February 2013 – Earth-logs

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)

The production of geoscientists: a cautionary tale from the Open University

Published on February 4, 2013 by zooks7772 Comments

Despite global recession, worldwide job opportunities for geoscientists are increasing faster than the number of available applicants. In the US the Bureau of Labor Statistics predicts 21% growth in this sector in 2010-2020 (Perkins, S. 2011. Geosciences: Earth works. Nature, v. 473, p. 243–244). That figure does not include jobs freed-up by retirement: the demographics of employed geoscientists in the petroleum and mining industries are skewed markedly to the over-40s, peaking at age 50.

The American Geological Institute’s Geoscience Workforce Program has reported that the regions that produce most geoscience graduates, the US, Europe, Russia and China, are not meeting their domestic needs let alone global requirements. The demand stems from the traditional petroleum and mineral industries that are booming, together with the renewable energy sector and growing concern about environmental hazards and impacts attending global warming.

An editorial (Rare Earth scientists) in the December 2012 issue of Nature Geoscience is headlined, ‘Not enough young people enter the geosciences. A passion for the subject should be sparked early on.’ It then comments that the decline in young people studying the geosciences at school stems from Earth science not being taken seriously, under-education of their teachers and budgetary sacrifice of geoscience to preserve the more ‘traditional’ science subjects. The leading article concludes, ‘On an increasingly vulnerable planet, governments need to teach the young people of their country an understanding of the Earth’s basic make-up and dynamics, along with inspiring a fascination for its age and beauty. How else can we expect humanity to survive the Anthropocene?’

For over 40 years the Open University has been a key UK educator in geoscience. Since 1971 a total of about 170 thousand, mainly British students have studied at home through the OU for a science-based degree. Discovering tectonics, Earth structure, geology and palaeontology through studying the Science Foundation Course must have been a thrilling experience because since 1972, when the OU began to offer a level-2 course in Geology, around 30 thousand of its science ‘beginners’ decided to find out more; an average enrolment of 760 per year. The OU’s Department of Earth Sciences added more level-2 courses so that by 2000, students could also study economic geology (The Earth’s Physical Resources – 18 500 students from 1974 to 2009, averaging 544 per year), planetary science (The Earth: Structure, Composition and Evolution- 14 100 students from 1981 to 2005, averaging 590 per year) and Earth-system science (Earth and Life –7121 students from 1997 to 2006, averaging 712 per year).

After 1981 Open University students could, and many did, aim for a geoscience-oriented degree that also took in three, more advanced, level-3 studies. These were Oceanography (12 121 students from 1989 to 2012, averaging 505 per year), stratigraphy (The Geological Record of Environmental Change – 7968 students from 1976 to 2012, averaging 295 per year) and Earth’s internal processes (Understanding the Continents – 6994 students from 1976 to 2012, averaging 259 per year).

In this way the Open University became one of the world’s largest single providers of geoscience education, if not the largest: in the whole of the United States fewer than 3000 first degrees majoring in geoscience are awarded annually. Yet from its inception the OU’s Department of Earth Sciences had never claimed to be training professional geologists: had it been, its graduates would have significantly affected the world’s employment opportunities in the discipline. In fact that claim could never have been made, for one simple reason: distance learning for part-time students would always struggle to provide the volume of hands-on practical training that is the quintessence of this pre-eminently field- and lab-based discipline. Nevertheless the OU’s range of residential schools where practical activities were intensively provided for went a good way towards filling this gap.

So, to those unfamiliar with the realities of the OU milieu it will seem odd that in 2012 the world’s largest provider of distance learning axed all residential courses right across the science spectrum, including those in practical geoscience. But to those directly involved this move was the logical final step in a series of changes since 2001. Before that, for those courses that included a residential component attendance had been compulsory, except in special circumstances. Yet after 2001 university authorities deemed that the residential schools continue only as optional components for degree study and should carry an additional registration fee. Not surprisingly, in the case of the core level-2 Geology course attendance at the re-branded residential school declined to 30% after 2001.

Two other important developments attended this change in the Earth Science degree programme. After 2001 pass rates fell abruptly. For example, in the Science Foundation Course the rate fell from an annual average of 69 to 54%, and in level-2 Geology from 65 to 55%. Because residential schools played a vital role in boosting confidence and reinforcing home studies, equally as important as transferring practical skills, this dramatic fall in performance was only too predictable.

The other post-2001 development was an across-the-board fall in new registrants for Earth Science level-2 courses, especially in those that had previously not been served by residential studies: The Earth: Structure, Composition and Evolution from a pre-2001 average of 680 per year to 470 thereafter; Earth and Life from 866 to 558; The Earth’s Physical Resources from 795 to 456. The majority of those who enrolled for these courses having previously studied the core Geology course such dramatic declines are easily explained. Those who had opted out of the residential course missed its undoubted boost to confidence and enthusiasm, and reinforcement in basic geoscientific principles. More likely to underperform in the Geology course, they would not have felt equipped to deal with other level-2 courses, and ‘voted with their feet’.

Since its launch, The Earth’s Physical Resources course had been acclaimed by geoscience teachers internationally for having made economic geology fascinating rather than a chore. In 2005-7 it had been completely refurbished and rising registrations bucked the downward trend. Yet in 2009, it was axed with little discussion. Declining enrolment for The Earth and Earth and Life prompted management to withdraw both and combine parts of their content in a single course Our Dynamic Planet: Earth and Life. Launched in 2007, by 2012 it attracted a mere 217 applicants. In 2013 it too will be withdrawn from the curriculum.

In late 2010 the OU’s Department of Earth Sciences held a celebration of its 40-year existence; yet only a year later in 2011 the department that had brought plate tectonics, advanced palaeontology, unravelling past climates, physical resources; planetary science and much besides to the widest student audience ever achieved ceased to be. It was merged into a restructured entity called the Department of Environment, Earth and Ecosystems. There seems to have been a failure of nerve and leadership that may have important consequences not only for the future of geoscience as a discipline and among the wider public but for the very knowledge necessary for our national and human survival. The future availability of remaining geoscience courses is uncertain, with all being expected to start for the last time within the next year or two. Perhaps some major transformation to meet increased needs for general public awareness of the way our planet works is being planned: let’s hope so and that any new offerings have as much impact as the earlier courses did before the start of the 21^st century. It will be a hard task, as the Open University tripled its fees for students entering the OU system from 2012 onwards.

NOTE: (added 11 February 2013) The Open University has been offered the right of reply to this item.

Open University under threat by Nick Rogers in The Geoscientist November 2012 issue
Geology is Going Digital and Getting Way More Fun (onlinecollege.org)
Cindy Yeilding Shows Us How STEM Careers Rock (forbes.com)

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