Tuesday, May 18, 2004

And the lord said...Boom!....................

I hadn't discussed this when the news came out, but I wanted to bring it up, because some reading this may be interested...

Evidence for a Large Impact at the Permian-Triassic Boundary

Article Posted: May 14, 2004
By: David Morrison

A newly discovered impact crater near Australia might be implicated in the greatest mass extinction of all time, 251 million years ago.


A NASA news conference was held May 13 to announce the discovery of an impact crater near Australia that might be implicated in the greatest mass extinction of all time the Permian-Triassic or PT event, 251 million years ago.

Identification of the cause of this critical event for the history of life on our planet is one of the major challenges of paleontologists and astrobiologists. As Michael Benton recently wrote (Michael J. Benton: "When Life Nearly Died  The Greatest Mass Extinction of All Time," Thames & Hudson, 2003):

"The end-Permian mass extinction may be less well known than the end-Cretaceous, but it was by far the biggest mass extinction of all time. Perhaps as few as 10 percent of species survived the end of the Permian, whereas 50 percent survived the end of the Cretaceous. Fifty percent extinction was associated with devastating environmental upheaval. But there is an enormous difference between 50 percent survival though the end-Cretaceous and only 10 percent survival through the end-Permian. The key difference & is in the diversity of founders available for the reflowering of life after the catastrophe. The survival of only 10 percent of species means that many major groups of plants, animals, and microbes have probably gone forever."

As was mentioned in the discussion during the NASA news conference, at the time when early paleontologists first recognized the PT boundary, some suggested that all life had been killed on Earth, and that the Creator started over with entirely new life forms.

The new research is by geochemist and oceanographer Luann Becker (Dept. of Geology, Univ. of California, Santa Barbara), and her colleagues R. J. Poreda, A. R. Basu, K. O. Pope, T. M. Harrison, C. Nicholson, and R. Iasky. The paper title is "Bedout: A Possible End-Permian Impact Crater Offshore Northwestern Australia". The paper abstract is reproduced below.

The paper reports on the identification of a large submarine impact structure off western Australia that is dated at 250.7 +/- 4.3 million years (an argon-argon date from a single plagioclase crystal). This geological rise had previously been thought to be volcanic, but a re-examination of drill cores by this team shows clear evidence of impact materials, including abundant shocked mineral grains. Their preliminary work suggests that this original crater was nearly as large as the Chicxulub crater, which caused the KT extinction 65 million years ago.

Recent work by others has shown that the extinction at the end of the Permian was extremely rapid, like that at the end of the Cretaceous. Less is known generally, however, about the earlier extinction. Some other evidence of an impact at the PT boundary has been found, but so far no significant iridium anomalies such as those that first suggested an impact at the KT boundary.

The interpretation of these great mass extinctions is complicated. Both the KT and the PT event have been associated with large volcanic eruptions, although the time scale for volcanism is millions of years, not the thousands of years (or less) that account for the great dying. Few scientists today think the Deccan volcanism 65 million years ago played a major role in the KT extinction, but many have proposed that the even larger Siberian eruptions of 250 million years ago might have been responsible for the PT extinction. In the case of the KT, there was a great deal of early evidence of an extraterrestrial event, but the discovery of the actual crater was key to wide acceptance of the reality of the impact catastrophe 65 million years ago. Identification of a large crater with age 251 million years might also resolve the PT debate, but a great deal more work needs to be done.

Doug Irwin of the National Museum of Natural History, Smithsonian Intuition, who also participated in the NASA press conference, stated that the arguments that this might be the PT impact crater are interesting but not compelling. He noted that while the evidence for an impact at the PT has been growing over the past couple of years, he would still not be able to say that an impact was more likely than a volcanic explanation, or perhaps some other cause. The PT event remains one of the big mysteries of the history of life on Earth.


Obviously there is still much work to be done to prove or disprove the impact hypothesis, but it appears quite possible that what is known as the "the Great Dying" 250 million years ago, when 90 percent of marine and 80 percent of land life perished in a very short time, was caused by a piece of space rock crashing in to our planet.

It must have been one big piece of space rock too, because the crater they are talking about connecting to the PT extinction is 125 MILES across....

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