Shock and Er … wait a minute

Enhanced gravity map of the Chicxulub crater (credit: Wikipedia)

Michael Rampino has produced a new book (Rampino, M.R. 2017. Cataclysms: A New Geology for the Twenty-First Century. Columbia University Press; New York). As the title subtly hints, Rampino is interested in mass extinctions and impacts; indeed quite a lot more, as he lays out a hypothesis that major terrestrial upheavals may stem from gravitational changes during the Solar System’s progress around the Milky Way galaxy. Astronomers reckon that this 250 Ma orbit involves wobbling through the galactic plane and possibly varying distributions of mass – stars, gas, dust and maybe dark matter – in a 33 Ma cycle. Changing gravitational forces affecting the Solar System may possibly fling small objects such as comets and asteroids towards the Earth on a regular basis. In the 1980s and 90s Rampino and others linked mass extinctions, flood-basalt outpourings and cratering events, with a 27 Ma periodicity. So the books isn’t entirely new, though it reads pretty well.

Such ideas have been around for decades, but it all kicked off in 1980 when Luis and Walter Alvarez and co-workers published their findings of iridium anomalies  at the K-Pg boundary and suggested that this could only have arisen from a major asteroid impact. Since it coincided with the mass extinction of dinosaurs and much else besides at the end of the Cretaceous it could hardly be ignored. Indeed their chance discovery launched quite a bandwagon. The iridium-rich layer also included glass spherules, shocked mineral grains, soot and other carbon molecules –nano-scale diamonds, nanotubes and fullerenes whose structure is akin to a geodesic dome – and other geochemical anomalies. Because the Chicxulub crater off the Yucatán Peninsula of Mexico is exactly the right age and big enough to warrant a role in the K-Pg extinction, these lines of evidence have been widely adopted as the forensic smoking gun for other impacts. In the last 37 years every extinction event horizon has been scrutinized to seek such an extraterrestrial connection, with some success, except for exactly coincident big craters.

The K-Pg event is the only one that shows a clear temporal connection with a small mountain falling out of the sky, most of the others seeming to link with flood basalt events and their roughly cyclical frequency – but hence Rampino’s Shiva hypothesis that impacts may have caused the launch of mantle plumes from the core-mantle boundary. Others have used the ‘smoking gun’ components to link lesser events to a cosmic cause, the most notorious being the 2007 connection to the extinction of the North American Pleistocene megafauna and the start of the Younger Dryas return of glacial conditions. Since 1980 alternative mechanisms for producing most of the impact-connected materials have been demonstrated. It emerged in 2011 that nano-diamonds and fullerenes may form in a candle flame and their global distribution could be due to forest fires. And now it seems that shocked mineral grains can form during a lightning strike (Chen, J. et al. 2017. Generation of shock lamellae and melting in rocks by lightning-induced shock waves and electrical heating. Geophysical Research Letters, v. 44, p. 8757-8768; doi:10.1002/2017GL073843). Shocked or not, quartz and feldspar grains are resistant enough to be redistributed into sediments. Although platinum-group metals, such as iridium, are likely to be mainly locked away in Earth’s core, some volcanic exhalations and many flood basalts – especially those with high titanium contents – significantly are enriched in them. So even the Alvarez’s evidence for a K-Pg impact has an alternative explanation. Rampino is to be credited for acknowledging that in his book.

An awful lot of ideas about rare yet dreadful events in the biosphere depend, like many criminal cases, on the ‘weight of evidence’ and defy absolute proof. The evidence generally permits alternatives, such the cunning Verneshot hypothesis for the extinction-flood basalt connection supported by one of the founders of plate tectonics, W. Jason Morgan. As regards The K-Pg extinction, it is certain that a very large mass did fall on Chicxulub at the time of the mass extinction, whereas the Deccan flood basalts span a million years or so either side. But the jury is out on whether either or both did the deed. For other events of this scale and larger ones the money is on internal origins. As for Rampino’s galactic hypothesis, the statistics are decidedly dodgy, but chasing down more forensics is definitely on the cards.

Animation showing the Chicxulub Crater impact. ( credit: University of Arizona, Space Imagery Center)

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Stepping Stones eBook

A revised and updated edition of Stepping Stones: The Making of Our Home World by Steve Drury, first published in 1999, has been released as a free eBook on the book’s web site https://earthstep.wordpress.com/. The revision incorporates the hundreds of commentaries on geoscientific advances written since 2000 by Steve for earth-pages. It is a personal view of the evolution of the Earth System and the emergence of humanity from it. First published by Oxford University Press, Stepping Stones was widely acclaimed by  fellow Earth scientists and general readers.

Some old habits die hard

Earth Pages News does not usually contain book reviews, but two that I read over the Christmas break deserve a comment.  The first, The Lunar Men: The Friends Who Made The Future (Jenny Uglow, Faber & Faber, 2002) shows how what is now becoming known as the geosciences was central to the wide-ranging discourses and research of that group of men who created the foundations of modern science in Britain.  The Lunar Society was a loose association of free-thinking individuals, which included Matthew Boulton, Erasmus Darwin, James Watt, James Priestley, Josiah Wedgwood and James Hutton, who became close friends and collaborators at the dawn of the Industrial Revolution.  All emerged from the religious nonconformism that lay outside the aristocratic establishment of the late 18^th century, but each came from different backgrounds.  What united them was an all-consuming curiosity as well as a desire to make a living.  Each was driven in his own way to serve those less fortunate, as well as to take their own wealth and talents to whatever limits they had.  Not one was a specialist, and they shared all their interests, ideas and discoveries, as well as supporting one another intellectually, economically and socially.  These were not men in thrall to peer-review or the building of academic empires.  Collectively they challenged established views of all kinds, and took the greatest delight in doing so, even when subject to physical attack, as was Priestley.

The characters depicted in The Dinosaur Hunters (Deborah Cadbury, Fourth Estate, 2001) are from one or two generations later, and do not cut such a merry dash.  Central figures are Gideon Mantell, William Buckland and Richard Owen.  They worked in a period when the challenge of the Lunar Society had created a state defence of religious orthodoxy (almost a panic), and in which a new and partitioned scientific establishment had emerged.  The first dinosaur remains were discovered by the daughter of a carpenter, subsisting on Poor Relief, who supplemented her family’s subsistence by selling Jurassic fossils that she had become adept at finding on the beaches of Lyme Regis.  170 years before the advent of the Open University, Mary’s brilliant insights brought no academic benefits to her, but many to the Reverend geologists who plagiarised her in exchange for just enough cash to keep her and her family in bread and potatoes.  The central characters, however, are Gideon Mantell and Richard Owen.  Mantell, a rural doctor, became obsessed with ancient reptiles following his and his wife’s discoveries of fragments of the Iguanodon.  He felt driven to make his name in scientific circles from outside the establishment, and a tough time he had, despite his growing insight and assiduous collection.  Owen, who hardly collected a specimen in his entire career, relied on his anatomical skills to describe, classify and steal those of others, such as Mantell.  The founder of the Natural History Museum (with Prince Albert’s patronage), Owen clawed his way to the pinnacle of British science over the backs of those more honest and naïve than himself.  Although he was exposed as a plagiarist and scoundrel by Thomas Huxley, Charles Darwin’s “bulldog”, following the publication of On The Origin of Species, Owen’s main victim Mantell had already died a broken man.  William Buckland, by all accounts a genuinely nice man, ended his days in a lunatic asylum having tried to square the growth of material evidence for evolution with his own deep religious beliefs.

Having read both books in quick succession, it was difficult to avoid the conclusion that the best spirit of the “Lunar Men” seems largely to have departed from our science, while the meanest spirit of Victorian times lingers on among self-promoting empire builders with ever-narrower specialisations.