  It is sometimes assumed that the rapidity of biogenesis on Earth suggests
that life is common in the Universe. Here we critically examine the assumptions
inherent in this if-life-evolved-rapidly-life-must-be-common argument. We use
the observational constraints on the rapidity of biogenesis on Earth to infer
the probability of biogenesis on terrestrial planets with the same unknown
probability of biogenesis as the Earth. We find that on such planets, older
than ~ 1 Gyr, the probability of biogenesis is > 13% at the 95% confidence
level. This quantifies an important term in the Drake Equation but does not
necessarily mean that life is common in the Universe.
