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