> Conley has a response to this argument. Even if a microbe on Mars shares the same deep origins as us, a few thousand years down a separate evolutionary pathway would still make them pretty alien indeed. But ultimately, the best case for caution, and for planetary protection, may be simply to point to all the ways in which our knowledge of Mars has changed just in the past few years. Curiosity ended up almost on top of possible liquid water because we didn’t know what we didn’t know. In a way, Conley’s deepest arguments boil down to a quote from Haldane: “The universe is not only queerer than we suppose, but queerer than we can suppose.”