Scientists try to determine if life on Earth is quickly heading toward extinction

Neil Jones neil at
Thu Mar 3 00:22:46 EST 2011

  Scientists try to determine if life on Earth is quickly heading toward

By NADIA DRAKE - San Jose Mercury News
SAN JOSE, Calif. Life on Earth is hurtling toward extinction levels 
comparable to those following the dinosaur-erasing asteroid impact of 65 
million years ago, propelled forward by human activities, according to 
scientists from the University of California, Berkeley.

This week, scientists announced that if current extinction rates 
continue unabated, and vulnerable species disappear, Earth could lose 
three-quarters of its species as soon as three centuries from now.

"That's a geological eyeblink," said Nicholas Matzke, a graduate student 
at UC Berkeley and author of a paper describing the doom-and-gloom 
scenario. "Once you lose species, you don't get them back. It takes 
millions of years to rebound from a mass extinction event."

This means that not too far in the future, back yards might not be 
buzzing with bees, bombarded by seagulls or shaded by redwood trees. And 
while that might seem far off, species already are disappearing on a 
global scale. In recent history, we've lost the dodo bird and the 
passenger pigeon, the Javan tiger and the Japanese sea lion, and now, 
maybe the eastern cougar - declared extinct by the U.S. Fish and 
Wildlife Service on Wednesday. Amphibians, mammals, plants, fish - none 
are immune to going the way of the dinosaurs, courtesy of the human 
impact on fragile ecosystems.

Such enormous losses have only occurred five times in the past 
half-billion years, during events known as "mass extinctions." The 
best-known of these events occurred 65 million years ago - a "really bad 
day," according to paleontologists - when an asteroid collided with 
Earth, sending fiery dust into the atmosphere and rapidly cooling the 
planet. These "Big Five" events set the extinction bar high: to reach 
mass-wipeout status, 75 percent of all species need to disappear within 
a geologically short time frame, meaning that Earth is currently on the 
brink of the sixth mass extinction.

To determine whether current losses could equal these mass extinction 
rates, scientists compared recent rates with species die-offs during the 
Big Five, taking into account presently endangered species. They also 
looked at the number of species lost in recent history, and found that 
while rates are dramatically higher than expected, the percentage of 
vanishing species is not elevated - yet. We already are engaged in a 
seemingly inexorable march toward barren landscapes and empty seas, a 
procession fueled by human population growth, resource consumption and 
climate change, according to scientists.

"The good news is, we still have most of what we want to save," said 
Berkeley paleobiologist and lead study author Anthony Barnosky. "But 
things are clearly going extinct too fast today."

The paper, published in this week's issue of Nature, resulted from a 
graduate seminar Barnosky organized in fall 2009. Together, he and 
students used fossils to compare extinction rates with more modern data, 
wanting to answer whether we really are seeing the sixth mass 
extinction. To make comparisons, scientists used information from 
well-preserved fossils and modern accounts of disappearing animals, 
focusing on our milk-bearing relatives: mammals.

Stanford University biologist Paul Ehrlich, who was not involved in the 
study, said evidence of the sixth extinction is all around. For years, 
he studied the Bay Checkerspot butterfly on Stanford's campus - but 
then, the butterfly disappeared from the campus, more than a decade ago.

And, when Ehrlich journeyed to Morocco to sample a different Checkerspot 
species, he found no butterflies, just "sheep droppings and not one 
blade of grass."

"Anywhere you go around the world," Ehrlich said, "If you're a field 
biologist, your sites and organisms are disappearing."

One particularly vulnerable group is marine mammals, according to study 
author and paleobiologist Charles Marshall, who said that while 
predictions are dire for our swimming relatives, they haven't yet 
reached the point of no return. "There really is time to reverse habitat 
destruction or massive overexploitation of resources," Marshall said. "I 
love sushi, but I just don't eat tuna anymore. I don't want to be part 
of the decline of that group."

Scientists say habitat destruction, global climate change, introducing 
invasive species, and population growth are contributing to losses.

"Those four things working in concert are kind of a perfect storm that's 
setting up a recipe for disaster," Barnosky said. "But people are the 
ones who are driving this extinction, so we can fix it."

In addition to prioritizing species preservation, Ehrlich suggested 
starting with caps on human population growth and limiting resource 
consumption. "We could do something about it, but I don't see that we 
have the slightest inclination to," he said.

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