What Would It Take to Completely Sterilize the Earth?

The odds of finding life on another planet hinge on the answers to two big questions. First, how often does life arise? Second, once it does arise, how likely is it to persist without being completely wiped out? The first question is extremely difficult, especially since we have exactly one example of a life-spawning planet. But the second question is easier to answer—at least for Earth—and a trio of astrophysicists have given it a shot.

In a paper delightfully titled “,” and , both from the University of Oxford, and , from Harvard University, estimated the odds that a space-borne catastrophe like an incoming asteroid would completely sterilize the Earth. Reassuringly, they think those odds are astronomically low—about one in 10 million for every billion years. “The conclusion we come to is that life, once it starts