Washington: If the scientists are to be believed, the earth is on the brink of its sixth mass extinction. The intensity of the earth is very low as compared to the past five catastrophes.

"If you look only at the critically endangered mammals, it clearly tells us that we are moving into the mass extinction realm," said lead author Anthony Barnosky, a UC professor of integrative biology.

"If currently threatened species actually extinct and that rate of extinction continued, the sixth mass extinction could arrive within as little as 3 to 22 centuries," he said.

Professor Barnosky, who is also a curator at the Museum of Paleontology in Berkeley, said that it's not too late to save these critically endangered mammals.

That would require dealing with a perfect storm of threats, including habitat fragmentation, invasive species, disease and global warming, the paleobiologist warned.

For the research, Prof Barnosky and his team estimated the range of plausible rates for the mass extinctions from the fossil record and then compared those rates to present status.

Biologists estimate that within the past 500 million years, at least 80 mammal species have gone extinct.

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.