The basic methodology that covers all research into past events.
This is a question born of ignorance, and mischief.
There isn't a "basic methodology" for this.
There are several very clever very complicated methodologies.
Usually more than one methodology is used to corroborate the findings of another methodology.
Peer review soon picks holes in published findings that don't stack up - current science is always highly competitive.
Some of the methods in evolutionary biology and palaeontology include:
1.) Morphological progressions in fossils.
2.) Radiometric dating.
3.) Geological strata.
5.) Species dispersion.
7.) Genetic clocks.
8.) Molecular phylogenetics (genetic sequence comparisons).
Historians and Archaeologists have even more clever methodologies to work with.
The way to answer your question, SkyWriting, is for you to read the methods in some research papers and show some respect for the amazing sleuth work that goes into these matters. Research into the past is not just a random art of bum-plucking a date that sounds right - its highly rigorous and calibrated against vast tracts of prior knowledge that has passed peer review.