Scientists try to determine if life on Earth is quickly heading toward extinction
neil at nwjones.demon.co.uk
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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