Science & Technology

The Panspermia Theory Says Humans Are From Outer Space

Are humans from outer space? It doesn't have the ring of a good question, but bear with us. Of course, Homo sapiens didn't arrive on Earth in spaceships. We evolved here, from Homo erectus, about 200,000 years ago. Homo erectus, in turn, originated roughly a million years ago, solidly on Earth. So we have a long history on this planet. The thing is, we can't trace it all the way back to the beginning. The origins of life on Earth are shrouded in confusion, so much so that some scientists wonder — to other scientists' chagrin — if it started here at all.

Related Video: Did Life on Earth Come from Space?

Why Would Life on Earth Have Started ... off Earth?

Occam's Razor — that is, the simplest explanation — does suggest that life on Earth would start on Earth, but there are issues with this assumption. Life on this planet emerged roughly 4 billion years ago and seems to have overlapped with a period of "heavy bombardment," when the Earth was getting hit with a lot of meteors. Some theorize that any life that emerged during this period would have died because, well, meteors are no joke.

Take the meteor that snuffed out the dinosaurs. (It arrived long after the bombardment phase, but it's a decent example.) This meteor was the size of Mount Everest, traveling "twenty times faster than a bullet," and it hit Earth so hard, it made the surface of the planet hotter than the sun, according to Peter Brannen's "The Ends of the World." The heat may have been momentary, but it was impossible to survive.

So, in light of the bombardment we got when we were just microbes, how are we here? According to the Panspermia theory, the very meteors that snuffed out the first signs of life on Earth had been carrying signs of life on board.

Tiny Interplanetary Hitchikers

Bacterial spores could, theoretically, survive hitching a ride through outer space on a meteor, potentially for thousands of years. These hardy, microscopic beings go into sleep mode when they can't access nutrients, but reanimate once they're in a hospitable environment. Sure, like all life, they can die. But they're not particularly prone to it.

For instance, scientists have found that spores of an oceanic algae, Nannochloropsis oculata, could hypothetically survive a meteor crash. The researchers shot algae-imbued rock-and-ice pellets into water at meteoric velocities — think 4 miles per second — and the spores didn't all die. (Of course, more died at higher speeds than at lower ones.) Another study found that the spores of Bacillus subtilis, a bacteria found in soil, could survive outer space conditions if they were shielded from UV radiation, as they would be inside a meteor. The study didn't run for the millennia it might take a meteor to reach earth, but some spores did survive for six full years.

Of course, for the Panspermia theory to work, the spores would still have to come from somewhere, and we have yet to find life on a planet besides our own. But it's highly unlikely we're alone in the universe, just statistically speaking, and space seems hospitable. Not to humans, but to life in general. Plenty of space detritus has carbon compounds in it, and carbon is foundational to life as we know it. So is water, which we've already found on Mars. (Frozen, but still.)

The Panspermia theory remains far from proven, but it's almost comforting to think about. Movies, not to mention some strains of science, present aliens as sinister outsiders — but maybe they're really our forefathers.

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Learn more about the search for alien life in "The Eerie Silence: Renewing Our Search for Alien Intelligence" by Paul Davies. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.

Written by Mae Rice July 6, 2018

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