Igneous rock and carbon 14 dating
Layers of rock are deposited horizontally at the bottom of a lake (principle of original horizontality).
According to the principle of original horizontality, these strata must have been deposited horizontally and then titled vertically after they were deposited.
Layers that cut across other layers are younger than the layers they cut through (principle of cross-cutting relationships).
The principle of superposition builds on the principle of original horizontality.
The age of the fossil must be determined so it can be compared to other fossil species from the same time period.
Understanding the ages of related fossil species helps scientists piece together the evolutionary history of a group of organisms.