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How Did We Get Here? Panspermia

Panspermia (Greek: πανσπερμία from πᾶς/πᾶν (pas/pan) “all” and σπέρμα (sperma) “seed”) is the hypothesis that life exists throughout the Universe, distributed by meteoroids, asteroids, and planetoids.

Panspermia proposes that life that can survive the effects of space, such as extremophile bacteria, become trapped in debris that’s ejected into space after collisions between planets that harbor life and Small Solar System Bodies (SSSB). Bacteria may travel dormant for an extended amount of time before colliding randomly with other planets or intermingling with protoplanetary discs. If met with ideal conditions on the new planets’ surfaces, the bacteria become active and the process of evolution begins. Panspermia is not meant to address how life began, just the method that may cause its sustenance. (A variation of the panspermia hypothesis is necropanspermia which is described by astronomer Paul Wesson as follows: “The vast majority of organisms reach a new home in the Milky Way in a technically dead state … Resurrection may, however, be possible.”)

The related but distinct idea of exogenesis (Greek: ἔξω (exo, “outside”) and γένεσις (genesis, “origin”)) is a more limited hypothesis that proposes life on Earth was transferred from elsewhere in the Universe but makes no prediction about how widespread it is. Because the term “exogenesis” is more well-known, it tends to be used in reference to what should strictly speaking be called panspermia.