Re:Permo-Triassic extinction

[Jeff Hecht <jhecht@world.std.com>]

Charles Johnson wrote:
>
>Dr. David King of Auburn University claims that a 300 km crater caused by
>an impactor striking Gondwanaland is associated with the P-Tr extinction.
>This compares with the 200 km Chicxulub crater.
>
>An example of his claim can be found at his rather introductory-level
>chapter on the K-T extinction at http://www.auburn.edu/~kingdat/chap2.htm
>
That's the first I've heard of this claim, and I've been following this
story for a few years. When I checked the web site, I found he thinks that
the Falklands/Malvinas are part of the crater. This hasn't gotten any
serious scientific scrutiny, and probably wouldn't survive much. There have
been claims of shocked quartz from the Permo-Triassic, but serious searches
have found no iridium anomaly, another impact signature, and the shocked
quartz is at best from only two sites, in Australia and New Zealand.

In short, I'd urge considerable caution. It's easy to weave impact
theories; it's hard to demonstrate their validity.

What are the implications for dinosaur extinction? Having spent some time
studying the big mass extinctions, I have come to believe each has its own
distinct set of causes, and we're not got to find any one single cause.
It's clear that an impact happened at the K-T, the biggest impact in at
least a couple hundred million years, and it coincides with the biggest
extinction in that period. But the factors don't seem to be the same as at
the Permo-Triassic, when a large part of the oceans became anoxic.

-- Jeff Hecht