How did life on Earth start? No one knows. We know all about evolution and DNA replication, much more than our ancestors did, but we still have nothing but theories when it comes to explaining how nonliving matter ever started living. 

One theory says this process, abiogenesis, never happened on Earth at all. Life came to Earth fully formed as simple microbes from some other planet, then it spread and evolved. Earth has never had the conditions for abiogenesis as far as we can tell (whatever those conditions might be), but an alien planet could have those conditions.

Francis Crick—Nobel prize winner and part of the team who first observed the structure of DNA—weighed in on the subject in 1973. The idea that spores from a different planet just happened to make their way to Earth ("panspermia") is too unlikely, said Crick. But you know what he said is a lot more likely, and which we have to consider? A theory dubbed "directed panspermia": Aliens seeded life on Earth on purpose. 

His logic for this goes roughly as follows. Germs or spores would not be able to survive the trip here through space on their own. But an advanced civilization (including ours, given a little more tech) could build spacecraft to protect these microbes and direct them to distant planets. The process would take millions of years, outliving the species who launched the craft, but that's fine, because we're talking about the lifespan of the universe here and have billions of years to work with.

Crick also had some more specific arguments beyond this speculation (at one point in his paper, he says, "the psychology of extraterrestrial societies is no better understood than terrestrial society," realizing his reasoning is getting kinda "out there"). Life evolved to require such rare elements as molybdenum, which would make more sense if it started somewhere in which that element was more common. Also, Crick discovered that all life shares a universal genetic code, which is odd but would make sense if we all evolved from one kind of germ that infected our planet. That germ's home planet, however, probably had numerous separate very different genetic codes. 

We're all comforted to learn that aliens might have sent life to Earth, like in Prometheus. As for whether we should turn ourselves into alien progenitors and start seeding distant planets, Crick said no. No, at least not until we learn for sure whether those planets already have life on them. 

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For more on the mystery of life, check out:

The 7 Most Mind-Blowing Places Science Has Discovered Life

5 Reasons You Should Be Excited About Mars Today

Heavy Metal Albums Accurately Depict the Beginning of Life

Follow Ryan Menezes on Twitter for more stuff no one should see. 

Top image: 20th Century Studios

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