A series of experiments using small rockets in the 1970s found colonies of bacteria in the upper atmosphere. While the study's concept may seem far-fetched, humanity is constantly confronted with seeming impossibilities, like Earth going around the sun, or quantum physics, or bacteria hitching a ride into the galaxy aboard a comet - that turn out to be true, Siraj saidĪnd there's been reason to suspect that it might be possible. Siraj told Live Science that although a lot more work needs to be done to back up the finding, it should be taken seriously - and that the paper may have been, if anything, too conservative in its estimate of the number of life-exporting events. But in a new paper, Amir Siraj and Avi Loeb, both astrophysicists at Harvard University, argue that at least the first part of this story - the depositing of the microbes into a comet that gets ejected from the solar system - should have happened between one and a few dozen times in Earth's history. We have no idea whether this ever actually happened –.and there's a mountain of reasons to be skeptical. You could call it "interstellar panspermia," the seeding of distant star systems with exported life. Eventually, the object crashed into one of those planets, deposited the microbes - a few of them still living - and set up a new outpost for earthly life in the universe. Tens of thousands, maybe millions, of years passed before the comet ended up in another solar system with habitable planets. These microbes ended up embedded deep within the comet's porous surface, protected from the radiation of deep space as the comet rocketed away from Earth and eventually out of the solar system entirely. Extremely hardy microbes were floating up there in its path, and some of those bugs survived the collision with the ball of ice. It was moving fast, several tens of miles above the Earth's surface - too high to burn up as a fireball, but low enough that the atmosphere slowed it down a little bit. Millions or billions of years ago, back when the solar system was more crowded, a giant comet grazed the outer reaches of our atmosphere.
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