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Joined: Nov 2000
Posts: 866
old hand
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old hand
Joined: Nov 2000
Posts: 866 |
Timely Q wwh....
A geological bookshop near me just closed down and was getting rid of everything at ridiculous prices - including $0!
Among other titles (including The SAS Survival Handbook!!), I got two copies of "Evolutionary Catastrophes - The Science of Mass Extinction" (Vincent Courtillot - trans. by Joe McClinton, Cambridge University Press, 1999) It's a slim volume and a relatively easy read, strongly geological, but followable - pay the postage and you're welcome to the 2nd copy!
M. Courtillot gives fair treatment to all the prevailing hypotheses on the subject. Basically there's two schools - those who promote cosmic impacts and those who prefer a terrestrial source - including Courtillot - and now stales. He believes vulcanism the likes of which has not been seen in modern times was a more frequent offender than impacts. To quote:
"....every 20 or 30 Ma (million years) or so, an immense bubble of material from the mantle becomes unstable, rises to the surface and bursts. Its emergence triggers gigantic explosive eruptions and finally lays down millions of cubic kilometres of basalt within a few tens or hundreds of thousands of years. Some ten (sites) have been identified from the past 300Ma. Seven of them coincide with seven mass extinctions, and in particular with the two largest ones (including the Cretaceous/Cenozoic ("KT") boundary often attributed to the Chicxulub impact).........Eruptions of such magnitude seem able to affect the biosphere by injecting ash, aerosols, and gases - and they can probably cause darkness, temperature variations and acid rain. It is clear that rarely, but sharply, the internal dynamics of the globe affect the evolution of species.......No doubt it's hard for human beings to imagine the end of the species they belong to, or to concieve that over 99.9% of the species that ever lived on Earth are already extinct. (My emphasis).
Courtillot cites evidence that the Chicxulub impact occured during one of the episodes of vulcanism. He concludes that it may have contributed to the unhappy state of the planet but that it was not the causitive event.
His book is a brave attempt to reconcile the schools of thought. Since the 1980 article about Chicxulub in Science there have been 2,000 papers published on the subject!!
stales
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Joined: Jan 2001
Posts: 13,858
Carpal Tunnel
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OP
Carpal Tunnel
Joined: Jan 2001
Posts: 13,858 |
Dear stales: In the past year there have been quite a few papers about possible role of methane hydrate in the KT catastrophe. I saw a paper describing massive sediment slump off Norway 8,000 years ago that must have sent a huge tsunami towards British Isles. And I have seen a couple papers saying deposits off North Carolina could slump, and tsunami could devastate large part of east coast US.
But if I remember right, the presence of iridium at KT boundary cannot be attributed to volcanism.
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Joined: Aug 2001
Posts: 2,605
Carpal Tunnel
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Carpal Tunnel
Joined: Aug 2001
Posts: 2,605 |
pay the postage and you're welcome to the 2nd copy!
stales, if dr. bill passes on that offer, I call dibs -- PM me please!
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Joined: Nov 2000
Posts: 866
old hand
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old hand
Joined: Nov 2000
Posts: 866 |
wwh - Correct again - the presence of that much iridium is a sure indicator of asteroid impact. As mentioned in the previous post however, the impact was during an event of tumultuous vulcanism. The Ir rich layer occurs in the midst of a huge thickness of basalt flows, indicating it was not the cause of the vulcanism. Courtillot postulates that the material released into the atmosphere during the volcanic event exceeded that of the impact.
stales
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