Some conservationists have been using the term "the sixth extinction" for a few years now—referring to the possibility that more than 75% of existing species could disappear for the sixth time in the planet's history—but there's been little factual proof to back up the frightening prediction. Until now. A new paper warns that if no changes are made, we might indeed be at the beginning of the sixth mass extinction to strike the Earth. If the rate of extinction, which is currently accelerating, continues unabated—and if all the animals currently listed as "critically endangered" do go extinct—then a mass extinction could transpire within as little as three centuries or as long as 2,200 years, cautions the paper published in the journal Nature.
All previous mass extinctions have also taken many centuries to transpire, USA Today reports. Researchers say their calculations are based on fairly conservative estimates, but also acknowledge that more study is needed. And there is hope, since the threat is still at an early stage: So far the Earth has only 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 the lead author—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." (And animals may not be the only thing we could run out of...)