Answered Dec 16, 2017
Thanks for the A2A.
The answer is (drum-roll, please…)
Nobody knows.
It was a really, really long time ago.
Perhaps, somehow, a little bubble in the water on a beach got some amino acids and nucleic acids (specifically RNA) into it. Those molecules may have formed from water (containing various stuff dissolved in it) dripping onto a rock that heated and cooled off each day.
Perhaps it arrived, frozen in the ice of a comet or meteorite, from some other planet.
Nobody knows, and there is probably zero way for anyone to ever know.
That sounds kind of “zen”, doesn’t it?