[meteorite-list] Mass Extinction Comes Every 62 Million Years, UC Physicists Discover

From: Lars Pedersen <lbp_at_meteoritecentral.com>
Date: Mon Mar 21 13:24:55 2005
Message-ID: <000601c5259a$964e1ca0$b300a8c0_at_acerteimgf71uk>

Looks like we are next.... was?nt it 65 Million years ago last time ?

;-)
Lars

----- Original Message -----
From: "Ron Baalke" <baalke_at_zagami.jpl.nasa.gov>
To: "Meteorite Mailing List" <meteorite-list_at_meteoritecentral.com>
Sent: Thursday, March 10, 2005 6:41 PM
Subject: [meteorite-list] Mass Extinction Comes Every 62 Million Years,UC
Physicists Discover


>
>
> http://sfgate.com/cgi-bin/article.cgi?f=/c/a/2005/03/10/MNGFIBN6PO1.DTL
>
> Mass extinction comes every 62 million years, UC physicists discover
> David Perlman,
> San Francisco Chronicle
> March 10, 2005
>
> With surprising and mysterious regularity, life on Earth has flourished
> and vanished in cycles of mass extinction every 62 million years, say
> two UC Berkeley scientists who discovered the pattern after a
> painstaking computer study of fossil records going back for more than
> 500 million years.
>
> Their findings are certain to generate a renewed burst of speculation
> among scientists who study the history and evolution of life. Each
> period of abundant life and each mass extinction has itself covered at
> least a few million years -- and the trend of biodiversity has been
> rising steadily ever since the last mass extinction, when dinosaurs and
> millions of other life forms went extinct about 65 million years ago.
>
> The Berkeley researchers are physicists, not biologists or geologists or
> paleontologists, but they have analyzed the most exhaustive compendium
> of fossil records that exists -- data that cover the first and last
> known appearances of no fewer than 36,380 separate marine genera,
> including millions of species that once thrived in the world's seas,
> later virtually disappeared, and in many cases returned.
>
> Richard Muller and his graduate student, Robert Rohde, are publishing a
> report on their exhaustive study in the journal Nature today, and in
> interviews this week, the two men said they have been working on the
> surprising evidence for about four years.
>
> "We've tried everything we can think of to find an explanation for these
> weird cycles of biodiversity and extinction," Muller said, "and so far,
> we've failed."
>
> But the cycles are so clear that the evidence "simply jumps out of the
> data," said James Kirchner, a professor of earth and planetary sciences
> on the Berkeley campus who was not involved in the research but who has
> written a commentary on the report that is also appearing in Nature today.
>
> "Their discovery is exciting, it's unexpected and it's unexplained,"
> Kirchner said. And it is certain, he added, to send other scientists in
> many disciplines seeking explanations for the strange cycles. "Everyone
> and his brother will be proposing an explanation -- and eventually, at
> least one or two will turn out to be right while all the others will be
> wrong."
>
> Muller and Rohde conceded that they have puzzled through every
> conceivable phenomenon in nature in search of an explanation: "We've had
> to think about solar system dynamics, about the causes of comet showers,
> about how the galaxy works, and how volcanoes work, but nothing explains
> what we've discovered," Muller said.
>
> The evidence of strange extinction cycles that first drew Rohde's
> attention emerged from an elaborate computer database he developed from
> the largest compendium of fossil data ever created. It was a 560-page
> list of marine organisms developed 14 years ago by the late J. John
> Sepkoski Jr., a famed paleobiologist at the University of Chicago who
> died at the age of 50 nearly five years ago.
>
> Sepkoski himself had suggested that marine life appeared to have its ups
> and downs in cycles every 26 million years, but to Rohde and Muller, the
> longer cycle is strikingly more evident, although they have also seen
> the suggestion of even longer cycles that seem to recur every 140
> million years.
>
> Sepkoski's fossil record of marine life extends back for 540 million
> years to the time of the great "Cambrian Explosion," when almost all the
> ancestral forms of multicellular life emerged, and Muller and Rohde
> built on it for their computer version.
>
> Muller has long been known as an unconventional and imaginative
> physicist on the Berkeley campus and at the Lawrence Berkeley
> Laboratory. It was he, for example, who suggested more than 20 years ago
> that an undiscovered faraway dwarf star -- which he named "Nemesis" --
> was orbiting the sun and might have steered a huge asteroid into the
> collision with Earth that drove the dinosaurs to extinction.
>
> "I've given up on Nemesis," Muller said this week, "but then I thought
> there might be two stars somewhere out there, but I've given them both
> up now."
>
> He and Rohde have considered many other possible causes for the 62-
> million-year cycles, they said.
>
> Perhaps, they suggested, there's an unknown "Planet X" somewhere far out
> beyond the solar system that's disturbing the comets in the distant
> region called the Oort Cloud -- where they exist by the millions -- to
> the point that they shower the Earth and cause extinctions in regular
> cycles. Daniel Whitmire and John Matese of the University of Louisiana
> at Lafayette proposed that idea as a cause of major comet showers in
> 1985, but no one except UFO believers has ever discovered a sign of it.
>
> Or perhaps there's some kind of "natural timetable" deep inside the
> Earth that triggers cycles of massive volcanism, Rohde has thought.
> There's even a bit of evidence: A huge slab of volcanic basalt known as
> the Deccan Traps in India has been dated to 65 million years ago -- just
> when the dinosaurs died, he noted. And the similar basaltic Siberian
> Traps were formed by volcanism about 250 million years ago, at the end
> of the Permian period, when the greatest of all mass extinctions drove
> more than 70 percent of all the world's marine life to death, Rohde said.
>
> The two scientists proposed more far-out ideas in their report in
> Nature, but only to indicate the possibilities they considered.
>
> Muller's favorite explanation, he said informally, is that the solar
> system passes through an exceptionally massive arm of our own spiral
> Milky Way galaxy every 62 million years, and that that increase in
> galactic gravity might set off a hugely destructive comet shower that
> would drive cycles of mass extinction on Earth.
>
> Rohde, however, prefers periodic surges of volcanism on Earth as the
> least implausible explanation for the cycles, he said -- although it's
> only a tentative one, he conceded.
>
> Said Muller: "We're getting frustrated and we need help. All I can say
> is that we're confident the cycles exist, and I cannot come up with any
> possible explanation that won't turn out to be fascinating. There's
> something going on in the fossil record, and we just don't know what it
> is."
>
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Received on Thu 10 Mar 2005 12:57:11 PM PST