To determine the relative age of different rocks, geologists start with the assumption that unless something has happened, in a sequence of sedimentary rock layers, the newer rock layers will be on top of older ones. This rule is common sense, but it serves as a powerful reference point.
Geologists draw on it and other basic principles ( to determine the relative ages of rocks or features such as faults.
In a way this field, called geochronology, is some of the purest detective work earth scientists do.
There are two basic approaches: relative age dating, and absolute age dating.
Have you ever wondered how the scientists knew the age of the bone?
Part 2 explains how scientists run into problems when they make assumptions about what happened .
An hourglass is a helpful analogy to explain how geologists calculate the ages of rocks.
Scientists can use certain types of fossils referred to as index fossils to assist in relative dating via correlation.
Index fossils are fossils that are known to only occur within a very specific age range.