Here are some of the methods and evidence that scientists use to put dates on events-
1. 'Radiometric dating' relies on half-life decay of radioactive elements to allow scientists to date rocks and materials directly.
2. 'Stratigraphy provides' a sequence of events from which relative dates can be extrapolated.
3. 'Molecular clocks' allow scientists to use the amount of genetic divergence between organisms to extrapolate backwards to estimate dates.