Law of Superposition: Definition & Concept Video

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  • 0:01 What is Superposition?
  • 0:25 A Basic Principle of…
  • 1:23 Why Superposition is Useful
  • 1:55 When It Does & Doesn't Apply
  • 2:27 Lesson Summary
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Lesson Transcript
Instructor: Charles Spencer

Charles teaches college courses in geology and environmental science, and holds a Ph.D. in Interdisciplinary Studies (geology and physics).

Superposition is one of the fundamental principles of stratigraphy. It is also a statement of the obvious (or seems to be). You will learn all about the concept in this lesson.

What is Superposition?

Superposition is the name for the observation that given a stack of layers, or beds, of sedimentary rocks, older beds are found below younger beds (as long as there has been no disturbance of the beds). Although often referred to as law of superposition, it also is known as the principle of superposition.

A Basic Principle of Stratigraphy

The study of how sedimentary rock layers form and their relationships to one another is a branch of geology known as stratigraphy. Superposition is one of the four fundamental principles that geologists rely upon for interpreting the sequence of events that created a stack of sedimentary rock layers. The other three are original horizontality, lateral continuity, and cross-cutting relationships.

The idea was first formally applied to understanding sedimentary rocks in the late 1660s, by Nicolas Steno, a Danish Catholic bishop and scientist. He surmised that layers of sedimentary rock formed from sediment that settled out of water over time in horizontal layers, what we call the principle of original horizontality. Based on that premise, he concluded that unless the layers of sediment or the resulting beds of rock were somehow overturned or otherwise disturbed following deposition, older rock layers would always be found below younger ones in a layer-cake sequence of beds.

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