[NMScience] The Mystery of Mass Extinctions Is No Longer Murky

[Ellen Loehman]

>From NSF: 
http://www.nsf.gov/news/news_summ.jsp?cntn_id=111722&govDel=USNSF_51

If you are curious about Earth's periodic mass extinction events such as the
sudden demise of the dinosaurs 65 million years ago, you might consider
crashing asteroids and sky-darkening super volcanoes as culprits.

But a new study, published June 15, 2008, in the journal Nature, suggests
that it is the ocean, and in particular the epic ebbs and flows of sea level
and sediment over the course of geologic time, that is the primary cause of
the world's periodic mass extinctions over the past 500 million years.

"The expansions and contractions of those environments have pretty profound
effects on life on Earth," says Shanan Peters, a University of
Wisconsin-Madison assistant professor of geology and geophysics and the
author of the new Nature report. In short, according to Peters, changes in
ocean environments related to sea level exert a driving influence on rates
of extinction, which animals and plants survive or vanish, and generally
determine the composition of life in the oceans.

Since the advent of life on Earth 3.5 billion years ago, scientists think
there may have been as many as 23 mass extinction events, many involving
simple forms of life such as single-celled microorganisms. Over the past 540
million years, there have been five well-documented mass extinctions,
primarily of marine plants and animals, with as many as 75-95 percent of
species lost. For the most part, scientists have been unable to pin down the
causes of such dramatic events. In the case of the demise of the dinosaurs,
scientists have a smoking gun, an impact crater that suggests dinosaurs were
wiped out as the result of a large asteroid crashing into the planet. But
the causes of other mass extinction events have been murky, at best.

"No matter what the ultimate driving extinction mechanisms might be at any
one time, Professor Peters brings the repeated and resultant extinction on
oceanic shelves front and forward where it belongs," says National Science
Foundation (NSF) Program Manager Rich Lane. "This breakthrough speaks loudly
to the future impending modern shelf extinction due to climate change on
Earth."

... More in actual report


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Ellen Loehman
loehman at aps.edu