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Approximately 65 million years ago, when the dinosaurs went extinct, 75% of the planet's many species went with them. It was the world's fifth, and most recent, mass extinction event.

Now, according to a July 25 review in the journal Science, the Earth seems to be at the cusp of a sixth mass extinction. Only this time, an asteroid is not to blame. We are.

"Human impacts on animal biodiversity are an under-recognized form of global environmental change," the team of ecologists and biologists warn in Science. "Among terrestrial vertebrates, 322 species have become extinct since 1500, and populations of the remaining species show 25% average decline in abundance."

A third of all vertebrates, the scientists write, "are threatened or endangered."

There are several long-time drivers of what researchers call "defaunation" — the decline of various animal species. The study points to " overexploitation, habitat destruction, and impacts from invasive species" as continuing threats, but notes that soon, human-caused climate change will be the number one driver of defaunation. Diseases that come from pathogens introduced by humans are another growing threat.

The good news? We're not yet totally doomed.

As David Biello writes in Scientific American:

To avoid the sixth mass extinction we will probably have to employ more aggressive conservation, such as moving species to help them cope with a changing climate . Think re-wilding: reintroducing species like wolves or beavers that were once present in a given ecosystem but have since disappeared. Aggressive conservation might also mean killing off newcomer species to preserve or make room for local flora and fauna.

As another study in Science notes, we've already made headway in saving some animals from what seemed like certain ruin.

But if humans as a species don't want to take our chances with a sixth mass extinction, we need to start taking drastic measures now. The momentum is already moving against us.





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