hammegk said:
As to abiogenesis, the current answer is "we have no clue". I do find it interesting that apparently it was a one-of event on earth.
Actually, we have a great many clues. It's not a totally solved question, but the RNA world model has been quite useful in terms of a whole field of study.
Those clues are yielding results.
And I don't think it was a unique event. Different parts of the process may have happened zillions of times. But the last time, it stuck, and we haven't seen *the entire process* repeated since. Parts of it happen all the time, though.
Remember, we aren't talking about a bunch of chemicals swirling in a pool and then ZAP, bacteria. We're talking about millions and millions of years of slow, incrimental change, step by tiny step, from simple non-living things to simple living things. At one end of the scale you have things that very certainly aren't alive, and on the other end you have things that absolutely are alive. In the middle (millions of years of middle!), you get a foggy, "well, it MIGHT be alive, in some aspects".
Why hasn't it happened again? Well, let's look at the question from the point of view of competition. Surely the most fit organism to survive would change the environment to the point where competing proto-organisms couldn't survive.
Things that eat rna, for example. Those would be able to populate the earth, and make sure that nothing got too far along behind it to compete!.
There are a lot (A LOT) of those microorganisms today, which eat amino acids (like RNA). So that's why the process hasn't repeated. Photoheterotrophs were among the very first life on earth, and they devour amino acids.
So nothing new gets started!
...)