The Earth could be on the brink of the sixth mass extinction in history, claim scientists.

They believe that the steep decline in populations of many animal species, from frogs and fish to tigers, is as fast as any of the last five extinctions in the past 540 million years.
In a study, to be published in the journal Nature, University of California scientists assess where mammals and other species stand today in terms of possible extinction, compared with the past 540 million years.
""If you look only at the critically endangered mammals – those where the risk of extinction is at least 50 percent 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,"" said Professor Anthony Barnosky.
""If currently threatened species – those officially classed as critically endangered, endangered and vulnerable – actually went extinct, and that rate of extinction continued, the sixth mass extinction could arrive within as little as 3 to 22 centuries,"" he said.
Nevertheless, Prof Barnosky said it was not too late to save these critically endangered mammals and other such species and stop short of the tipping point.
That would require dealing with a perfect storm of threats, including habitat fragmentation, invasive species, disease and global warming,
""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,"" he said. ""We still have a lot of Earth's biota to save.""
Biologists estimate that within the past 500 years, at least 80 mammal species have gone extinct out of a starting total of 5,570 species. The team's estimate for the average extinction rate for mammals is less than two extinctions every million years, far lower than the current extinction rate for mammals.
""It looks like modern extinction rates resemble mass extinction rates, even after setting a high bar for defining 'mass extinction,'"" Prof Barnosky said.
(Source: Daily Telegraph)