Well I'm only 14 but this is what I know, my because is a scientist. Well if it is found in the Grand Canyon or a place that the rock is layered then they could go by that the the lower the layer then the older it is one layer takes thounds over years and the can detrimant by that. They also can by identifying the animal and if distent how long ago and base it on that too. But the main why they do it is Carbon dating, the put carbon and the object with in the mashin and the mashin then anlizeys it and prints out a result but it is also much more complicated I just can't talk bout it. Lab rules
Carbon dating. I'm not a scientist and I'm not sure how it is done, but I know ages are determined with this.