Space.com 0 9/22/13, Megan Gannon

Scientists have long debated the possibility of that the microbial seeds of life did not originate on Earth, but were perhaps delivered here from an alien source, encased in comets or meteorites from Mars.

But to get here, simple life forms would have had to endure a litany of harsh cosmic conditions, including ejection into space, freezing temperatures, fiery re-entry and impact.

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