Earth-logs

Fracking and earthquakes

Published on July 19, 2013 by zooks777Leave a comment

Review of Fracking Issues posted on 31 May 2013 briefly commented on a major academic study of the impact of shale gas exploitation on groundwater. The 12 July 2013 issue of Science follows this up with a similar online, extensive treatment of how underground disposal of fracking fluids might influence seismicity in new gas fields (Ellsworth, W.J. 2013. Injection-induced earthquakes. Science, v. 341, p. 142 and doi: 10.1126/science.1225942) plus a separate paper on the same topic (van der Elst, N.J. et al. 2013. Enhanced remote earthquake triggering at fluid-injection sites in the Midwestern United States. Science, v. 341, p.164-167).

It was alarm caused by two minor earthquakes (<3 local magnitude) that alerted communities on the Fylde peninsula and in the seaside town of Blackpool to worrisome issues connected to Cuadrilla Resources’ drilling of exploratory fracking wells. These events were put down to the actual hydraulic fracturing taking place at depth. Such low-magnitude seismic events pose little hazard but nuisance. The two reports in Science look at longer-term implications associated with regional shale-gas development. All acknowledge that the fluids used for hydraulic fracturing need careful disposal because of their toxic hazards. The common practice in the ‘mature’ shale-gas fields in the US is eventually to dispose of the fluids by injecting them into deep aquifers, which Vidic et al. suggested that ‘due diligence’ in such injection of waste water should ensure limited leakage into shallow domestic groundwater.

The studies, such as that by William Ellsworth, of connection between deep waste-water injection and seismicity are somewhat less reassuring. From 1967 to 2001 the central US experienced a steady rate of earthquakes with magnitudes greater than 3.0, which can be put down to the natural background of seismicity in the stable lithosphere of mid North America. In the last 12 years activity at this energy level increased significantly, notably in areas underlain by targets for shale-gas fracking such as the Marcellus Shale of the north-eastern US. The increase coincides closely with the history of shale-gas development in the US. The largest such event (5.6 local magnitude) destroyed 14 homes in Oklahoma near to such a waste-injection site. Raising the fluid pressure weakens faults in the vicinity thereby triggering them to fail, even if their tectonic activity ceased millions of years ago: many retain large elastic strains dependent on rock strength.

Apart from the mid-continent New Madrid seismic zone associated with a major fault system parallel to the Mississippi, much of the central US is geologically simple with vast areas of flat-bedded sediments with few large faults. The same cannot be said for British geology which is riven with major faults formed during the Caledonian and Variscan orogenies, some of which in southern Britain were re-activated by tectonics associated with the Alpine events far off in southern Europe. Detailed geological maps show surface-breaking faults everywhere, whereas deep coal mining records and onshore seismic reflection surveys reveal many more at depth. A greater population density living on more ‘fragile’ geology may expect considerably more risk from industrially induced earthquakes, should Britain’s recently announced ‘dash’ for shale gas materialise to the extent that its sponsors hope for.

Nicholas van der Elst and colleagues’ paper indicates further cause for alarm. They demonstrate that large remote earthquakes. In the 10 days following the 11 March 2011 Magnitude 9.0 Sendai earthquake a swarm of low-energy events took place around waste injection wells in central Texas, to be followed 6 months later by a larger one (4.5 local magnitude). Similar patterns of injection-related seismicity followed other distant great earthquakes between 2010 and 2012. Other major events seem not to have triggered local responses. The authors claim that the pattern of earth movements produced by such global triggering might be an indicator of whether or not fluid injection has brought affected fault systems to a critical state. That may be so, but it seems little comfort to know that one’s home, business or community is potentially to be shattered by intrinsically avoidable seismic risk.

Wastewater, Seismic Activity, and Fracking Facts (theenergycollective.com)

Africa-Europe exchange of faunas in the Late Miocene

Published on July 15, 2013 by zooks777Leave a comment

The extremely hazardous seaway through the Straits of Gibraltar and the waterless deserts of the Levant presented considerable barriers to natural exchange of animal groups between Africa and Eurasia throughout the period of hominin evolution known from the African Pliocene and Pleistocene record. These barriers were breached by hominins only occasionally. Through most of the Miocene and back to the Mesozoic Era Iberia and what is now Morocco were separated by a wide seaway preventing faunal exchange. That Betic Seaway eventually closed with the tectonic collision of the two sides to form the modern Betic Cordillera in southern Spain towards the end of the Miocene. This left parts of the Mediterranean to evaporate during what is known as the Messinian Salinity Crisis, which reached completion at 5.59 Ma. Yet this Europe-Africa connection was short-lived, being breached by what is regarded as one of the most dramatic events in Cenozoic history: the Zanclean Flood. At 5.33 Ma the Atlantic burst through what is now the Straits of Gibraltar to refill the Mediterranean Basin within a period between a few months and two years. The flooding began as a vast system of rapids some 1 km high with an estimated flow a thousand times that of the modern Amazon.

During the existence of the Europe-Africa land bridge it was possible for animals to move between north-west Africa and western Europe. Evidence that such an exchange did take place comes from a number of Late Miocene localities in southern Spain and North Africa. The first recorded migrants into Spain were African gerbils, then evidence mounted for larger animals, including hippos and early camels moving into Europe and a reverse migration of rabbits and mice. One of the Spanish sites (Gibert, L. et al. 2013. Evidence for an African-Iberian mammal dispersal during the pre-evaporitic Messinian. Geology, v. 41, p. 691-694) has allowed precise magnetostratigraphic dates to be put on the migrations. The Spanish-US team suggests conditions ripe for migration were in three distinct phases: around 6.3 Ma when hippos managed to swim to Europe; around 6.2 Ma which saw European small mammals making the journey south and camels moving to Europe; in a 300 ka window of opportunity from 5.6 to 5.3 Ma for African mice to make the journey into Europe. Several distinct episodes probably reflect some ups and downs of sea level related to glacial retreats and advances in Antarctica.

One implication of the short-lived Messinian land bridge is that it may have been followed by primates, though evidence has yet to be found. A particularly interesting genus, suggested by some as a possible common ancestor for hominins and chimpanzees, is Oreopithecus a bipedal ape recorded from the Miocene of Italy

Afar: the field lab for continental break-up

Published on July 8, 2013 by zooks777Leave a comment

The Afar Depression of Ethiopia and Eritrea is a feature of tectonic serendipity. It is unique in showing on land the extensional processes and related volcanism that presage sea-floor spreading. Indeed it hosts three rift systems and a triple junction between the existing Red Sea and Gulf of Aden spreading centres and the East African Rift System that shows signs of future spalling of Somalia from Africa. Afar has been a focus of geoscientific attention since the earliest days of plate theory but practical interest has grown rapidly over the last decade or so when the area has become significantly more secure and safe to visit. Two recent studies seem to have overturned one of the most enduring assumptions about what drives this epitome of continental break-up.

Perspective view of the Afar depression and en... — Simulated perspective view of the Afar depression from the south (credit: Wikipedia)

From the obvious thermal activity deep below Afar, linked with volcanism and high heat flow, a mantle host spot and rising plume of deep mantle has been central to ideas on the tectonics of the area. A means of testing this hypothesis is the use of seismic data to assess the ductility and temperature structure of deep mantle through a form of tomography. The closer the spacing of seismic recording stations and the more sensitive the seismometers are the better the resolution of mantle structure. Afar now boasts one of the densest seismometer networks, rivalling the Earthscope USArray. http://earth-pages.co.uk/2009/11/01/the-march-of-the-seismometers/ and it is paying dividends (Hammond, J.O.S. and 10 others 2013. Mantle upwelling and initiation of rift segmentation beneath the Afar Depression. Geology, v. 41, p. 635-638). The study brought together geoscientists from Britain, the US, Ethiopia, Eritrea and Botswana, who used data from 244 seismic stations in the Horn of Africa to probe depths down to 400 km with a resolution of about 50 km.

The tomographic images show no clear sign of the kind of narrow plume generally aasociated with the notion of a ‘hot spot’. Instead they pick out shallow (~75 km depth) P- and S-wave low-velocity features that follow the axes of the three active rift systems. The features coalesce at depth; in some respects the opposite of a classic plume that has a narrow ‘stem’ that swells upwards to form a broad ‘head’. If there ever was an Afar Plume it no longer functions. Instead, the rifts and associated lithospheric thinning are associated with a mantle upwelling that is being emplaced passively in the space made available by extensional tectonics. This is closely similar to what goes on beneath active and well-established mid-ocean spreading centres where de-pressuring of the rising mantle results in partial melting and basaltic magmatism along the rift system. Perhaps this is a sign that full sea-floor spreading in Afar is imminent, at least on geological timescales.

Simplified geologic map of the Afar Depression. (credit: Wikipedia after Beyene and Abdelsalam (2005))

For once, mantle geochemists and geophysicists have data that support a common hypothesis (Ferguson, D.J. and 8 others 2013. Melting during late-stage rifting in Afar is hot and deep. Nature, v. 499, p. 70-73). This US-British-Ethiopian team compares the trace element geochemistry of Recent basaltic lavas erupted along the axis of the Afar rift that links with the Red Sea spreading centre with equally young lavas from volcanoes some 20 km from the axis. Both sets of lavas are a great deal more enriched in incompatible trace elements that are generally enriched in melt compare with source than are ocean-floor basalts sampled from the mid-Red Sea rift. Modelling rare-earth element patterns in particular suggests that partial melting is going on at depths where garnet is stable in the mantle instead of spinel. This suggests that a strong layer, about 85 km down in the upper mantle is beginning to melt – magmas formed by small degrees of partial melting generally contain higher amounts of incompatible trace elements than do the products of more extensive melting. Estimates of the temperature of melting from lavas extruded at the rift axis than off-axis are significantly higher than expected at this depth suggesting that deeper mantle is rising faster than it can lose heat.

The depth of melting tallies with the thermal feature picked out by seismic tomography. The two teams converge on passively induced upwelling of hot asthenosphere while the Afar lithosphere is slowly being extended. The degree of melting beneath Afar is low at present, so that to become like mid-ocean ridge basalts a surge in the fraction of melting is needed. That would happen if the strong mantle layer fails plastically so that more asthenosphere can rise higher by passive means. The geochemists persist in an appeal to an Afar Plume for the 30 Ma old flood basalts that plaster much of the continental crust outside Afar. Those plateau-forming lavas, however, are little different in their trace element geochemistry from off-axis Afar basalts. Yet they are not obviously associated with an earlier episode of lithospheric extension and passive mantle upwelling. Most geologists who have studied the flood basalts would agree that they preceded the onset of rifting but have little idea of the actual processes that went on during that mid-Oligocene volcanic cataclysm.

Early humans could probably kill at a distance

Published on June 30, 2013 by zooks7773 Comments

It is always refreshing when physical anthropologists perform experiments as well as pondering on bones. It turns out that examining the bio-mechanics of college baseball players can provide useful clues about where in fossil anatomy to look for signs of potential big-game hunters. Anyone who can hurl a baseball, or one of the smaller but much harder red ones preferred by non-Americans, at speeds exceeding 100 kph could in all likelihood bring down a substantial prey animal with a rock and even more so with a spear. At the heart of an important examination of what our forebears might have done to get a meaty meal (Roach, N.T. et al. 2013. Elastic energy storage in the shoulder and the evolution of high-speed throwing in Homo. Nature, v. 498, p. 483-486) is a US-Indian team’s sophisticated study of college baseball players’ throwing action using high-speed video, radar and precise timing techniques.

Matt Kata throwing for the Houston Astros (Photo credit: Wikipedia)

It seems that there are several physiological phases in demon ball throwing: rotation of the torso; rotation flexion and extension of the shoulder; flexion and extension of the elbow; and wrist extension. All of these contribute to acceleration of the ball before release. While the thrower steps forward the arm is cocked so that ligaments, tendons and muscles crossing the shoulder become stretched, thereby storing energy. During the acceleration phase the bend in the elbow is snapped straight adding yet more power. Readers should note the difference between this action and that of a bowler in cricket, where the elbow snap is banned on pain of severe penalty and public humiliation of the bowler who ‘chucks’. Since a fast bowler also adds energy by running into the crease, this is a humanitarian aspect of the Rules of cricket, although several legal West Indian bowlers of the past 40 years are still remembered with terror by their batsmen contemporaries. No such stricture is placed on the baseball pitcher who has no run-up.

These observations focus attention on the structure of shoulder and elbow, yielding a robust means of predicting how fast throwers with different configurations may have thrown objects. Chimpanzees make poor players of ball games, although they will throw the odd stick, but just for aggressive show. The same goes for the earliest hominins for which we have suitable fossil material: australopithecines may occasionally have eaten carrion but they couldn’t throw rocks or spears with enough force to bring down anything and their throwing range would have been pathetic. Not so Homo erectus! They were well equipped in the hurling department and could, were they so inclined, have hunted equally as well as modern humans. Interestingly, earlier hominins had some of the physiological necessities of decent throwing, but not all of them. So it seems that the full combination emerged in the evolution of our own genus around 2 Ma ago,

This is in contrast to a view held by some anthropologists, such as Christopher Boehm of the University of Southern California, that big game hunting using projectile weapons emerged only with anatomically modern humans after 250 ka, and most likely only reached its acme 45 ka ago. That assumption, at least by Boehm, is central to notions of how social activities centred on meat sharing may have helped evolve morals, such as altruism and shame (see Boehm, C. 2012. Moral Origins: The Evolution of Virtue, Altruism and Shame. Basic Books, New York). That H.erectus would have been able to harness sufficient energy to kill at a distance casts doubt on such assertions. Mere foraging does not require throwing-capable physiology, so how it evolved in early humans with neither the inclination nor bodies to at least begin throwing projectiles at potential prey is something that school might consider.

Right down the middle, explained (news.harvard.edu)
Pitchers have mammoth-hunting ancestors to thank for their prowess (guardian.co.uk)
Origins of human throwing unlocked (bbc.co.uk)

Arctic climate in the run-up to the Great Ice Age

Published on June 30, 2013 by zooks777Leave a comment

Around 3.6 Ma ago a large extraterrestrial projectile slammed into the far north-east of Siberia forming crater 16 km across. The depression soon filled with water to form Lake El’gygytgyn, on whose bed sediments have accumulated up to the present. A major impact close to the supposed start of Northern Hemisphere glacial conditions was a tempting target for coring: possibly two birds with one stone as the lowest sediments would probably be impact debris and boreal lake sediments of this age are as rare as hens’ teeth. The sedimentary record of Lake El’gygytgyn has proved to be a climate-change treasure trove (Brigham-Grette, J and 15 others 2013. Pliocene warmth, polar amplification, and stepped Pleistocene cooling recorded in NE Arctic Russia. Science, v. 340, p. 1421-1426).

El'gygytgyn, Russia, is a impact crater with a... — Lake El’gygytgyn impact crater. (credit: Wikipedia)

The team of US, Russian, German and Swedish scientists discovered that the sedimentary record was complete over a depth of 318 m and so promised a high resolution climate record. The striking feature of the sediments is that they show cyclical variation between five different facies, four of which are laminated and so preserve intricate records of varying weathering and sediment delivery to the lake. The sediments also contain pollens and diatom fossils, and yield good magnetic polarity data. The last show up periods of reversed geomagnetic polarity, which provide age calibration independent of relative correlation with marine isotope records.

A host of climate-related proxies, including pollen from diverse tree and shrub genera, variations in silica due to changes in diatom populations and organic carbon content in the cyclically changing sedimentary facies are correlated with global climate records based on marine-sediment stable isotope. These records reveal intricate oscillations between cool mixed forest, cool coniferous forest, taiga and cold deciduous forest, with occasional frigid tundra conditions through the mid- to late Pliocene. Compared with modern conditions NE Siberia was much warmer and wetter at the start of the record. Around the start of the Pleistocene sudden declines to cooler and drier conditions appear, although until 2.2 Ma ago average summer conditions seem to have been higher that at present, despite evidence from marine proxies of the onset of glacial-interglacial cycles in the Northern Hemisphere.

In detail, Lake El’gygytgyn revealed some surprises including rapid onset of a lengthy cold-dry spell of tundra conditions between 3.31 to 3.28 Ma. The first signs that the lake was perennially frozen appear around 2.6 Ma, well before evidence for the first continental glaciation in North America, presaged by signs around 2.7 Ma that winters consistently became colder than present ones. Overall the lake record presents a picture of a stepped shift in climate in the run-up to the Great Ice Age. Lake El’gygytgyn seems set to become the standard against which other, more patchy records around the Arctic Ocean are matched and correlated. Indeed it is the longest and most detailed record of climate for the Earth’s land surface, compared with 120 and 800 ka for the Greenland and Antarctic ice-caps.

Modelling their findings against likely atmospheric CO₂ levels the authors provide grist to the media mill which focuses on how the late Pliocene may be a model for a future warm Earth if emissions are not curtailed, with visions of dense polar forests

Arctic Once Had a Green Forest and May Have it Again: Study (latinospost.com)
Arctic Tundra ‘Will Turn to Forest’ (truthdig.com)
Weekend Wonk Bonus: Sobering Sediments from Lake E (climatecrocks.com)

In the mantle wet may not imply soft

Published on June 17, 2013 by zooks777Leave a comment

For half a century the Earth’s planetary dynamism – plate movements, mantle convection and so on – has been ascribed to its abundance of water. Experiments on the ductility of quartz seemed to show that it became much weaker under hydrous conditions, and that was assumed to hold for all common silicates, a view backed up by experiments that deformed minerals under varying conditions. It was widely believed that even a few parts per million in a rock at depth would weaken it by orders of magnitude, a view that increasingly dominated theoretical tectonics on scales up to the whole lithosphere and at different mantle depths. Strangely, the founding assertion was not followed up with more detailed and sophisticated work until the last year or so. Though rarely seen in bulk, the dominant mineral in the mantle is olivine and that is likely to be a major control over ductility at depth, in plumes and other kinds of convection.

Experimental work at the temperatures and pressures of the mantle has never been easy, and that becomes worse the more realistic the mineral composition of the materials being investigated. High-T, high-P research tends to focus on as few variables as possible: one mineral and one variable other than P and T is the norm. This applies to the latest research (Fei, H. et al. 2013. Small effect of water on upper mantle rheology based on silicon self-diffusion coefficients. Nature, v. 498, p. 213-215) but the measurements are of the rate at which silicon atoms diffuse through olivine molecules rather than direct measurements of strain. The justification for this approach is that one of the dominant processes involved in plastic deformation is a form of structural creep in which atoms diffuse through molecules in response to stress – the other is ‘dislocation creep’ achieved by the migration of structural defects in the atomic lattice.

Contrary to all expectations, changing the availability of water by 4 to 5 orders of magnitude changed silicon diffusion by no more than one order. If confirmed this presents major puzzles concerning Earth’s mantle and lithosphere dynamics. For instance, the weak zone of the asthenosphere cannot be a response to water and nor can the relative immobility of hotspots. Confirmation is absolutely central, in the sense of repeating Fei et al.’s experiments and also extending the methods to other olivine compositions – magnesium-rich forsterite was used, whereas natural olivines are solid solutions of Mg- and Fe-rich end members – and to materials more representative of the mantle, e.g. olivine plus pyroxene as a minimum (Brodholt, J. 2013. Water may be a damp squib. Nature, v. 498, p. 18-182)

Water is no lubricant (eurekalert.org)

Yes, it was hot during the Permian

Published on June 17, 2013 by zooks7771 Comment

For those of us living in what was the heart of Pangaea – Europe and North America – more than 250 Ma ago this item’s title might seem like the ultimate truism. However, despite our vision of desert dune sands and evaporating inland seas, glaciation blanketed much of the Gondwana part of the supercontinent until the Middle Permian then lying athwart the South Pole. That would go a long way to accounting for extreme dryness at low to mid-latitudes, especially in the deep interior of Pangaea, but just how hot might tropical climates have been? The deglaciation of Gondwana was abrupt and has been touted as an analogue for a possible anthropogenic closure to the Cenozoic glacial epoch that began around 34 Ma in Antarctica and has periodically gripped land at northern latitudes as low as 40°N for the last 2.5 Ma. Since the present distribution of continents is totally different from the unique pole-to-pole shape of Pangaea, that is probably a view that is not widely held by palaeoclimatologists. Nonetheless, getting hard data on Permian conditions has an intrinsic interest for most geoscientists.

One of the best ways of measuring past temperatures, whether surficial or deep within the crust, almost directly is based on fluids trapped within minerals formed at the time of interest. In Permian strata there is no shortage of suitable material in the form of evaporite minerals, especially common salt or halite. A distinctive chevron-like texture develops in halite that forms at the water-atmosphere interface in playa lakes that dry out every year. When thin sections of samples that contain fluid inclusions are slowly heated the air bubbles trapped in salt during crystallisation gradually homogenise with the other trapped fluids. Based on samples that have formed at the present day under a range of air temperatures, the temperature of homogenisation indicates the prevailing air temperature accurately. So well, in fact, that it is possible to assess diurnal temperature variations in suitable halite crystals.

Results have been obtained from Middle Permian halites in Kansas, USA (Zambito, J.J. & Benison, K.C. 2013. Extremely high temperatures and paleoclimate trends recorded in Permian ephemeral lake halite. Geology, v. 41, p. 587-590). In part of the section studied air temperatures reached 73°C, compared with a modern maximum of 57°C recorded in halites from the playas of Death Valley. Moreover, they exhibit changes of more than 30°C during daily cycles. But that kind of weather is common in other hot dry areas today, such as the Dasht-e Lut in eastern Iran. Also, the full data show crystallisation at lower temperatures (maxima of 30-40°C) in part of the sequence. What is noteworthy is that these data are the first quantitative indicators of weather before the last 2.5 Ma. Since evaporites extend back into the Precambrian, the method will undoubtedly extend accuracy and precision to paleoclimate where only proxies and a modicum of guesswork were previously available.

End-Triassic mass extinction link to CAMP: It’s official?

Published on June 10, 2013 by zooks7771 Comment

Mass extinctions and smaller but significant die-offs in the marine and terrestrial domains have been linked in the geoscientific imagination with many things: asteroid impacts; gamma-ray bursts from distant supernovae; belches of methane from the sea floor; emissions of hydrogen sulfide gas from seawater itself during ocean anoxia events; sea-level changes and more. The most intriguing, since it suggests a causal link between the core-mantle boundary and the biosphere, is the influence of flood basalt events and the gases, both greenhouse and toxic, that they undoubtedly released.

The famous K-T extinction (now K-Pg since the Palaeogene became the Period following the Cretaceous rather than the Tertiary) has swayed back and forth between the Chicxulub impact in Mexico’s Yucatán Peninsula and the flood basalts of the Deccan Traps in western India as likely mechanisms, Chicxulub currently being in pole position. The equally devastating event at the close of the Triassic (at 201 Ma) that presaged the rise of the dinosaurs has had a similar external versus internal causality controversy, both the Rochechouarte crater and the Central Atlantic Magmatic Province being candidates.

Rochechouarte, however, was nowhere near as energetic an event as the Chicxulub impact. The problem is, as with all events for which the weight of evidence points to very short time scales – of the order of tens to hundreds of thousand years, is the dating of candidate causes. Rochechouarte happened at 201±2 Ma: it may or may not have coincided with faunal change. Yet timing of the CAMP flood basalts has hitherto been even more coarsely tagged. This imprecision is not unconnected with the choice of radiometric dating methods, the ⁴⁰Ar/³⁹Ar approach being ‘easy’ and hence popular, but limited in its precision and accuracy. The ‘gold standard’ is zircon U-Pb geochronology that depends on the far greater reluctance of the host mineral to lose either parent or daughter isotopes compared with the feldspars, micas and amphiboles used in many other methods. Zircon still in its igneous parent is crucial: it is so durable that vastly older zircons are often found in sediments. Yet basalts contain few zircons.

Zircon geochronology has now emerged from the CAMP flood basalts of eastern Canada, the Atlantic seaboard of the US and that of Morocco, which has a precision of around 30 ka, one to two orders of magnitude better than other methods (Blackburn, T.J. and 8 others 2013. Zircon U-Pb geochronology links the end-Triassic extinction with the Central Atlantic Magmatic Province. Science, v. 340, p. 941-945). The extinction is defined most readily by a sudden change in fossil pollen and spores, possibly within less than 10 ka, as well as extinction of Triassic marine fauna and large numbers of terrestrial reptile and amphibian taxa followed by diversification of early Jurassic dinosaurs. The oldest CAMP basalts are from Morocco immediately above spores of clearly Triassic age; i.e. before the extinction, whereas the basalt flows in Canada and the eastern US (a mere 3 to 13 ka younger)are above the turnover. So, the start of the CAMP flood volcanism brackets the extinction.

But did CAMP cause, indeed could it have caused the extinction? Blackburn and colleagues cannot be certain. A negative carbon-isotope spike associated with the extinction is estimated to have required almost a million km³ of magma to have been erupted almost instantaneously to inject excess CO₂ into the atmosphere. The dating suggests four major pulses of eruption in the areas studied spread over around 600 ka, the last three being associated with biological diversification and recovery in the earliest Jurassic. In fact the research seems merely to suggest strongly that flood volcanism accompanied the extinction, but leaves its causing the death toll still an open question.

The CAMP events marked the beginning of Pangaea’s break-up and the formation of Tethys separating Eurasia and North America from the old Gondwana continental mass. That tropical seaway became the site of massive production of marine carbonates, presumably to draw down any carbon dioxide excess in the atmosphere.

The Top 5 Extinctions (danniteboul.wordpress.com)
What really happens in a flood basalt eruption
(Geological Society of London blog)

Review of fracking issues

Published on May 31, 2013 by zooks7771 Comment

The release and exploitation of natural gas from shales using the unconventional means of in situ hydraulic fracturing – ‘fracking’ – has had plenty of bad press, including some hammering in Earth Pages. Now, what seems to be a balanced academic review has appeared on-line in Science magazine (Vidic, R.D. et al. 2013. Impact of shale gas development on regional water quality. Science, v. 340, DOI: 10.1126/science.1235009). The review focuses on hazards to groundwater resources from a variety of environmental effects, primarily gas migration, contaminant transport through induced and natural fractures, wastewater discharge, and accidental spills.

English: Protests against shale gas drilling i... — Protests against shale gas drilling in Bulgaria (credit: Wikipedia)

Much attention has centred on faulty seals put in place to stop gas escaping from drill targets. Yet fewer than 3% of seals are said to have proved problematic, with some finger-pointing at natural gas leakage from the hydrocarbon-rich shales. After all, there are plenty of natural fractures and completely ‘tight’ stratigraphic sequences are rare. in fact toxic effects of natural gas leakage on surface vegetation have been widely used as exploration indicators for conventional petroleum. The review does point out that there are so few pre-drilling studies of natural leakage that this controversy – including widely publicised blazing household water supplies – can not yet be resolved. Obviously more independent monitoring of areas above prospective shales are essential; but who will fund them? The one well-documented before-and-after study, from 48 water wells in Pennsylvania, USA, showed no change, though it seems that monitoring after fracking was short-lived.

The chemically-charged water used to induce the hydrofracturing obviously leaves an unmistakable mark when leaks occur, and there have been cases of considerable environmental release. The fluids are indeed a wicked brew of acids, organic thickeners, biocides, alkalis and inorganic surfactants, to name but a few infredients. To some extent re-use of such fluids, which are costly, ought to mitigate risks. However, once a shale-gas field is fully developed, large volumes of the fracking fluids remain in the subsurface and may leak into shallow groundwater sources. But what pathways do these fluids follow when they are pumped into shales under very high pressure? The review warns of the lesson of toxic fluid leakage from underground coal mines.

The University of Pittsburgh team who compiled the review usefully outline why shale gas is both profitable and feasible. They deal with what methane does in an environmental chemistry sense. It isn’t a solvent, so carries no other materials such as toxic ions, but its interaction with bacteria creates reducing conditions. A now well-known hazard of subsurface reduction is dissolution of iron hydroxide, naturally an important component of many rocks, that can adsorb a great range of dangerous ions at potentially high concentrations, including those involving arsenic. Reductive dissolution lets such ions loose into natural waters, even at shallow depths. Yet methane is emitted by a host of sources other than hydrocarbon-rich shale: landfill; swamps; other bacterial action; conventional petroleum fields both active and abandoned; and even deep water boreholes themselves. A recent study of groundwater geochemistry in relation to fracking in Arkansas, USA (Warner, N.R. et al. 2013. Geochemical and isotopic variations in shallow groundwater in areas of the Fayetteville shale development, north-central Arkansas. Applied Geochemistry, v. 33, doi/10.1016/j.apgeochem.2013.04.013) does address changes in groundwater chemistry, but not for all the ions cited by the WHO as potential hazards.

Whereas the mechanisms involved in vertical and lateral migration of subsurface fluids are well understood there is little knowledge of natural structural features such as deep jointing, fractures and fault fragmentation that control actual migration from area to area. The use of natural seepage as an exploration guide was largely abandoned when many studies showing apparently high-priority targets proved to be far removed from the actual source of the moving fluids. The most easily investigated route for leakage is the actual ‘plumbing’ that fracking uses. This is held together by cement that high pressures can disrupt before it sets, resulting in leaks. A lot depends on ‘due diligence’ deployed by the contractors, whose regulation can leave a lot to be desired. Vidic and colleagues devote most space to the matter of wastewater and deep formation water, yet make little if any case for routine geochemical monitoring of domestic groundwater supplies in shale-gas fields. Much is directed at the industry itself rather than independent surveys.

German brewers worry fracking will compromise beer quality (cbc.ca)
What the frack do we know? Not much, it turns out (grist.org) Somewhat-over-the top video clip
Shale Gas Fracking Has No Impact on Groundwater in Arkansas, Study Concludes (dailyfusion.net)
Fracking can be done safely, but will it be? (news.yahoo.com)

Bling from space

Published on May 31, 2013 by zooks777Leave a comment

People have a keen eye for unusual objects and an even keener one for the aesthetic. Fossil echinoderms with their five-fold starry shape have been enduringly popular as trinkets since the Palaeolithic. Astonishingly, the gravel terrace at Swanscombe that yielded skull fragments of 400 ka Homo erectus plus many Acheulean tools also contained a flint bi-face ‘hand axe’ with a near perfect echinoid in its blunt grip. It cannot be proven, but the object seems to refute the idea that an artistic sense only arose with anatomically modern humans in the last 100 ka. Our immediate ancestors of the Neolithic sometimes took collecting to extremes in graves half full of fossil sea urchins (McNamara, K.J. 2007. Shepherds’ crowns, fairy loaves and thunderstones: the mythology of fossil echinoids in England. In: Piccardi, L. & Masse, W.B. Myth and Geology. Geological Society, London, Special Publication 273, 279–294).

Before the invention of metal smelting native gold, iron and copper appear in the archaeological record, undoubtedly because they look and indeed feel so different from the usual pebbles on the beach or just lying around. It is just that element of the odd that continues to draw people, including scientists, into a perpetually stooped posture when the walk across surfaces scattered with pebbles and boulders. The habit is especially hard to shake off for the meteoriticist whose hunting grounds are desert plains and ice caps where oddities are easy to spot, even when rare. So it is interesting when such dogged searchers encounter evidence of long-dead people having done much the same.

By 5300 years ago people had settled in small farming communities in the Nile Valley eventually to develop on the shores of lake – now represented by several smaller water bodies – what is regarded as the world’s first city near modern Faiyum. These Predynastic people buried their dead nearer to the Nile at Gerzeh, often sending them off with grave goods. The site has been continually excavated by professional archaeologists for more than a century, beginning with Sir Flinders Petrie. Two of the graves contained metallic iron beads, which presented a puzzle as iron smelting is only known from the 6^th century BCE onwards. Unsurprisingly, the beads came to be regarded as artefacts wrought from an iron meteorite, though their highly altered nature and intrinsic value thwarted attempts at full analysis. Geochemists from the Open and Manchester Universities, and the Natural History Museum have now resolved the issue (Johnson, D. et al. 2013. Analysis of a prehistoric Egyptian iron bead with implications for the use and perception of meteorite iron in ancient Egypt. Meteoritics and Planetary Science, on-line, DOI: 10.1111/maps.12120). Non-destructive electron microscopy and X-ray tomography reveal, respectively, clear signs of the banded Widmanstätten structures and traces of nickel-rich iron alloy (taenite) that typify iron meteorites but are absent from smelted iron. The beads were clearly beaten and rolled into shape, but this working did not destroy the tell-tale evidence of their origin.

Optical, microprobe and CT-scan images of Predynastic iron bead from the Nile Valley (credit: Open University)

This provenance tallies with the appearance in early New Kingdom hieroglyphs of the term biA-n-pt – literally iron-from-the-sky – which was adopted for smelted iron when first made in the 26 to 27^th Dynasties. But pharaonic iron was not a poor relation of gold, regarded as flesh of the gods and hence featuring in the masks of Pharaohs such as Tutankhamen, but supposedly what their bones were made from.

Ancient Egyptian Beads Made From Meteorites (natureworldnews.com)
Iron in Egyptian relics came from space (worldduh.com)

Continental comfort blanket

Published on May 22, 2013 by zooks777Leave a comment

Way back in the mists of time, say around 1970-71, an idea was doing the rounds that because the thermal conductivity of continental crust is lower than that of the ocean floor it should allow thermal energy to build up in the mantle beneath. In turn that might somehow encourage the formation of hot spots and a shallower depth to the asthenosphere: the outcome might be to encourage rifting of weakened lithosphere and ultimately a new round of sea-floor spreading. The case often cited was the Atlantic – North and South – since there are eight hotspots currently on the mid-Atlantic ridge. Africa was another popularised case with a great many broad domes associated with Cenozoic volcanism, and the link between formation of the East African Rift System, hot spots and doming had already been suggested. Africa has barely drifted for around 100 Ma and the domes were supposed to have formed by the build up of heat in the mantle beneath. Geoscience moved on to clearly demonstrate the coincidence of large igneous provinces and flood basalt volcanism with the initiation of Atlantic spreading in the form of the Central Atlantic and Brito-Arctic LIPs during initial opening of the South and North Atlantic at the end of the Triassic and during the Palaeocene respectively. But the role of continental insulation became a bit of backwater compared with notions of mantle plumes emanating at the core-mantle boundary. Well, it’s back.

There is now a vast repository of ocean-floor lavas that formed at mid-ocean ridges in the past, thanks to the international Deep Sea and Ocean Drilling Programmes begun in 1968 about when the heyday of plate tectonics really got underway. In the last 45 years there have also been great advances in igneous geochemistry and its interpretation, including relations with mantle melting temperatures. Geochemists at the Friedrich-Alexander-Universiteit in Erlangen, Germany have re-examined the major-element geochemistry of 184 glassy ocean-floor basalts from drill sites of different ages on the floor of the Atlantic Ocean and compared them with 157 from the Pacific. To avoid the possible influence of plume-related heating, the sites were chosen well away from the tracks of existing hot spots. Mantle temperature can be assessed from the sodium and iron content of basalts, Na decreasing with higher temperatures and Fe doing the reverse (Brandl, P.A. et al. 2013. High mantle temperatures following rifting cause by continental insulation. Nature Geoscience, v. 6, p. 391-394). Atlantic samples show increasing Na and decreasing Fe contents in progressively younger basalts, i.e. a trend with time of decreasing mantle temperature such that the oldest (~166 Ma) record 150°C higher mantle temperature than the youngest, with a similar result for the Indian Ocean floor. No such trend is present in samples from the same age range of the Pacific Ocean floor. At around 170 Ma the mid-Atlantic Ridge was close to the continental lithosphere of the Americas and Africa, whereas the East Pacific Rise was at least 2000 km from any continental margin. Younger Atlantic samples formed progressively further from its shores record cooling of the mantle source.
A prediction of the model is that the converse, continental accretion to form supercontinents such as Pangaea, should rapidly have caused considerable warming in the mantle beneath them. This suggests that the formation of supercontinents, or even less substantial continents, should carry the seeds of their re-fragmentation, as Africa is currently demonstrating by the separation of Arabia since the Red Sea began to open some 15 Ma ago, which Somalia and much of eastern Kenya and Tanzania seem destined to follow once the East African Rift System ‘gets steam up’.

Langmuir, C. 2013. Older and hotter. Nature Geoscience, v. 6, p. 332-333

Could the Toba eruption have affected migrating humans?

Published on May 9, 2013 by zooks7771 Comment

Around 73 thousand years ago a supervolcano in Sumatra erupted on a scale unprecedented in the last 2 million years. It left a 100 by 30 km elliptical caldera now occupied by Lake Toba, and explosively ejected 2800 of magma, about 800 km³ falling as ash as far afield as the Greenland ice cap. Although ice-core records show little if any sign of associated climate change in polar regions, the vast amount of ash and sulfate aerosols blasted into the stratosphere must have had some ‘global winter’ effect. Large areas of South Asia were blanketed by thick beds of ash. Human migration from Africa into Eurasia was probably underway at the time, indeed stone tools are found directly beneath and above the Toba ash in southern India and Malaysia. Some palaeoanthropologists have seen the stresses imposed by the Toba eruption as possible means of reducing the entire human population to a mere few thousand: a genetic ‘bottleneck’ that could have led to rapid evolution among surviving generations that may have shaped changes in human behaviour and culture.

There is a widening range of views on the climate changes that may have followed Toba. It has even been suggested that global mean surface temperature fell by as much as 10°C (Robock, A. et al. 2009. Did the Toba volcanic eruption of ∼74 ka B.P. produce widespread glaciation? Journal of Geophysical Research: Atmospheres, v. 114, DOI: 10.1029/2008JD011652), although not so far as to produce a worldwide glacial surge but sufficient to devastate vegetation. This bleak look back to a critical point in human affairs resulted from modeling of the effects of a global reflective cloud of ash and sulfate. A later modeling study factored in particle and aerosol sizes (Timmreck, C. et al. 2010. Aerosol size confines climate response to volcanic super-eruptions. Geophysical Research Letters, v. 37, doi:10.1029/2010GL045464) to give a less dramatic, but still severe maximum global cooling due to Toba of ~3.5°C.

The focus has now shifted from modelling to a more direct look at the environmental effects of the Toba super-eruption, preserved in sediments beneath Lake Malawi in southern Africa (Lane, C.S. et al. 2013. Ash from the Toba supereruption in Lake Malawi shows no volcanic winter in East Africa at 75 ka. Proceedings of the National Academy of Science, v. 110, doi/10.1073/pnas.1301474110). The sediments contain a thin ash layer that is very different from those produced by East African Rift volcanism but chemically and texturally similar to the Toba ash from the Indian Ocean and India. The sediments, diatom fossils and chemical biomarkers immediately above the ash show little sign of a significant temperature fall. At most it records a 1.5°C fall, and the authors conclude little chance of a human genetic bottleneck among Africans living at the time.

There is clearly a conflict between results of modeling and real-world climatic data, which is interesting in its own right. But the Malawi findings do not rule out ‘bottlenecks’ resulting from severe stress in South Asia where the ash itself would have severely affected game and vegetation for long enough to face migrating human bands with the prospect of starvation. Obviously, some survived to move on and to leave their tools behind on top of the Toba Ash.

Supervolcano eruptions may not be so deadly after all (newscientist.com)
Our Past (and Future) With Supervolcanoes (theratchet.ca)
Volcano catastrophe idea ‘dismissed’ (bbc.co.uk)

Australopithecus sediba: is she or is she not a human ancestor?

Published on April 22, 2013 by zooks777Leave a comment

The remarkable find of two well-preserved skeletons of a 2 Ma hominin in a South African cave in 2008 and publication of their preliminary analysis in 2011 seemed set to shake up human origins research. There was a more or less complete hand – indeed an entire arm and shoulder – a lower leg with ankle bones, a near-complete head and lots more besides. Most was from one female individual, but significant bits from two others that allowed a well-supported reconstruction of the new species Au. sediba. The discoverer, Lee Berger of The University of the Witwatersrand, South Africa (well he initiated the dig, but his young son found the first critical material) is so excited 5 years on that he uses hip-hop phraseology, she ‘got swag’, presumably assuming that means pretty cool (Gibbons, A. 2013. A human smile and funny walk for Australopithecus sediba. Science, v. 340, p. 132-133), but on the street there are other meanings and attitudes towards the phrase and unwary use is not advised.

More details now have emerged in a special issue of Science introduced by Berger in less fulsome language (Berger, L.R. 2013. The mosaic nature of Australopithecus sediba. Science, v. 340, p. 163). As the title suggests, the surprise lies in almost every critical part of the species. Although the spine shows curvature (lordosis) needed for an animal evolved from a quadruped to bipedality in order to balance when upright, the ankle bone is unlike the flat-based human one, being pointed as is that of chimpanzees. As a result walking would have involved an unusual and perhaps unsteady gait; the individuals did fall over into a death pit and one commentator thought the gait might have seemed ‘provocative’. An unusual knee bone is thought to be an evolved countermeasure to such exaggerated mincing. Despite the very human-like hand, extremely long arms and shoulders remarkably like those of the favoured jacket of a star of the BBC series The Dragons’Den point to habitual clambering in trees. Authors of a report on dentition suggest a close similarity to that of the Au. africanus, living at the same time and also found in the same system of fossil-rich caves north-west of Johannesburg, South Africa. Controversially, the tooth team suggests a closer similarity of both to early Homo species than to earlier australopithecines in East Africa, which would shift the focus of human origins to southern Africa. Counter to that view is a find of 400 ka-older, putative human remains in Ethiopia. Yet they take the form of a lower jaw that resembles that of Au. sediba.

The emerging, more detailed picture is not tidy, as suspected from early examination of the Malapa hominins. One thing is for sure, the South African caves are being swarmed over, which paid dividends in 2011 just 15 km from the Malapa cave with another embarrassment of riches at Sterkfonein in the form of abundant foot bones of a currently un-named species of roughly the same age. Things are beginning to take on an element of national pride, with ‘The Birthplace’ at stake: Kenya, Tanzania, Ethiopia or South Africa?

Australopithecus sediba: human by accident? (evoanth.wordpress.com)
How 2-Million-Year-Old Ancestor Moved: Sediba’s Ribcage and Feet Were Not Suitable for Running (lifebeyondus.wordpress.com)
Our New Most Immediate Ancestor? (news.nationalgeographic.com)

The Time Lords of Geology

Published on April 16, 2013 by zooks777Leave a comment

Epic Time Lord — Time Lord, possibly outside the offices of the International Commission on Stratigraphy (credit: Sorcyress via Flickr)

Because it is the ultimate historical discipline, the essence of geology centres on time, measuring its passage and establishing correlations in time on a global scale so that an interlinked story of Earth evolution can be told. In fact geology is not just about a record of what happened in the four dimensions of place and time; it is a great deal more multidimensional, involving temperature, strain, chemistry, erosion, deposition, sea-level , the course of life and much more besides. Ever more multifaceted and, sadly, divided into subdisciplines and interfaces with other aspects of natural science that few if any individuals can grasp, an almost legally enforceable set of rules is needed to keep the order orderly. Unlike history and more akin to archaeology geological time is of two kinds, its precisely quantitative measure being a relative newcomer.

Since it emerged in the Enlightenment that began in the late 17^th century geology has been dominated by a relative sense of timing: Steno’s Law of Superposition, and those relating to deformation, igneous eructations, erosion and deposition, first addressed systematically by James Hutton, being the most familiar. The notion of an absolute time scale into which events separated relative to one another could be fitted with confidence is a real latecomer. Although first attempted between 1650 and 1654 by Archbishop of Armagh James Ussher – he reckoned from the Old Testament that everything began at dusk on Saturday 22 October 4004 BCE – the only useful and broadly believable approach to absolute time has been based on the decay of radioactive isotopes incorporated into minerals once they had formed within a rock. But that is no panacea for the simple reason that most of them form through igneous or metamorphic processes and only rarely in the course of sedimentation. It also has only become reliable and precise in the last two or three decades.

Tying together global records of all the kinds of process that have made, shaped and changed the Earth has therefore become an increasingly complex blend between local relative dating, burgeoning regional to global means of correlation and the odd point in absolute time. What has arisen is a dual system that, if truth were told, is often used in a cavalier fashion. Equally to the point, the rules have of late become unfit for purpose and are in need of revision, which is a task for the Time Lords, properly known as the International Commission on Stratigraphy (ICS). The trouble is, the rules have themselves evolved somewhat episodically while their subject is appropriately in continual motion and change, if not anarchic. To the outsider things can seem very odd indeed. Most reasonably well-read souls will have heard of the Cambrian and the Jurassic, largely because of the popularity of trilobites that blossomed in the one and dinosaurs that strutted the land in the other. What is less well known is that the two names have different usages as adjectives: one to signify an interval of time called a Period, the other a System of essentially piled-up sedimentary rocks.

There are greater dualisms that group the Period/System divisions: the largest Eon/Eonothem groupings of Archaean, Proterozoic and Phanerozoic; the Era/Erathem signifiers such as Palaeoproterozoic, Mesozoic and Cenozoic. Incidentally, the time between the formation of the Earth and the first palpable rocks, from about 4550 to 4000 Ma, has been called the Hadean but has no designated status, possibly because it has no rock record whatsoever. Divisions of Periods/Systems apply only to the time since fossils became abundant 541 Ma ago, and in order of fineness of division are Epoch/Series and Age/Stage. Example of the first can be Lower, Middle and Upper – to spice things up, Middle maybe omitted from some Periods/Systems – or they might be given names derived from type areas, such as the ever popular Llandovery at the base of the Silurian Period/System. Helpfully, the Cambrian contains Terreneuvian, Series 2, Series 3 and Furongian from early to late/bottom to top. The final global division has always floored undergraduates and shows little sign of relief – there are a great many Ages/Stages, in fact a round 100 (I may have miscounted), 98 with names, 2 currently unnamed and 4 in the Cambrian called Stages 2 to 5: confusing, that… has anyone spoken of the Stage 3 Stage or the Stage 5 Age of the Cambrian?

Worryingly, in my hasty overview of the ICS International Stratigraphic Chart above I have reversed the official designation of chronstratigraphic/geochronological nomenclature: is this likely to have me committed to the geoscientific equivalent of Guantanamo Bay, or merely limbo?

I have by no means exhausted officialise. Readers may not be surprised to learn that the Time Lords have bent Heaven and Earth literally to concretise the double entendres of geology. The base of almost every Age/Stage in the Phanerozoic Eonothem/Eon is defined at a suitably agreed point on the ground by, in a few cases, a real golden spike (I may be mistaken on this, as the only one I tried to visit was at the base of a Welsh cliff suitable only to be visited by – in the timeless phrase – ‘a strong party’). More prosaically there are monuments of various ethically appealing designs that go by the sonorous name Global Boundary Stratotype Section and Point. I have it on reasonably good authority that ICS delegates have, on occasion, needed to be physically restrained from fist fights over which nation shall host a particular GSSP (the ‘B’ in the acronym is aspirated).

This is the point that all readers will have been waiting for: it has been suggested to ICS that the whole edifice is looked at very closely and perhaps revised (Zalasiewicz, J, et al. 2013. Chronostratigraphy and geochronology: A proposed realignment. GSA Today, v. 23 (March 2013), p. 4-8). For professionals this is an obligatory read, for others optional: there is no excuse as it is downloadable for free – click on the title. While you are about it, you can also download from GSA Today the famous proposal for an entirely new series/epoch called the Anthropocene (see also A sign of the times: the ‘Anthropocene’ in EPN issue of May 2011)

Hybridisation in human evolution

Published on April 16, 2013 by zooks777Leave a comment

A press release from the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, announces the completion of the most precise genome from a third Neanderthal individual. For the first time it is possible to distinguish copies of the genes inherited by the individual from both parents. The data release coincided with a review of genetic evidence for interbreeding between early Homo sapiens and other species.

The full item can be read at Earth-logs in the Human evolution and migrations archive for 2013

Modern human migration out of and within Africa relative to the domains of coeval archaic humans 1 = modern humans 2 = Neanderthals 3 = other archaic humans (credit: Wikipedia)

Cordilleran terrane accretion in western North America

Published on April 7, 2013 by zooks7772 Comments

One of the key areas for unravelling the range of tectonic processes involved in the assembly of continents lies in the Western Cordillera of North America, made up of dozens of slivers of mutually exotic terranes. Their exposed upper parts remain largely intact and are dateable using fossils or radiometric dating. Through assiduous palaeomagnetic research it is sometimes possible to chart their motions over time to see the manner in which they approached and collided with one another. Geoscientists are now able to link such a complex process with underlying tectonics, not by inference but through direct seismological observation of the remains of subducted slabs in the mantle deep beneath.

sigloch — The crumpled Farallon Plate beneath North America, colours showing different depths in the mantle (credit: Karin Sigloch)

This item can be read in full at Earth-logs in the Tectonics archive for 2013

Resource snippets

Published on April 3, 2013 by zooks7771 Comment

Wasted natural gas

Much attention has centred on fracking shales to release otherwise locked-in gas, while production of liquid petroleum by the same kind of process is also increasing with little publicity, especially in the US. From a purely economic standpoint wells that yield oil and gas from fractured shale might seem to be quite a boon. Well, they probably are, if the gas can be sold. One of the biggest shale-oil targets is the Late Devonian to Early Carboniferous Bakken Shale in the Williston Basin that stretches across 360 thousand km^2‑ beneath parts of the Dakotas, Wyoming and Montana in the US and Saskatchewan in Canada. This shale is the source rock for most of the conventional oil production from the Williston basin since the 1940s. At the start of the 21^st century direct production of oil from the Bakken began in North Dakota, unleashing a major drilling boom and a ten-fold increase in land-leases for production. The state is now the second largest US oil producer after Alaska warranting a major feature National Geographic. Trouble is North Dakota is not well served by pipelines of any kind and oil is shipped by rail, much as it was in the early days of the US oil industry.

The natural gas released by fracking is simply wasted, partly by flaring at the wellhead but an unknown volume of pure methane is simply vented to the atmosphere. At rough 25 times the greenhouse warming capacity of CO₂ the perverted economics of waste methane is, unsurprisingly, becoming scandalous and increasingly dangerous. Such is the magnitude of shale-gas production in the US the price of natural gas has fallen dramatically so that from the Williston Basin simply carries no profit and therefore has nowhere to go except up in flames or directly to the air. The US Environmental Protection Agency apparently can do little to halt the venting. British onshore source rocks, such as the Upper Jurassic Kimmeridge Shale, which has a hydrocarbon content up to 70% and is regarded as the most important rock in Europe being the source for much of the petroleum beneath the North Sea and other oil provinces, are likely targets for fracking now the UK government has given the go-ahead in a new ‘dash for gas’. Chances are it may become a dash for onshore shale-oil .

Manganese nodules finally tagged for production

Almost 40 years ago my desk was almost buried under tomes of information about dull black nodules looking like blighted potatoes as I worked on the now abandoned Level-2 Open University course on The Earth’s Physical Resources. Made mainly out of manganese and iron minerals they also contain ore-grade amounts of nickel, copper and cobalt together with other metals. Were they beneath the crust they would be mined eagerly, but such manganese nodules litter vast areas at the surface of the oceans’ abyssal plains. Such was their potential that around half a billion dollars was spent on oceanographic and geochemical surveys to map the richest nodule fields. Part of the attraction at a time when the non-renewable nature of conventional metal deposits was touted as a threat to civilisation as we know it, as in The Limits to Growth, was that the nodules were zoned and clearly growing: they appear to be renewable metal resources.

Mining them is likely to be hugely costly: they will have to be dredged or sucked-up from the deep ocean basins; intricate metallurgical methods are needed to separate and smelt the paying metals and the risks of deep-sea pollution are obvious. As with shale gas, the UK Tory premier David Cameron has leapt onto Lockheed Martin UK’s announcement that it is finally profitable to get at the nodules, in the manner of the proverbial ‘rat up a drainpipe’. Cameron believes that the venture to harvest one of the most metalliferous patches on the east Pacific floor off Mexico may rake the UK’s economic potatoes out of the fire to the tune of US$60 billion over the next 30 years. Lockheed Martin is an appropriate leader in this scramble having designed some of the equipment aboard a ship financed by Howard Hughes, the 50 thousand tonne Glomar Explorer. A curious vessel, the Glomar Explorer was widely publicised in the mid-70s as the flagship for a manganese nodule pilot project. In fact it was built to snaffle a Soviet submarine (K-129) and its contents of codebooks, technical equipment and nuclear missiles that sank to the abyssal plains in the Pacific about 2500 km to the north-west of Hawaii. It did grapple the submarine, some cryptographic equipment, a couple of nuclear tipped torpedoes and six of the dead crew members. It is still operational, but as an ultra-deep water drill rig.

We will have to wait to see if nodule mining is a ‘go-er’, and very little information has emerged about methodology. The target metal is probably nickel with its importance in rechargeable batteries, plus rare-earth metals that are in notoriously short supply. Whether or not raking, dredging or sucking-up the nodules will have insupportable environmental impact depends on the amount of on-board processing; the nodules themselves are pretty much insoluble. Extracting and separating the metals will probably involve some kind of solution chemistry rather than the beneficiation common in most on-shore metal mines. Such hydrometallurgy has considerable potential for pollution, unless the raw nodules are shipped to shoreline facilities, at a hefty cost. One thing occurred to me while writing about manganese nodules as a major resource was that their blends of metals would not match the proportions actually required in commerce. On a grand scale their exploitation could well play havoc with currently booming metal prices and drive on-shore mining to the wall. But, to be frank, I think this is a bit of tropical sea-bed bubble fraught with legal tangles connected with the United Nations Convention on the Law of the Sea.

UK firm joins ocean mineral rush (bbc.co.uk)
New subsea mining concepts developed | Mining Australia (oceansnrg.com)
Fracking, North Dakota and U.S. Economic Explosion (247wallst.com)
The Great Fracking Fraud (theburningplatform.com)

Geochemistry and economic history

Published on March 22, 2013 by zooks777Leave a comment

At first reading this item’s title might seem to convey nonsense, yet there is an interesting relationship between these two very different disciplines. It concerns the pillaging of South and Central America by conquistadors who followed Columbus’s pioneering route across the North Atlantic in 1492. Aside from glory their motive was profit, and that was most conveniently concentrated in the form of gold and silver, to be found in abundance among the native people of what came to be known as the Americas. Once such plunder declined silver ores were soon discovered in Peru and Mexico, thereby maintaining the supply. Bullion or plate – so named from the fact that precious metal was most often transported in the form of sheets – was the major cargo of the great treasure ships in the period from 1515 to 1650. It is remembered in such geographic names as the Rio de la Plata separating modern Argentina and Uruguay.

Werner Herzog and Klaus Kinski shooting "... — Klaus Kinski, well into his role as an insane conquistador, disputes the script with director Werner Herzog while shooting “Aguirre, The Wrath Of God” (credit: Flickr p373)

It might seem that when such a vast amount of loot entered Europe the buying power of silver in particular would have fallen to result in inflation in the price of basic commodities, much as printing paper money may have that result nowadays. Indeed, over those roughly 150 years prices increased by as much as five times. Another factor was a tendency for silver supply to be augmented simply by debasing newly minted currency with other metals. Yet another is that over the same period China adopted silver as a money commodity increasing demand and so spurring exploration and advances in metallurgical extraction from new ores. Furthermore, the entire fabric of economy in Europe began to shift as feudalism began to be supplanted by capitalism at the close of Medieval times. The sheer complexity of competing factors has made the so-called ‘Price Revolution’ of the 16^th and 17^th centuries a thorny issue for economic historians. This is where geochemists found that they had a ‘shout’ in what Thomas Carlisle dubbed the ‘dismal science’.

Silver ores also contain lead and copper, which inevitably contaminate silver metal extracted from them. Depending on the processes involved in mineralisation the abundances of both metals vary from mine to mine. More tellingly, so do the relative proportions of the different Pb and Cu isotopes, Pb isotopes reflecting the age of the rocks in which ores are found. Inherited by coinage, the isotopes can be used to assess provenance of coins (Desaulty, A.-M. & Albarede, F. 2013. Copper, lead and silver isotopes solve a major economic conundrum of Tudor and early Stuart Europe. Geology, v. 41, p. 135-138), while the dates embossed on coins at the mint potential chart the course of the bullion trade. Desaulty and Albarede show that silver from the vast Potosí mine in modern Bolivia opened by conquistadors barely shows up in British coinage of the period, which is dominated with Mexican isotopic signatures as well as those from European mines. The latter account almost exclusively for the coinage of the late Medieval period. The conclusion is that the huge potential of Potosí served the needs of Spanish entrepreneurs though a trans-Pacific Spanish trade in which Bolivian silver bought goods from China, including gold. Spanish coins, on the other hand, show little of either Bolivian or Mexican silver, suggesting that Spanish world trade may well have used American bullion directly to purchase goods throughout its sphere of influence centred on the Philippines, while Mexican silver engaged in European trade and also found its way into the British economy by way of the slave trade.

Although Desaulty and Albarede claim to have solved a ‘conundrum’ it seems more likely that their revelations will make historians of post-Medieval economics scratch their heads even more.

Climate change and global volcanism

Published on March 20, 2013 by zooks777Leave a comment

Geologists realized long ago that volcanic activity can have a profound effect on local and global climate. For instance, individual large explosive eruptions can punch large amounts of ash and sulfate aerosols into the stratosphere where they act to reflect solar radiation back to space, thereby cooling the planet. The 1991 eruption of Mt Pinatubo in the Philippines ejected 17 million tones of SO₂; so much that the amount of sunlight reaching the Northern Hemisphere fell by around 10% and mean global temperature fell by almost 0.5 °C over the next 2 years. On the other hand, increased volcanic emissions of CO₂ over geologically long periods of time are thought to explain some episodes of greenhouse conditions in the geological past.

The converse effect of climate change on volcanism has, however, only been hinted at. One means of investigating a possible link is through the records of volcanic ash in sea-floor sediment cores in relation to cyclical climate change during the last million years. Data relating to the varying frequency volcanic activity in the circum Pacific ‘Ring of Fire’ has been analysed by German and US geoscientists (Kutterolf, S. et al. 2013. A detection of Milankovich frequencies in global volcanic activity. Geology, v. 41, p. 227-230) to reveal a link with the 41 ka periodicity of astronomical climate forcing due to changes in the tilt of the Earth’s axis of rotation. This matches well with the frequency spectrum displayed by changes in oxygen isotopes from marine cores that record the waxing and waning of continental ice sheets and consequent falls and rises in sea level. Yet there is no sign of links to the orbital eccentricity (~400 and ~100 ka) and axial precession (~22 ka) components of Milankovitch climatic forcing. An interesting detail is that the peak of volcanism lags that of tilt-modulated insolation by about 4 ka.

At first sight an odd coincidence, but both glaciation and changing sea levels involve shifting the way in which the lithosphere is loaded from above. With magnitudes of the orders of kilometres and hundreds of metres respectively glacial and eustatic changes would certainly affect the gravitational field. In turn, changes in the field and the load would result in stress changes below the surface that conceivably might encourage subvolcanic chambers to expel or accumulate magma. Kutterolf and colleagues model the stress from combined glacial and marine loading and unloading for a variety of volcanic provinces in the ‘Ring of Fire’ and are able to show nicely how the frequency of actual eruptions fits changing rates of deep-crustal stress from their model. Eruptions bunch together when stress changes rapidly, as in the onset of the last glacial maximum and deglaciations, and also during stadial-interstadial phases.

Whether or not there may be a link between climate change and plate tectonics, and therefore seismicity, is probably unlikely to be resolved simply because records do not exist for earthquakes before the historic period. As far as I can tell, establishing a link is possible only for volcanism close to coast lines, i.e. in island arcs and continental margins, and related to subduction processes, because the relative changes in stress during rapid marine transgressions and recessions would be large.. Deep within continents there may have been effects on volcanism related to local and regional ice-sheet loading. In the ocean basins, however, there remains a possibility of influences on the activity of ocean-island volcanoes, though whether or not that can be detected is unclear. Some, like Kilauea in Hawaii and La Palma in the Canary Islands, are prone to flank collapse and consequent tsunamis that could be influenced by much the same process. Another candidate for a climate-linked, potentially catastrophic process is that of destabilisation of marine sediments on the continental edge, as in the Storegga Slide off Norway whose last collapse and associated tsunami around 8 thousand years ago took place during the last major rise in sea level during deglaciation. The climatic stability of the Holocene probably damps down any rise in geo-risk with a link to rapid climate change, which anthropogenic changes are likely to be on a scale dwarfed by those during ice ages.

Further support for Homo floresiensis (the ‘hobbit’)

Published on March 15, 2013 by zooks777Leave a comment

When they were first discovered in Liang Bua cave on the Indonesian island of Flores diminutive hominin remains sparked off a heated debate. Part of the reason for dispute was the age of the deposit in which they were found (18 to 850 ka), so young that it indicated possible cohabitation on the island with anatomically modern humans. On the one hand, the finders claimed that they represented a previously unknown hominin species. Other specialists considered that the tiny size (adults no taller than about a metre with brain capacity around that of australopithecines) indicated some congenital dwarfism.

In the 9 years since the remains came to light, several anatomically features have been cited to support the view of a distinct hominin species: their lack of a chin and different arm and shoulder anatomy, which H. floresiensis shares with H. erectus and H. georgicus. The fossils are associated with simple stone tools and bones of a variety of prey animals that show cut marks and charring, suggesting that cooking was part of these hominins’ lifestyle; despite having small brains they were not unintelligent.

Substantial remains of nine or more individuals have been unearthed so that anatomical detail is almost complete. In 2007 details were published of three well-preserved wrist bones from the original find. They too were sufficiently different from modern and Neanderthal humans to warrant confirmation that H. floresiensis is indeed a distinct hominin species. Further work on wrist bones from other individuals has now more or less put the seal on this identity (Orr, C.M. et al. 2013. New wrist bones of Homo floresiensis from Liang Bua (Flores, Indonesia). Journal of Human Evolution, v. 64, p. 109-129), the authors concluding that ‘The pattern of morphology … supports H. floresiensis as a valid taxon and refutes the hypothesis that these specimens represent modern humans with some kind of pathology or growth disturbance’. They take matters further by suggesting that their lineage was established before divergence of modern humans and Neanderthals. As with the shoulder morphology that of their wrists would have somewhat hindered tool-making dexterity, but nonetheless they did make tools.

Global groundwater depth

Published on March 11, 2013 by zooks777Leave a comment

The single most vital resource for human survival is clean, fresh drinking water. For a large proportion of the world’s population that right is not guaranteed, with harrowing consequences especially for children under 5-years old. Without careful processing surface water can only rarely be assumed fit to drink, especially in areas with dense populations of people, livestock or wildlife. Groundwater, on the other hand, has generally passed through aerated upper soil layers before it ended up below the water table in an aquifer. In that passage it is filtered and subject to various oxidising processes, both chemical and organic, that renders it a great deal more free of pathogens than standing or running surface water. Remarkably, a common mineral in any oxidised soil horizon is goethite, an iron hydroxide, which is capable of adsorbing a variety of potentially damaging ions. So, of all fresh water that stored beneath the surface is the safest for people to drink.

By its very nature groundwater is hidden and requires both geological exploration and the drilling or digging of wells before it can become a resource. Areas underlain by simple stratiform sediments or lava flows present far less of a challenge than do geological settings with complex structures or that are dominated by ancient crystalline basement rocks. Time and again, however, crises in water supply arise from drought or sudden displacements of populations a great deal faster than the pace of groundwater exploration or development needed to cope with shortages. Were the potential for subsurface supplies known beforehand relief would be both quicker and more effective than it is at present.

Image of simulated depth to water table for Africa (Courtesy of Y. Fan, Rutgers University, USA)

Thanks to three geoscientists from Rutgers University, USA and the University of Santiago de Compostela, Spain, (Fan, Y et al. 2013. Global patterns of groundwater table depth. Science, v. 339, p. 940-943) a start has been made in quantifying the availability of groundwater worldwide. They have modelled how the likely depth of the water table may vary beneath the inhabited continents. As a first input they digitised over 1.5 million published records of water table depths. Of course, that left huge gaps, even in economically highly developed areas. There is also bias in hydrogeological data towards shallow depths as most human settlements are above easily accessible groundwater.

To fill in the gaps and assess the deeper reaches of groundwater Fan et al. adapted an existing model that assumes groundwater depth to be forced by climate, topography and ultimately by sea-level. It is based on algorithms that predict groundwater flow after its infiltration from the surface. Such an approach leaves out drawdown by human interference and is at a spatial resolution that removes local complexities. The influence of terrain relies on the near-global elevation data acquired by NASA’s Shuttle Radar Topography Mission (SRTM) in February 2000, resampled to approximately 1 km spatial resolution, supplemented by the less accurate Japan/US ASTER GDEM produced photogrammetrically from stereo- image pairs. Other input data are assumptions about variation in hydraulic conductivity, which is reduced to a steady decrease with depth, models of infiltration from the surface based on global rainfall and evapotranspiration patterns and those of surface drainage and slopes. No attempt was made to input geological information

The results have been adjusted using actual water-table depths as a means of calibration across climate zones on all inhabited continents. The article itself is not accessible without a Science subscription, but the supplementary materials that detail how the work was done are available to the public, and include remarkably detailed maps of simulated water table depths for all continents except Antarctica. The detail is much influenced by terrain to create textures that override climate, which might suggests that the results flatter to deceive. Yet the modelling does result in valleys and broad basins of unconsolidated sediment showing shallower depths that tallies with the tendency for less infiltration where slopes are steep and run-off faster. The fact that the degree of fit between model and known hydrogeology is high does suggest that at the regional scale the maps are very useful points of departure for more detailed work that brings in lithological and structural information.

Hug a Hydrogeologist: It’s National Groundwater Awareness Week, 10-16 March! (aquadoc.typepad.com)
30 Facts About The Coming Water Crisis That Will Change The Lives Of Every Person On The Planet (landandlivestock.wordpress.com)

Pushing back the origin of photosynthesis

Published on February 27, 2013 by zooks7771 Comment

More than a decade ago the oldest sedimentary rocks in the world at Isua in West Greenland hit the headlines, and not for the first time. Inclusions of graphite in crystals of the mineral apatite from the Isua supracrustals had yielded carbon isotopes unusually deficient in ¹³C relative to ¹²C, which is often regarded as a sign that life was involved in the carbon cycle at the time. The Isua rocks have been reliably dated at around 3.8 billion years (Ga) so that added over 400 Ma to the time at which life was present on Earth. Sedimentary rocks formed at 3.4 Ga contain the first tangible signs in the form of stromatolites thought to have been secreted by biofilms of blue-green bacteria which are oxygen-generating photosynthesisers. Sadly, limestones at Isua, indeed all the putative sedimentary rocks there were metamorphosed and deformed plastically so that such features, if they were ever present, had been obliterated. Apatite was thought to be so strong and resistant to heating that carbon within its crystals would have preserved original isotopic ‘signatures’. Detailed studies to test this hypothesis refuted the early age for life, which reverted back to around 3.4 Ga. But Isua presents too good an opportunity for its geochemical secrets to be left uninvestigated.

The latest targets are its iron isotopes. Isua includes metamorphosed banded ironstones composed largely of magnetite and quartz. Magnetite is iron oxide (Fe₃O₄) and begs the question of how such an oxygen-rich mineral formed in such volumes in sediment if photosynthesizing life had not made elemental oxygen available. That would oxidize soluble ferrous ions (Fe²⁺) to the insoluble ferric form (Fe³⁺) in order for iron oxide to precipitate from sea water in large amounts. There is no other means known for oxygen to be produced in a planet’s surface environment. A team at the University of Wisconsin’s NASA Astrobiology Institute, led by Andrew Czaja and joined by Stephen Moorbath of the University of Oxford, who set the entire West Greenland story rolling by leading its geochronological investigation since the early 1970s, have made a breakthrough (Czaja, A.D. et al. 2013. Biological Fe oxidation controlled deposition of banded iron formation in the ca. 3770 Ma Isua Supracrustal Belt (West Greenland). Earth and Planetary Science Letters, v. 363, p. 192-203).

Any element that has more than one naturally occurring isotope offers the possibility of studying various kinds of chemical process by looking for changes to the relative proportions of the different isotopes. Having different relative atomic masses isotopes of an element have slightly different chemical properties so that one is likely to be more favoured in a reaction than another. In the case of iron, the most important reactions in surface processes are those that depend on reducing and oxidising conditions, i.e. producing soluble Fe²⁺ and insoluble Fe³⁺ respectively. Oxidation and precipitation of iron oxides and hydroxides tend to favour the heavier isotope ⁵⁶Fe over the more common ⁵⁴Fe resulting in an increase in the ⁵⁶Fe/⁵⁴Fe ratio (δ⁵⁶Fe). This is found throughout the Isua ironstones, but may again reflect metamorphism. However, such was the detail of this study that δ⁵⁶Fe values were measured for many individual bands. Instead of showing roughly the same values throughout the rock, each band had a different value. That strongly suggests that values produced during sedimentation had been preserved. It seems that a bacterial mechanism of oxidation was involved. Moreover, by comparing the 3.8 Ga Isua ironstones with examples dated at 2.5 Ga from Australia the team found different isotopic values that implicates different kinds of bacteria involved in producing apparently similar rock types. The twist is that the most likely bacterial type involved at Isua may have been a photosynthesiser, but not of the kind that releases elemental oxygen instead transferring it from water to combine directly with the ions of iron that its photosynthesis had oxidised. The younger ironstones seem more likely to have involved cyanobacteria that do excrete oxygen; shortly after their formation the Earth’s surface increasingly became oxygen-bearing.

Throughout the Precambrian, BIFs appear and then vanish from the record only to reappear when geologist least expect them, for instance around the time of the Snowball Earth events in the Neoproterozoic Era. Iron isotopes could well become handy tools to probe the processes that formed them.

Rusty rocks reveal ancient origin of photosynthesis (newscientist.com)

K-T (K-Pg) event: can the havering stop now, please?

Published on February 19, 2013 by zooks7772 Comments

Since 1980, when Alvarez père et fils discovered signs of a globe-affecting impact event in rocks marking the stratigraphic boundary at the end of the Mesozoic Era –between the Cretaceous and Palaeogene Periods – there has been continual bickering over the cause of the mass extinction at that time. Unlike other mass extinctions that one marked the end of an Era dominated in the popular mind by the iconic dinosaurs. Besides that focus, many geologists have been averse to external, ‘wham-bam-thank-you-ma’am’ explanations for shifts in the fossil record: a sort of Lyellian view that geological change had to be at the pace of the humble tortoise and must be due to something in the Earth system itself. Then a majority, this conservative faction looked instead to the effects of the voluminous basalt flood that had affected western India at around the same time. Incidentally, that apparent match to the end-Mesozoic extinction sparked an interest in volcanic associations with other mass extinctions.

Discovery by geophysicists of evidence for a large almost completely buried impact basin, about 180 km across, centred in the Caribbean off Mexico’s Yucatan Peninsula swayed opinion towards an extraterrestrial cause when it became clear that the impact had occurred around the time of the K-Pg boundary, then placed at 65 Ma. Soon there were claims that the Deccan Traps had erupted in less than a million years at that time, together with doubts cast on the actual age of the Chicxulub crater. The time-spread of the Deccan volcanism enlarged with more dating to between 68 and 60 Ma; and so the to-ing and fro-ing continued, gleaning sizeable grants for entrepreneurial geoscientists keen on one or other of what were becoming bandwagon topics. Then the ‘golden spike’ marking the time of the mass extinction became the subject of controversy. A means of precise dating is to examine signs in sediments of cyclical climate change using the Milankovich approach, although before 50 Ma only the 405 ka cyclicity predicted from astronomy is readily detected. Using well-dated volcanic horizons to calibrate such a stratigraphic dating method might be the key, but it became apparent that 65.3, 65.7 or 66.1 Ma all seemed to have the same likelihood.

The two kill mechanisms that had been proposed are in fact very different, not merely in terms of what might have happened to atmospheric chemistry, climate, photosynthesis and so on, but concerning their timing. Repeated episodes of major basalt eruption every 100 ka or so would have had a chronic and perhaps cumulative effect on the Earth’s biota; i.e. even a 10 Ma spread for Deccan basalt floods bracketing the actual die-off would be acceptable as a cause. An impact however takes no more than a second to occur, because of the hypersonic speed induced by Earth’s gravity as well as that of the asteroid through the Solar System. All its immediate effects – entry flash; crater excavation; debris fall-out; atmospheric dust and toxic gas accumulation; climate change; acid rain and tsunamis – would have been done and dusted over a matter of a few thousand years. The Chicxulub impact would have been a catastrophe that was instantaneous in geological terms. Its occurrence would need to bear the same date as the mass extinction itself to be seen as incontrovertible; well, at least to the majority of geoscientists. That point seems to have been reached.

As well as the crater, Chicxulub scattered molten rock far and wide to appear in the ‘boundary layer’ as glass spherules, which are dateable using radiometric means. So too is the timing of the mass extinction itself, provided suitable materials can be found above and below the strata across which fossil abundances change so dramatically. Paul Renne of the University of California, Riverside, and colleagues from the US, the Netherlands and Britain dated impact glasses from Haiti and volcanic ash from the late Cretaceous to early Palaeogene terrestrial sediments of Montana, USA that bracket the extinction event using multiple argon-isotope studies and the ⁴⁰Ar-³⁹Ar method (Renne, p.r. and 8 others 2013. Time scales of critical events around the Cretaceous-Paleogene boundary. Science, v. 339, p.684-687. The glasses come out at 66.038+0.049 Ma, while the Ar-Ar age of volcanic ash just above the carbon-isotope anomaly that marks the world-wide disappearance of a large proportion of living biomass is 66.019+0.021 Ma. As they say, the ages are ‘within error’ and the error is very small indeed.

So, does this work mark the end of the K-Pg controversy? Probably not, as very large sums of grant money are still tied up with on-going studies. Perhaps to assuage the fears of all those still financially addicted to answering ‘what killed the dinosaurs?’, The abstract of the paper reads thus’ ‘The Chicxulub impact likely triggered a state shift of ecosystems already under near-critical stress’.

Artist's impression of the common ancestor of placental mammals (Credit: Science magazine) — Artist’s impression of the common ancestor of placental mammals (Credit: Science magazine)

Interestingly, in the very same issue of Science came a research article that reexamines taxonomy of 86 key living and fossil placental mammals in the light of genetic sequencing, to locate startigraphically their earliest common ancestor (O’Leary, M.A. and 22 others 2013. The placental mammal ancestor and the post-K-Pg radiation of placentals. Science, v. 339, p. 662-667). That seems to wrap up, for now, another controversy; did diminutive placental mammals arise unnoticed beneath the gaze of mighty dinosaurs, or what? It seems that some precursor mammals were able to diversify and produce a line whose fetuses grow and are nourished in the mothers uterus attached to a placenta, before live birth at an advanced stage of development, once opportunities for diversification emerged after the K-Pg event. Morphologically, the ancestor of everything from a naked mole rat to a blue whale and, of course, ourselves, seems to have been a sneaky-looking little beast with a long nose and pointy teeth. It does look like it, or its predecessor, could have scuttled unscathed amongst the leaf litter as dinosaurs engaged in their death prance…

Rebuilding Our Extinct Ancestor (ribosometranslation.wordpress.com)
What Killed Dinosaurs: New Ideas About the Wipeout (news.nationalgeographic.com)

Update on a classic British field site

Published on February 8, 2013 by zooks7773 Comments

Few expect Earth scientists to get all sentimental, but they do. My soft spot is for one of the most rewarding and least strenuous geological sites in Britain, Norber Brow near Austwick on the southern edge of the Yorkshire Dales National Park. As well as the famous glacial erratics of Silurian greywackes perched on Lower Carboniferous limestone, 250 m to the SE by a well-trodden path is the inverse, the Variscan unconformity at the base of the Carboniferous on the very same Silurian formation. I was lucky to be taken there at age 15 by Roy Happs who taught A-level Geology, and it decided my future, there and then.

The erratics don’t just site on the limestone, but are on pedestals up to 30 cm above the surrounding limestone surface as if carefully balanced by Beowulf’s assailant Grendel. Somehow, since the time glacial flow had deposited the Silurian boulders the underlying limestone had been dissolved away; but how fast was that? That is the key to the pace at which limestone pavement, to most general visitors such a stunning and unexpected feature of the Dales, might have formed. And such a delight to hear of its terminology: clints, redolent of the former Viking people of the Dales, that stand proud between deep fissures known as grikes, a suitably ominous term of unknown derivation. Such superbly fractal landforms are, of course, but one part of karst (from the eponymous region of limestone country in Slovenia).

It is really satisfying to discover that a lot of cutting-edge science has recently been aimed at Norber from a substantial review in Earth Pages’ sister journal Geology Today (Wilson, P. et al. 2013. Dating in the Craven Dales. Geology Today, v. 29 (January-February Issue), p. 16-22). The length of time that the Norber erratics have been exposed to cosmic-ray bombardment has been determined from ¹⁰Be, ²⁶Al and ³⁶Cl analyses with a precision of ±1000 years to 17.9 ka, shortly after the last glacial maximum (LGM) when warming and glacial melting had just begun in this part of Yorkshire. That might seem to indicate an average of 330 mm of limestone had been dissolved over that period to form the pedestals, i.e. a dissolution rate averaging about 20 micrometres per year, which is extremely rapid, geologically speaking. In 1962 when I was show the site we were told that elsewhere the limestone pavement had formed since the first field systems (Iron Age) were laid out as now useless drystone walls crossed it. Roy Happs somewhat darkly suggested that they had formed since the start of the Industrial Revolution because of acid rain.

He was pretty much wrong on that score, but cosmogenic dating of the clints shows significant discrepancies between the age of deposition of the erratics and and the exposure age of the clints. This suggests both chemical dissolution and also periods of frost shattering and gravel removal, perhaps by soil creep. Dating of other materials enlivens the history of local landform development. Another karstic feature is the presence of sinkholes or dolines that are often filled with yellowish silts that show clear textural evidence of being windblown sediments or loess. These aeolian sediments have long been regarded as post-LGM too, but optically stimulated luminescence dating of their quartz grains gives an age split between pre- (27.5 ± 2.6 ka) and post-LGM (16.5 ± 1.7 ka). Some loess elsewhere in Craven district comes out to be as young as 8.2 ka, to tally with evidence from Greenlandic ice cores for a sudden deterioration in North Atlantic seaboard climate during this early time in the Holocene.

Then there are the local caves, renowned in Victorian times for their cave bears and other mammal fossils. One bear skull from Victoria Cave in the Craven area gave a ¹⁴C age of 14.6 ± 0.4 ka which statistically coincides with that from a cut-marked horse vertebra. More than likely the bears were turfed out when humans reached Craven, but did they return when humans fled in the face of the Younger Dryas return to frigid-desert conditions? Probably not, as the YD would almost have sterilized what are now the Yorkshire Dales. Even earlier ages of 114 ka from U-Th dating of calcite flowstone that embeds hippo, elephant, rhino and hyena bones in Victoria Cave date to the previous Eemian interglacial. Indeed this speleothem has yielded ages as far back as the limit of the U-Th method (%00 ka). On a solo expedition in 1964 I had the chance to sleep-over in Victoria Cave, but pressed on with goose bumps to the nearby Youth Hostel.

Geology and creationism

Published on February 6, 2013 by zooks7774 Comments

Creationism is a topic about which I would not normally comment for much the same reason that once prompted pub landlords to have a sign behind the bar reading ‘No politics, no religion’. Yet geology has played an historically central role in the debate about Genesis vs Science. An excellent summary of how this emerged and was fundamentally resolved in favour of scientific endeavour, even if the ‘Genesisists’ have not been entirely rooted out, appeared in the Geological Society of America’s GSA Today in November 2012 (Montgomery, D.R. 2012. The evolution of creationism. GSA Today, v. 22, p. 4-9).

Starting with Steno’s break with a literal acceptance of Genesis in 1669, the dominant view grew among clerics as well as scientists – ‘back in the day’ often one and the same – that the Earth was far older and its history one of changing natural processes. That outlook prevailed to strengthen through the late-18^th and 19^th centuries. Of course there was a tendency among ‘people of the Book’ somehow to blend their religious and scientific views, along the line that ‘scientific revelations that contradicted biblical interpretations provided natural guidance for better interpreting scripture’. But by the end of the 19^th century there were very few literal creationists though a great many Christians who endorsed attempts to reconcile biblical text and geology. Yet long after the Reverend William Buckland finally admitted in the mid-19^th century that his imagination had ruled his zealous quest for evidence of a Noachian Flood and abandoned a literal idea of that and other aspects of Genesis there remained a persistent dribble of creationism.

A wry view of Young-Earth Creationism (Photo credit: seriouscher)

That minor current split in the 20^th century into a ‘tanky’ tendency that defended young-Earth creation and a global flood in the last ten thousand years, and a more ‘moderate’ wing of ‘old-Earth’ creationists. ‘Old-Earthers’ happily accept geological evidence of great antiquity, but maintain that God made it for eventual use by humanity; i.e. it had just sat around awaiting Adam and Eve being expelled from Eden. Both wings evolved along equally bizarre paths using a logic that boils down to a blend of perversity and simply ignoring any contrary evidence, such as that unearthed by Buckland long before. For instance when confronted by the fact that the deepest parts of the oceans contain less sediment than has accumulated on the continents, they defy gravity by insisting that ocean basins were eroded out by the Flood and then deposited with all their internal structures intact on higher ground.

Unsurprisingly, most creationists believe that there has been a centuries-long conspiracy by scientists to mislead the rest of humanity. Were it not for the fact that more than 40% of people in the United States believe in young-Earth creation, David Montgomery’s account of what is now a somewhat one-sided yet stupidly lively debate as regards true evidence would be amusing. His concluding sentence, ‘How many creationists today know that modern creationism arose from abandoning faith that the study of nature would reveal God’s grand design for the world?’ is probably one of the best ways of enraging any creationist who tries to enlighten you: he/she will certainly not just go away, but in the foam they generate you should be able to make good your escape.

Creationism vs. Evolution: Ground-Breaking Discovery by Physics Engineer Solves Vital Facet of Origins Debate. (prweb.com)
NO! Christians do NOT believe the Earth is 5,000 years old! (mbtimetraveler.com)

Related articles

Share this:

Share this:

Share this:

Related articles

Share this:

Related articles

Share this:

Related articles

Share this:

Share this:

Related articles

Share this:

Related articles

Share this:

Related articles

Share this:

Related articles

Share this:

Related articles

Share this:

Related articles

Share this:

Share this:

Share this:

Share this:

Related articles

Share this:

Share this:

Share this:

Share this:

Related articles

Share this:

Related articles

Share this:

Related articles

Share this:

Share this:

Related articles

Share this: