Relative age dating of sedimentary rocks
Free 5-day trial Discover how geologists study the layers in sedimentary rock to establish relative age.
Learn how inclusions and unconformities can tell us stories about the geologic past.
Since we assume all the layers were originally horizontal, then anything that made them not horizontal had to have happened after the fact.
We follow this same idea, with a few variations, when we talk about cross-cutting relationships in rock.
Let's say, in this set of rock strata, that we found a single intrusion of igneous rock punching through the sedimentary layers.
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Geologists use this type of method all the time to establish relative ages of rocks.
Now, what if instead of being horizontal, this rock layer was found in a tilted position?
How do we use the Law of Superposition to establish relative dates?
Let's look at these rock strata here: We have five layers total.