Panspermia

Panspermia (or exogenesis) is the hypothesis that life on Earth originated from somewhere else in space, and that alien organisms arrived here on a meteor or something similar. The implication of the claim is that life is not unique to Earth, and that life on other planets will be chemically similar to terrestrial life.

While it is considered a "fringe" theory with few adherents, a small number of scientists are studying meteorite fragments, looking for signs of microscopic alien life.