian meteorites seem not to be compatible with such a model; at least one would expect there to have been a considerable stir in planetary-science circles if they were. For Mercury, it will be a long wait for a resolution by geochemists, probably yet to be conceived.

Trapping Martian life forms

No matter how optimistic exobiologists might be, the current approaches to discovering whether or not Mars once hosted life or, the longest shot of all, still does are almost literally hit or miss. First the various teams involved try to select a target area using remotely sensed data to see if rocks or regolith have interacted with water; generally from the presence or absence of clay minerals and /or sulfates that hydrous alteration produces on Earth. Since funding is limited the sites with such ingredients are narrowed down to the ‘best’ – in the case of NASA’s Curiosity rover to Gale Crater  where a thick sequence of sediments shows occasional signs of clays and sulfates. But a potential site must also be logistically feasible with the least risk of loss to the lander. Even then, all that can be achieved in existing and planned mission is geochemical analysis of drilled and powdered samples. Curiosity’s ambition is limited to assessing whether the conditions for life were present. Isotopic analysis of any carbon content to check for mass fractionation that may have arisen from living processes is something for a future ESA mission.

Neither approach is likely to prove the existence now or in far-off times of Martian life, though scientists hope to whet the appetite of those holding the purse strings. Only return of rock samples stands any realistic chance of giving substance to the dreams of exobiologists. But what to collect? A random soil grab or drill core is highly unlikely to provide satisfaction one way or the other. Indeed only incontrovertible remains of some kind of cellular material can slake the yearning. Terrestrial materials might provide a guide to (probably) robotic collectors. Kathleen Benison and Francis Karmanocky of West Virginia University have followed this up by examining sulfates from one of the least hospitable places on Earth; the salt flats of the high Andes of Chile (Benison, K.C. & Karmanocky, F.J. 2014. Could microorganisms be preserved in Mars gypsum? Insights from terrestrial examples. Geology, v. 42, p. 615-618).

Evaporite minerals from Andean salars precipitated from extremely acidic and highly saline lake water originating from weathering of surrounding volcanoes. Oddly few researchers have sought cellular life trapped in crystals of salt or gypsum, the two most common minerals in the high-elevation salt pans. Fluid inclusions in sedimentary halite (NaCl) crystals from as far back as the Triassic are known to contain single-celled extremophile prokaryotes and eukaryotes, but gypsum is more likely to be found on Mars. Benison and Karmanocky document a variety of cellular material from Chilean gypsum that has been trapped in the solid mineral itself or in fluid inclusions. This is the most likely means of fossilisation of Martian life forms, if they ever existed. The salar gypsum contain cells that can be cultured and thereby revived since several species can remain dormant for long periods. The authors suggest that transparent cleavage fragments of Martian gypsum could be examined at up to 2000x magnification on future Mars landers. Finding convincing cells would see dancing in exobiology labs, and what if they should move…

Fieldwork and geological education

In March 2013 EPN carried an item connected with the abandonment of field training at week-long summer schools by the UK’s Open University. After 40 years of geoscientific summer schools connected with courses at Levels-1, -2 and -3 anonymous performance statistics were available for thousands of students who had studied those OU Earth Science courses that offered summer-school experiences in the field, first as compulsory modules (1971-2001) then as an optional element (2002-2011) and finally with no such provision. The March 2013 item compared statistics for the three kinds of provision. It should be noted that the OU once had possibly the world’s largest throughput of degree-level geoscience students for a single higher educational institution.

After 2001, pass rates feel abruptly and significantly; in the Science Foundation Course the rate fell from an annual average of 69 to 54%, and in level-2 Geology from 65 to 55%. This was accompanied by a significant decrease in enrolment in equally and more popular geoscience courses that had never had a summer school element. The second statistical drop was of the order of 30 to 40%. It seemed that residential schools played a vital role in boosting confidence and reinforcing home studies, as well as transferring practical field skills. After further falls in enrolment since summer schools were removed from the curriculum in 2012, the OU is in the process of completely revising its geoscientific courses and attempting to substitute virtual, on-line field and lab ‘experiences’. Time will tell if it ever manages to reach its former level of success and acceptance

So, discovering that The Geological Society of America had surveyed attendees at its Annual Meetings (Petcovic, H.L. et al. 2014. Geoscientists’ perceptions of the value of undergraduate field education. GSA Today, v. 24 (July 2014), p. 4-10) piqued my interest. Almost 90% of those polled agreed that field studies should be a fundamental requirement of undergraduate programmes; very few agreed that becoming an expert geoscientist is possible without field experience. Field courses develop the skills and knowledge specific to ‘doing’ geoscience; teach integration of fundamental concepts and broaden general understanding of them; inculcate cooperation, time management and independent thinking that have broader applications. Fieldwork also has personal and emotional impacts: reinforcing positive attitudes to the subject; creating a geoscientific esprit de corps; helping students recognise their personal strengths and limitations. Then there is the aspect of enhanced employability, highlighted by all categories of respondents.

Set against these somewhat predictable sentiments among geoscientists are the increasing strains posed by cost, time commitment, and liability, as well as the fact that some potential students do not relish outdoor pursuits. Yet overall the broad opinion was that degree programmes should involve at least one field methods course as a requirement, with other non-compulsory opportunities for more advanced field training