Relative age dating also means paying attention to crosscutting relationships.
Say for example that a volcanic dike, or a fault, cuts across several sedimentary layers, or maybe through another volcanic rock type.
For example if you have a fossil trilobite and it was found in the Wheeler Formation.
The Wheeler Formation has been previously dated to approximately 507 million year old, so we know the trilobite is also about 507 million years old.
As a result, it was difficult to chronologically compare fossils from different parts of the world.
But, how can we determine how old a rock formation is, if it hasn’t previously been dated?
Scientists can use certain types of fossils referred to as index fossils to assist in relative dating via correlation.
Absolute dating entails laboratory analysis of rock samples that will take a longer time.
further, the dating results will still have to be cross-checked with mapping data.