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Radiometric dating rock strata

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In this lesson, we'll learn a few basic principles of stratigraphic succession and see whether we can find relative dates for those strange strata we found in the Grand Canyon.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.

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The same idea applies to fault lines that slide rock layers apart from each other; a fault that cuts across a set of strata must have occurred after the formation of that set.As a member, you'll also get unlimited access to over 70,000 lessons in math, English, science, history, and more.Plus, get practice tests, quizzes, and personalized coaching to help you succeed.Geologists find the cross-cutting principle especially useful for establishing the relative ages of faults and igneous intrusions in sedimentary rocks.Sometimes, geologists find strange things inside the strata, like chunks of metamorphic or igneous rock.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.

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.

These items are called inclusions - foreign bodies of rock or mineral enclosed within another rock.