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Superposition

LEARNING TARGET: 

Explain why younger layers of sedimentary rocks are on top of older layers.  Hypothesize about what geologic events could have caused huge blocks of horizontal sedimentary layers to be tipped, or caused older rock layers to be on top of younger rock layers.

 

FOCUS QUESTIONS: 

What are two different methods of determining the age of rocks?

What is the law of superposition?

 

KEY CONCEPT:grand canyon superposition

Sedimentary rocks are formed particle by particle and bed by bed, and the layers are piled one on top of the other. Thus, in any sequence of layered rocks, a given bed must be older than any bed on top of it. This Law of Superposition is fundamental to the interpretation of Earth history, because at any one location it indicates the relative ages of rock layers and the fossils in them.

super position

 

 

VOCAB:

Law of Superposition:  in undisturbed sedimentary rocks, each layer is older than the one above it, and younger than the laye below it.

Relative Age:  a comparison of age, such as if a rock or fossil is younger or older than something else.

Absolute Age:  the exact age of a rock, fossil, or geologic event.

Index Fossil:  fossils of organisms that lived during only one short period of time.

Fault:  a crack in the Earth’s crust along which rock formations move.

Intrusion:  magma that forces its way into or between other rock formations.

 

rock layers

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