Did life emerge spontaneously on earth, or did it come from outer space
10 The scientific community is sharply split on the question, and the evidence from Mars (火星) not only heats up the debate but also adds a third possibility: life-forms may have arisen on Mars first and then hitched a ride on a meteorite (陨石) to Earth—or vice versa.
As Stanford University chemist Richard Zare puts it, "Who is to say that we are not all Martians"
Sounds implausible Consider the alternatives. Sir Fred Hoyle, the distinguished British astronomer, favors an even more radical theory. The idea is that billions of years ago, the solar system was peppered by biological "seeds", which took root wherever conditions were right. That would explain how life may have arisen at roughly the same time on Earth and on Mars.
11 But it also raises awkward questions about where those seeds came from and what, or who, sent them flying through space.
There is something to this theory.
12 Even scientists who reject it acknowledge that some of life"s building blocks probably had extraterrestrial (外星的) origins.
Indeed, they now believe that everything from organic chemicals to amino acids (氨基酸), the constituents of proteins, was carried in by the comets, asteroids (小行星) and meteorites.