The origin of life

The origin of life consisted of events on a molecular scale and cannot be studied in the fossil record; but the record is valuably informative about timing.

The Earth itself is about 4.5 billion years old, and for the first few hundred million years it was far too hot to support life. The earliest fossil evidence for life is about 3.5 billion years old, and comes from some of the oldest rocks on the planet. They are already cellular and presumably descended from a long period (probably hundreds of millions of years) of prior evolution.

The striking fact about the evidence is that it suggests a very early time of origin for life: we can infer that life originated almost as soon as the physical conditions of the Earth permitted it. Does this mean that the origin of life, from non-living chemical raw materials, is an evolutionarily easy step?

The image opposite is of fossilized cyanobacterium found in Greenland and dating from the Upper Proterozoic, some two billion years ago.