March 4, 2011

Latest Global Extinction Underway?

Paleobiologists at the University of California at Berkeley are studying the state of biodiversity today, using the world's mammal species as a barometer. Mammal extinctions were very rare: on average, just two species died out every million years, until humans' largest expansion yet, some 500 years ago.

In the last five centuries however, at least 80 out of 5,570 mammal species have disappeared, thinning out the biodiversity of the planet. "It looks like modern extinction rates resemble mass extinction rates, even after setting a high bar for defining "Ëœmass extinction," researcher Anthony Barnosky tells AFP.

This would be the sixth mass extinction in Earth's history, according to a paper released by the science journal Nature. Five mega-wipeouts of species have occurred through naturally-induced events over the past 540 million years.

This new threat, however, is man-made. Habitation loss, germs and viruses spreading quicker than ever, over-hunting, over-fishing and introduced species are all major causes of species die-off, along with climate change caused by fossil-fuel greenhouse gases, says the study. Fossils evidence suggests that in the previous 5 mass extinctions, at least 75 percent of all animal species were destroyed.

Four of these 5 events played out on time scales estimated at hundreds of thousands to millions of years, primarily by naturally-caused global warming or cooling. The Cretaceous period, some 65 million years ago came to a sudden end when a comet or asteroid slammed into the Yucatan peninsula causing fire storms whose dust cooled the planet. An estimated 76 percent of species were killed, including the dinosaurs which opened the door to the growth of modern mammal species.

Admitting to weaknesses in the study, researchers acknowledged that the fossil record is far from complete and that mammals provide an incomplete benchmark of Earth's biodiversity, but they described their estimates as conservative and explain that a large-scale extinction would have an impact beyond human imagining.

"Recovery of biodiversity will not occur on any time frame meaningful to people," said the study. "Evolution of new species typically takes at least hundreds of thousands of years, and recovery from mass extinction episodes probably occurs on time scales encompassing millions of years," Barnosky continued.

Not all is hopeless, Barnosky tells AFP, "So far, only one to two percent of all species have gone extinct in the groups we can look at clearly, so by those numbers, it looks like we are not far down the road to extinction. We still have a lot of Earth's biota to save."

Even so, "it's very important to devote resources and legislation toward species conservation if we don't want to be the species whose activity caused a mass extinction."

French biologist Gilles Boeuf, president of the Museum of Natural History in Paris, when asked for an independent observation, said the question of a new extinction was first raised in 2002. So far, scientists have identified 1.9 million species, and between 16,000 and 18,000 new ones, essentially microscopic, are documented each year.

"At this rate, it will take us a thousand years to record all of Earth's biodiversity, which is probably between 15 and 30 million species" said Boeuf. "But at the rate things are going, by the end of this century, we may well have wiped out half of them, especially in tropical forests and coral reefs."


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