(2011) by Ted Nield, Granta, hrdbk, £20.00, 271pp, ISBN 978-1-847-08241-1
Ted Nield is a doctor of geology and editor of Geoscientist (the news magazine of the Geological Society).. Written from that perspective, his book is an excellent introduction to meteoritics (the science of meteorites and impacts) as well as to the ongoing dynamic processes which shape the Earth. In his account of how humanity has reacted to impact events during recorded history, other reviewers have perhaps made too much of the incident where a meteorite briefly became the chief god of ancient Rome, but it is a high spot in a generally good read. One recurring point is the sheer unwillingness of the emerging natural sciences community to recognise that such events occurred, regardless of the evidence, until they were witnessed by scientists in person and could no longer be ignored.
Coming to modern times, Ted Nield gives us the evolution of the idea that asteroids and comets could have caused mass extinctions in the past, and still pose a global threat today. One point he does not make, but freely acknowledged on his recent visit to Glasgow, is that in the early 1960s the idea that impacts could cause such harm was so controversial that some of the earliest papers were published by science fiction magazines. In a painting for Willy Ley's The Conquest of Space (1949), the artist Chesley Bonestell imagined an event on the scale of the Barringer Meteorite crater occurring on Manhattan Island. Bad as it looked, streets were still recognisable. Bridges were still standing, though some were broken, and ships could be seen at some of the piers. When Isaac Asimov realised that destruction on that scale could be caused by a much smaller nickel-iron meteorite weighing a few dozen tons, the size of a large desk, perhaps it was natural for him to publish in his regular column for Fantasy & Science Fiction. ('The Rocks of Damocle', reprinted in Asimov on Astronomy, Macdonald & Jane’s, 1974). But when other writers went on to consider the destructive effects of impactors a mile in diameter, they pretty well had to publish in the monthly science feature of Analog because more reputable outlets would have none of it. (Ralph A. Hall, ('Secondary Meteorites', Analog, January 1964; J.E. Enever, 'Giant Meteor Impact', Analog, March 1966.)
Having picked up on those articles at the time, and having highlighted the issues in my own New Worlds for Old (David & Charles, 1979), I remember the feeling of relief later that year when the BBC’s lunchtime radio news ran an item on the suggestion, by Walter and Luis Alvarez, that the discovery of a thin layer of iridium, at the Cretaceous-Tertiary (K-T) geological boundary, indicated a giant impact coinciding with and probably causing the extinction of the dinosaurs – now associated with the Chicxulub crater off Yucutan. Respectability at last! But having followed and reviewed the issues in detail, Ted Nield now takes a different view. Scientists who say the Chicxulub impact did not kill the dinosaurs are now finding it hard to get a hearing, by their own account, and while Nield points out that nevertheless their views are known, he feels a degree of sympathy. In his view, attributing the extinction of the dinosaurs and other lifeforms at that time to a single cause is too simplistic, and at odds with what is known about other such events. He believes it has a great deal more to do with the near-simultaneous but prolonged and complex effects of the volcanic plume which formed the Deccan Traps in India. The K-T impact may have contributed, may even have provided the coup de grace, but it was not the major cause.
One major reason for his scepticism is that no other mass extinctions have been correlated with impacts. To that I would reply that there are known impact events which have still to be dated, particularly a very large crater under the Antarctic ice which was discovered by the Soviets in the 1960s. (F.Yu. Zigel, The Minor Planets, NASA TT F-700, US Govt. Printing Office, 1972.) Of the various books attempting to describe the destructiveness of the K-T impact, the most lurid is The Great Extinction by Michael Allaby and James Lovelock (Secker & Warburg, 1983). But the horrors they describe are largely overkill when Enever's 'Giant Meteor Impact' (Analog, March 1966) provides enough damage to create mass extinctions every time something that size hits the sea.
So we might argue that the Chicxulub impact could have caused the mass extinction on its own, even if as it happens, it did not. Here the biggest revelation of the book comes from Sweden, where geological conditions have preserved the record of a sustained bombardment of the Earth, lasting up to 15 million years but with a peak of one to two million years, during the Ordovician Period (488-444 million years ago). The falling bodies stemmed from the ‘Gefion family’, a group of asteroids which were formed when a body 100-150 km in diameter was shattered by a collision, roughly 485 million years ago. Supporting evidence in the form of micrometeorites is now turning up all over the world, along with craters formed by larger bodies, and statistically it is to be expected that at least one of those events would be of the size of the Chicxulub impact. Yet far from being associated with a Great Dying, the Ordovician period represents one of the most prolific phases in the evolution of life on Earth(1). (There was a mass extinction at the end of the Ordovician, but that was probably due to climate change as the Gondwana supercontinent drifted across the South Pole.)
From all of that, Dr. Nield concludes that impacts or even bombardments are not the threat to life on Earth that has been supposed. I would not go that far: it strikes me, for instance, that if there was only one Ordovician impact in the Chicxulub range, but it happened on land, things could have been very different had it fallen at sea. But even if he is right, his subtitle takes a very long view of what is good for life on Earth and what is not: I was reminded of Dougal Dixon’s After Man, A Zoology of the Future (Granada, 1981), which imagined that we take ourselves out and most of the higher species with us, but after 50 million years all the evolutionary niches (except ours) have filled up again, so that is all right. In running a project to consider options for deflecting or mitigating asteroid threats, I have been surprised, not to say distressed, by the number of people who believe or claim to be believe that we should do nothing, letting nature take its course with us.
Incoming! mentions proposals to deflect impactors only twice, and then only to say that the Bruce Willis scenario with nuclear weapons is probably a bad idea, which it is. But while Ted Nield was in Glasgow, Astronomers of the Future invited him to give us a talk and put the question, 'What would you want done if we knew there was going to be an impact?'. Dr. Nield conceded that if he had to share in its consequences, if it happened, he would just as soon that some efforts were made to prevent it.
Incoming is an enjoyable read with entertaining personal perspectives, and I would recommend it as a historical introduction to meteoritics. Although I don’t feel that the case for the subtitle has been made, this book is an interesting counterpart to the near-unanimity of the books about impacts on my ‘asteroids and comets’ shelf. No doubt it will arouse further discussions and debate which will help to stimulate interest in the topic, and in view of its importance, that can only be good.
Duncan Lunan
A version of this review has appeared in Cosmic Aspects No.1, the online magazine of Astronomers of the Future [www.astronomersofthefuture.net].
(1) Editor's note: The Ordovician followed the Cambrian and its boom with the rise of plants and animals, so the Earth's biosphere was seeing new ecological niches, not to mention co-evolutionary opportunities from the new trophic levels (new rungs on the food chain ladder) that animals and plants created. Also there was a minor extinction event at the end of the Cambrian which provided 'empty' ecological niches in the Ordovician. Hence the Ordovician was a period that saw considerable evolution.
See also elsewhere on this site a review of Ted Nield's Supercontinent: Ten Billion Years of Life on our Planet.
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