Is Earth due for a mass extinction?

Scientists writing in the journal ‘Nature’ warn that we could be on the brink of a mass extinction,the kind of species loss that has happened just five times in the last 540 million years.

“If you look only at the critically endangered mammals–those where the risk of extinction is at least 50 per cent within three of their generations–and assume that their time will run out and they will be extinct in 1,000 years,that puts us clearly outside any range of normal and tells us that we are moving into the mass extinction realm,” Anthony Barnosky,an integrative biologist at the University of California at Berkeley said in a statement about the study he co-wrote.

Are humans to blame? Possibly.

“A modern global mass extinction is a largely unaddressed hazard of climate change and human activities,” said H. Richard Lane of the National Science Foundation,which funded the research.

If the species that are now considered critically endangered,endangered and vulnerable actually went extinct,and that rate of extinction continued,the sixth mass extinction could arrive in three to 22 centuries,Barnosky said.

This is by no means a sure thing,and the scientists said there is still time to save endangered species short of a tipping point. That would require dealing with a perfect storm of threats,including habitat fragmentation,invasive species,disease and global warming.

The last mass extinction was 65 million years ago when a space rock slammed into what is now the Yucatan peninsula,one of several factors that caused the big die-off. Previous events occurred 200 million years ago,251 million years ago,359 million years ago and 443 million years ago.

Polar bears are sometimes seen as symbols of endangered species,and in the United States they are listed as threatened under the Endangered Species Act because their icy habitat is melting away. The most recent animal to be designated as extinct by US authorities is the eastern cougar.