(NEWSER) – Two astrobiologists have a new explanation for why we haven't found alien life: It didn't evolve quickly enough to keep its planet habitable. "Most early planetary environments are unstable," Aditya Chopra says in a press release.

"To produce a habitable planet, life forms need to regulate greenhouse gases, such as water and carbon dioxide, to keep surface temperatures stable." For example, Venus and Mars may have had life at one point, but that life didn't evolve fast enough to keep the planets from heating and cooling past the point of habitability. Or—as Rachel Feltman at the Washington Post puts it—you can blame climate change; only in this case lifeforms didn't enact enough of it.

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