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What could a geologist say about that section of rock?
Following the Principle of Original Horizontality, he could say that whatever forces caused the deformation, like an earthquake, must have occurred after the formation of all the rock strata.
Once we assume that all rock layers were originally horizontal, we can make another assumption: that the oldest rock layers are furthest toward the bottom, and the youngest rock layers are closest to the top. The forest layer is younger than the mud layer, right? When scientists look at sedimentary rock strata, they essentially see a timeline stretching backwards through history.
We're not so sure about the next layer down, but the one below it is 100 million years old. Not exactly, but we do know that it's somewhere between 70 and 100 million years old.
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.
There may be a layer missing in the strata, or a set of sedimentary rock on top of metamorphic rock.
These interfaces between discontinuous layers of rock are called unconformities.