The entire field of geology. The main methods are radiometric dating. There is no disagreement about an Earth billions of years old except for the subset of evangelicals who follow Price’s long debunked “flood geology”. Even many creationists understand the Earth is billions of years old. The rest are working off of a Bronze Age supposition.
So what does radiometric dating base it’s standard on? Sooner or later you will take a leap of faith. Keep going;)