So that brings up the question, if life happens so readily given the right conditions, how come it only happened once on earth? And I don't buy the explanation that one form out-competed all other forms -- given the diversity that we have now, there can be millions of forms of life all existing at the same place/time. But all instances we have now originated from one single biogenesis event.
So, how do we know that there was only one biogenesis, and not multiple ones that happen to resemble each other (i.e., that DNA-based life is the only thing that ends up working, and it occurred multiple times)? From what I gather, there are many markers in biological molecules, such as the direction certain molecules form (left vs. right, etc), and that multiple biogenesis events would have gotten these in random positions (i.e., your heart on the right side instead of the left side of the body).
> given the diversity that we have now, there can be millions of forms of life all existing at the same place/time.
Sure, each niche favors a different specialist, but why do you think that whichever process led to the emergence of life will be any good at producing competing specialists? I'd think that evolution of existing organisms would be infinitely better at this task, as existing organisms have both a numerical advantage and the strategic advantage of DNA (a "playbook" of previous successful strategies to draw inspiration from).
Very few niches are available for the emergence of life, even though there are clearly many available for the evolution of existing life. The available niches require a level of sophistication that spontaneous process cannot achieve but that evolution can achieve (e.g. photosynthesis).
Actually, given that our star is a third-generation star, you could even ask the question : why wasn't there life in our very own solar system before earth even existed ? Before sol started burning or even coalesce ?
The first generation stars wouldn't have had anything but hydrogen clouds surrounding them, but second generation stars would have had similar amounts of other elements to what we have today floating around them.
Given that "our" biogenesis event happened only the second time it could happen (here and in billions of other solar systems in our galaxy), where the hell are the second generation societies ? Didn't they survive the supernovas ? (possible, I suppose, but not exactly hopeful for our own chances of spreading across the stars). Was there some kind of large scale disaster ? But the question is worse than that, because they should have been spacefaring ... if they had anything like our numbers of satellites, we should have been able to find something, somewhere, right ?
So, how do we know that there was only one biogenesis, and not multiple ones that happen to resemble each other (i.e., that DNA-based life is the only thing that ends up working, and it occurred multiple times)? From what I gather, there are many markers in biological molecules, such as the direction certain molecules form (left vs. right, etc), and that multiple biogenesis events would have gotten these in random positions (i.e., your heart on the right side instead of the left side of the body).