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Numerical dating determines the actual ages of rocks through the study of radioactive decay.Relative dating cannot establish absolute age, but it can establish whether one rock is older or younger than another.Throughout the history of life, different organisms have appeared, flourished and become extinct.

Let's look at these rock strata here: We have five layers total.

Let's say we find out, through numerical dating, that the rock layer shown above is 70 million years old.

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

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Geologists have studied the order in which fossils appeared and disappeared through time and rocks. Fossils can help to match rocks of the same age, even when you find those rocks a long way apart.

This matching process is called correlation, which has been an important process in constructing geological timescales.

The highest layers tell them what happened more recently, and the lowest layers tell them what happened longer ago.

How do we use the Law of Superposition to establish relative dates?

In order to establish relative dates, geologists must make an initial assumption about the way rock strata are formed. sediments, which are deposited and compacted in one place over time.

It's called the Principle of Original Horizontality, and it just means what it sounds like: that all rock layers were originally horizontal. As you can imagine, regular sediments, like sand, silt, and clay, tend to accumulate over a wide area with a generally consistent thickness.

Learn how inclusions and unconformities can tell us stories about the geologic past.