Principle of relative dating

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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.Try It risk-free 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.As a member, you'll also get unlimited access to over 70,000 lessons in math, English, science, history, and more.

Now, what if instead of being horizontal, this rock layer was found in a tilted position?

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.

It sounds like common sense to you and me, but geologists have to define the Principle of Original Horizontality in order to make assumptions about the relative ages of sedimentary rocks. Say you have a layer of mud accumulating at the bottom of a lake. More sediment accumulates from the leaf litter and waste of the forest, until you have a second layer.

We'll even visit the Grand Canyon to solve the mystery of the Great Unconformity!

Imagine that you're a geologist, studying the amazing rock formations of the Grand Canyon.

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