Geologists establish the age of rocks in two ways: numerical dating and relative dating.Numerical dating determines the actual ages of rocks through the study of radioactive decay.This term refers to the relation of one stratigraphical unit to another, by petrological, osteological, lithographic, cultural, chronological, or palaeontological means.For example, stratigraphic units may be correlated using palaeontological criteria, methods, and position relative to the glacial-interglacial cycle by examining physical and biological attributes.Correlation of fossil inclusions is a principle of stratigraphy: that strata may be correlated based on the sequence and uniqueness of their floral and faunal content.
The main relative dating method is stratigraphy (pronounced stra-TI-gra-fee), which is the study of layers of rocks or the objects embedded within those layers.
We'll even visit the Grand Canyon to solve the mystery of the Great Unconformity!
Imagine that you're a geologist, studying the amazing rock formations of the Grand Canyon.
Since certain species of animals existed on Earth at specific times in history, the fossils or remains of such animals embedded within those successive layers of rock also help scientists determine the age of the layers.
Similarly, pollen grains released by seed-bearing plants became fossilized in rock layers.