Throughout the history of life, different organisms have appeared, flourished and become extinct.

principle of inclusion relative dating - Relative dating of rock layers worksheet

Different species of ammonites lived at different times within the Mesozoic, so identifying a fossil species can help narrow down when a rock was formed.

Correlation can involve matching an undated rock with a dated one at another location.

Suppose you find a fossil at one place that cannot be dated using absolute methods.

That fossil species may have been dated somewhere else, so you can match them and say that your fossil has a similar age.

Your goal is to study the smooth, parallel layers of rock to learn how the land built up over geologic time.

Now imagine that you come upon a formation like this: What do you think of it? How can you make any conclusions about rock layers that make such a crazy arrangement?

Some of the most useful fossils for dating purposes are very small ones.

For example, microscopic dinoflagellates have been studied and dated in great detail around the world.

Relative dating cannot establish absolute age, but it can establish whether one rock is older or younger than another.

Relative dating requires an extensive knowledge of stratigraphic succession, a fancy term for the way rock strata are built up and changed by geologic processes.

Correlation with them has helped geologists date many New Zealand rocks, including those containing dinosaurs.