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by astazangasta
2540 days ago
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Given the gaps in our knowledge of early life, a definite statement in either direction is unlikely to be in the offing. However, terrestrial life is decidedly unlikely. Life is decidedly unlikely, and no one has so far suggested an even remotely plausible mechanism for abiogenesis on Earth. This means if you are betting, an extraterrestrial origin is the safe bet; if the odds of abiogenesis are so slim, while life once formed is tenacious and hardy enough to travel through space, it is more likely life traveled here. |
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Panspermia might increase the window of time and set of planets where the abiogenesis of Earth's life could have occurred. But are there any grounded estimates of the factor by which it expands those windows? For example, is it safe to assume that if abiogenesis occurred on any planet in the Milky Way before the Earth formed, then samples of that life would have reached Earth within say 200M years after the Earth formed? That would require estimating the rates at which samples leave the planetary gravity well, how likely those samples are to reach Earth's gravity well, how likely the samples are to survive the trip, etc. I have not yet read any detailed estimates of this kind (but I'd like to!).
Another problem ... if the answer to the previous question is "yes", then that might expand the abiogenesis window by, say, 10^13 (say 200B planets and a 50-fold increase in the available time window, ignoring other galaxies). Is that enough to flip abiogenesis from "not likely" to "likely"? 10^13 is a big number but if abiogenesis is extremely unlikely then we're already dealing with very low probabilities. In other words, panspermia only helps if the probability of abiogenesis occurring on a planet in a given time window falls in a certain range, and in context that range might be quite narrow.