It doesnt give an exact age but a relative (or comparison) age. Each layer will be successively younger or more recent. Superposition is the principle that says younger rocks lie above older rocks in an undisturbed sequence.This means that you know which events came first, but not the exact time when they happened. Scientists use the fossils of animals to help determine relative age.All dating methods today can be grouped into one of two categories: .
This is similar to what geologists do to determine age.
Amino acid dating: This relatively new form of absolute dating is useful in archaeology, anthropology, paleobiology, molecular biology and anything else that may study organic substances to pinpoint an actual date or define a date range.
It's found a great use in the tracking of human migrations in antiquity, demonstrating earlier arrival of humans into North America - pushing dates back from 15,000 years to 50,000 years (4).
Where are the oldest pictures, by year, going to be in your stack? Often igneous intrusions will cut across layers of rock.
The principle of cross-cutting relationships states that the intrusions are younger than the rock they cut.