How does evolution begin?
Probably some 3.8 billion years ago with the first proto-cells.
Origin of Life researchers now distinguish between very early "chemical evolution" and "biological evolution".
Chemical evolution occurred in the early oceans around 4 billon years ago and 4 steps were necessary for the first porto-cells to emerge:
1) emergence of biomolecules - which has now been demonstrated to be possible by at least 2 or 3 mechanisms - chemical evolution may have begun about here.
2) emergence of organized long-chain molecules - which also seems to have a number of ways this was accomplished. Clay minerals may have played a role at this stage.
3) emergence of self-replicating molecules - the precursors of RNA and DNA.
4) emergence of the first porto-cells and the shift to biological evolution - there was probably a number of early porto-cells at this time vying to become the first true "live cell" through natural or Darwinian selection.
Biological evolution probably took over around 3.8 billion years ago with the fittest single cell bacteria that could survive the anaerobic environments of early Earth.