Geological and Biological Timescales

A key feature of the evolutionary sequence that we have sketched is that there must be sufficient time for natural selection to work through many successive generations. Until fairly recently in history, it was thought that the Earth was relatively young (in the most extreme estimates, only a few thousand years old). It has now become apparent that it is billions of years old, as is the Solar System in which it formed. This allows adequate time for the processes of chemical and biological evolution to work (see this biological and geological timescale for Earth).