How did life begin on Earth? originally appeared on Quora - the knowledge sharing network where compelling questions are answered by people with unique insights.
Answer by Richard Muller, Professor of Physics, UC Berkeley, author Energy for Future Presidents, on Quora.
We have no idea.
The building blocks of life as we know it are chemicals called amino acids. We know that they can form naturally, in lightning strikes and other energetic phenomena. But how did we get from amino acids to RNA, the fundamental unit of advanced life, is a complete mystery. How many times did that happen independently? Once? A zillion times? We don't know because we have no idea what the mechanism is.
Some people argue that it happened so rapidly on Earth, that the probability must be high. Therefore, there must be abundant life near other stars. But we really don't know. It is conceivable that the probability is so tiny, that if you plug it into Drake's equation you find that we expect life to have formed only once in the entire universe.
My own guess (and this is not a scientific theory) is that there was a precursor form of living molecule that was capable of carrying limited genetic information, much less than RNA, and still capable of reproducing. When RNA developed, the more primitive form of life could not compete, and was literally eaten up.
There is a science fiction story that illustrates this. A group of advanced computers rules the world. One little baby computer asks, "How did computers come to being?"
The mommy computer answers, "We don't really know. We can trace our beginnings back to a microprocessor that was first created in what we call year zero" [in human years, this corresponds to the late 1900s, but mommy computer doesn't know that], "but we can't conceive how that first microprocessor was created. It's too complex to have come about by chance. Maybe there was a primitive life form that preceded it, and which is now completely wiped out. Carbon is on the same part of the periodic table as Silicon, so some people think it might have been a carbon-based life form. But carbon doesn't make very good electronic circuits, so I think this idea is foolish."
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