Joel Kontinen
A pair of Harvard astrophysicists had come up with this scenario;
Millions or billions of years ago, back when the solar system was more crowded, a giant comet grazed the outer reaches of our atmosphere. 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.
We could call it "interstellar panspermia," the seeding of distant star systems with exported life.
“We have no idea whether this ever actually happened –.and there's a mountain of reasons to be skeptical. 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.”
Elements are porous and they might really do enter and leave our solar system from time to time, and Siraj and Loeb's calculations show that it's plausible, maybe even likely, this has happened to large comets that graze Earth. Comets are porous, and might actually shield microbes from deadly radiation some microbes can survive a remarkably long time in space.
But how did they manage this? The origin of life is as difficult as always, in an evolutionary sense.
Source;
Letzter, Rafi. 2020. Physicists: Ancient life might have escaped Earth and journeyed to alien stars Live Science 30 January,
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