Scientists disagree about how life began - in space, in warm rock pools, in oceanic vents, on clays, and so on.
The evidence so far suggests that life on earth started as a single breakthrough cell after hundreds of millions of years of chemical evolution. This ancestor cell divided and diversified over the course of billions of years into the fantastic variety that we know today. We know they had a common origin, because all cells use the same type of RNA and DNA molecules for their genetic material - indeed a few genetic sequences are present in all living organisms.
"All the organic beings which have ever lived on this earth may be descended from some one primordial form," wrote Charles Darwin in The Origin of Species.
In a real sense all life on earth may be related as siblings, just as all humans appear to descend from a single family.
