[Vision2020] Precarious Situation?

[Ted Moffett]

Meteors not only culprit in mass extinction
Scientist say volcanoes, climate change threatened many species
*By Michael Schirber*
LiveScience

Updated: 3:12 p.m. PT Oct 27, 2006

Apocalypses may not be all fire and brimstone.

A growing number of paleontologists say that Earth-smashing meteors cannot
take all the blame for the many mass extinctions that dot our planet's
fossil record. The true causes seem to be more complex.

"The [meteor] impact model has been so successful because it's easy to
explain and easy to understand," said Nan Arens of Hobart and William Smith
College in Geneva, NY. "However, the simple answer isn't always the best
one."

At the annual meeting of the Geological Society of America this week in
Philadelphia, Arens and others argued that the combined punch of volcanoes,
climate change and impacts leaves many species teetering on the brink of
extinction <http://www.livescience.com/animalworld/060718_big_animals.html>.
One final blow brings collapse.

The same scenario could be happening now.

*Dino disappearance
*The most famous of all giant space rocks is the one that presumably killed
off the non-avian dinosaurs 65 million years ago, in the so-called K-T
extinction event<http://www.livescience.com/animalworld/060831_KT_biodiversity.html>.
But this may not be the whole story.

For several years, Gerta Keller of Princeton University and her colleagues
have been arguing that the widely-accepted dino-killer — a space rock that
left a 100-mile-wide crater around Chicxulub, Mexico — happened 300,000
years too soon. Keller therefore believes that this impact was just one of
several smoking guns.

"Impacts by themselves simply don't cause major mass extinctions," Keller
told LiveScience.

Keller advocates a scenario in which the Chicxulub meteor combined with
volcanoes in India and global warming to unsettle the ecologic balance. She
has compiled data prior to K-T event that show many species shrinking in
size — a sign of an unhealthy environment.

Keller speculates that a second, currently unidentified meteor crashed after
Chicxulub. This impact, in conjunction with a surge in volcanism, "dealt the
final blow to a Cretaceous biota already on the brink of extinction," Keller
said.

*Great Dying
*A similar environmental deterioration may have preceded the biggest retreat
in life's history.

The P-T extinction event, or Great
Dying<http://www.livescience.com/animalworld/050414_mass_extinction.html>,
occurred 251 million years ago when up to 90 percent of all species were
snuffed out. David Bottjer's group from the University of Southern
California has studied the fossil record and found clear signs that species
were in peril long before they disappeared.

The reason: "The Earth got sick," Bottjer said.

The illness began when Siberian volcanoes triggered global warming, he
explained. This reduced ocean circulation and the oxygen
supply<http://www.livescience.com/animalworld/050414_mass_extinction.html>.
These hazardous conditions were a boon for sulfur-eating microbes, which
released toxic hydrogen sulfide into the atmosphere, finishing off most of
the life that remained.

*Common diagnosis
*A sick Earth succumbing to a final shock is apparently a common extinction
formula. Arens and her colleagues analyzed geologic data from the last 488
million years and found more species died out when the environment was first
stressed and then stung.

Specifically, the researchers compared stress-inducing volcanic activity and
catastrophic meteor impacts. Only when the Earth experienced both did
extinction rates significantly increase.

"Periods of stress are going to reduce population sizes," Arens said. With
reduced numbers, "species are vulnerable to pulse catastrophes."

On the flip side, an unstressed environment is resilient to geologic and
climatic disasters because life is diverse and geographically spread out.

Applying their model to the present, Arens and her collaborators speculate
that human activity has both stressed the environment with agriculture and
shocked it with fossil fuel burning.

Whether or not this is an accurate description, both Bottjer and Keller
agree that we are in a precarious
situation<http://www.livescience.com/environment/060320_diversity.html>
.

"Under [current] conditions any disaster that might strike (impact or
volcanism or major greenhouse warming), which ordinarily would not cause
major extinctions, will put much of Earth's biota at risk of extinction,"
Keller said.
*(c) 2006 LiveScience.com. All rights reserved. *
URL: http://www.msnbc.msn.com/id/15446092/

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Vision2020 Post: Ted Moffett
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