Mankind may have unleashed the sixth known mass extinction in Earth’s history, according to a paper released on Wednesday by the science journal Nature. The study concludes that Earth's creatures are on the brink of a sixth mass extinction, comparable to the one that wiped out the dinosaurs and it calculates that three-quarters of today's animal species could vanish within 300 years.
Species naturally come and go over long periods of time. But what sets a mass extinction apart is that three-quarters of all species vanish quickly. Earth has already endured five such events over the past 540 million years including the one that wiped out dinosaurs and many other creatures 65 million years ago. Conservationists have warned for years that the world is in the midst of a sixth, human-caused extinction, with species from frogs to birds to tigers threatened by climate change, disease, loss of habitat and competition for resources with nonnative species.
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.
Palaeo-biologists 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.
The baiji dolphin is functionally extinct, orangutans are disappearing and even some species of bats—the most numerous of mammals—are dying out.
"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 is really gloom-and-doom stuff," continues Barnosky of the University of California, Berkeley. "But the good news is we haven't come so far down the road that it's inevitable."
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.
The most abrupt extinction came at the end of the Cretaceous, some 65 million years ago when a comet or asteroid slammed into the Yucatan peninsula, in modern-day Mexico, causing firestorms whose dust cooled the planet.
An estimated 76 percent of species were killed, including the dinosaurs.
The authors admitted to weaknesses in the study. They acknowledged that the fossil record is far from complete, that mammals provide an imperfect benchmark of Earth’s biodiversity and further work is needed to confirm their suspicions.
But they described their estimates as conservative and warned a large-scale extinction would have an impact on a timescale beyond human imagining.
lost "a few (percent) of species, nothing like the 75% we lost in the past, so we still have a lot more out there to save," says Barnosky, who glumly adds, "Walk outside, look around and imagine three-fourths of all the different kinds of life you see gone. Ask yourself if you'd be happy living in that world."
"So far, only one to two percent of all species have gone 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 biotic to save," Barnosky said.
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."
The silver lining in this dark cloud is that if humans work quickly to protect endangered and threatened species and their habitats now, the mass extinction can be prevented or at least delayed by thousands of years, says Barnosky.
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