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Comment by rpedela | Hacker News Reader

I generally don't like the assumption that life had to come from space because we don't know how life is created and it appeared so soon in the history of Earth. That is certainly a possibility, but it also possible that creating life from chemistry is easy. Just because we haven't figured it out yet doesn't mean it is hard. Obviously figuring out how it works is hard, but the mysterious mechanism may be simple.

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One problem I have with pan-spermia is: Why is there only one tree of life? Not several independent trees. If life evolved in one of the exo-planets, is not possible that several independent forms of life evolved in several planets and some ended up on Earth.

One tree (us) either appeared first and dominated resources, or we wiped our the other trees. Evolutionary forces work at levels above species. Two trees can compete with each other.

If this happened it did so at the microbe level. Physical evidence would be extraordinarily difficult. If we did find evidence of another tree it would be so 'alien' to our tree that might mistakenly call it extraterrestrial.

And since panspermia is necessarily done with microbes, they would get outnumbered and munched by our microbes if they arrived after our tree dominated our planet. Unless other planets happened to give birth to hardier, more virulent microbes, then welcome Andromeda Strain.

The individual nucleobases (cytosine [C], guanine [G], adenine [A] or thymine [T]) are made from the 4 most common elements, and appear to be modestly simple molecules. Is it so unbelievable that they naturally occur like methane or sodium glass?

I also don't subscribe to panspermia because first local origin must be reasonably proved unfeasible, but playing devil's advocate ¿what if our life tree outcompeted the others?

That's certainly possible, but not likely. Life began on Earth almost as soon as it was cool enough to do so, so we would expect to see life pop up over and over again. And it's highly unlikely that they would all get wiped out.

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