Comment by kadoban

> If there is a different tree of life right here on Earth and we don't know about it, that would cast doubt on our ability to detect life in worlds light years away.

Hm, I don't think it does. The problem is vastly different. Here, on Earth the problem is: sift through all of life for some that's different than the rest. A _hard_ problem with how little of microscopic life we've cataloged completely and with how much of the volume of Earth we can't see.

The problem looking for life in the stars is more: find evidence of _any_ life, so radio signals or chemicals that can't reasonably come from anything else but biology. Those are hard as hell, but fundamentally different.

> Also, if life had multiple false starts here on Earth, that does also suggest that it is very difficult to take hold even on the original Goldilocks planet.

That would be interesting. I kind of guess it's less likely than some kind of winner-take-all outcompeting thing, but who knows. Life that we see is just very good at spreading, escaping and holding on tight.