World's sixth mass extinction may be underway: study

by Richard Ingham and Laurent Banguet

PARIS (AFP) – Mankind may have unleashed the sixth known mass extinction in Earth's history, according to a paper released by the science journal Nature.

Over the past 540 million years, five mega-wipeouts of species have occurred through naturally-induced events.

But the new threat is man-made, inflicted by habitation loss, over-hunting, over-fishing, the spread of germs and viruses and introduced species, and by climate change caused by fossil-fuel greenhouse gases, says the study.

Evidence from fossils suggests that in the "Big Five" extinctions, at least 75 percent of all animal species were destroyed.

Palaeobiologists at the University of California at Berkeley looked at the state of biodiversity today, using the world's mammal species as a barometer.

Until mankind's big expansion some 500 years ago, mammal extinctions were very rare: on average, just two species died out every million years.

But in the last five centuries, at least 80 out of 5,570 mammal species have bitten the dust, providing a clear warning of the peril to biodiversity.

"It looks like modern extinction rates resemble mass extinction rates, even after setting a high bar for defining 'mass extinction," said researcher Anthony Barnosky.

This picture is supported by the outlook for mammals in the "critically endangered" and "currently threatened" categories of the Red List of biodiversity compiled by the International Union for Conservation of Nature (IUCN).

On the assumption that these species are wiped out and biodiversity loss continues unchecked, "the sixth mass extinction could arrive within as little as three to 22 centuries," said Barnosky.

Compared with nearly all the previous extinctions this would be fast-track.
Four of the "Big Five" events unfolded on scales estimated at hundreds of thousands to millions of years, inflicted in the main by naturally-caused global warming or cooling.

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