Abstract

I forgive the slight spin of sloganeering conveyed by the motto so frequently cited by proponents of a cosmos chock full of organisms: "Life will fed a way." Life is resilient and quite capable (especially in bacterial form) of living in the most damnably improbable places-from nearly boiling ponds in Yellowstone National Park to tiny pores in rocks as deep as two miles below the earth's surface. But even this degree of resilience must work within limits; if life ever evolved on the Martian surface during its initial billion years with running water, the planet's later desiccation probably extinguished our solar system's second experiment in advanced carbon chemistry.