New York State High School Regents Exam Prep|
Words to Know to Interpret the Relative Ages of a Geologic Profile
Law of Superposition states that the rock layer on the bottom is the oldest and the layers get younger as you move up the profile. This is true for any undisturbed rock exposure.
Igneous Intrusions are formed when magma is injected into older rock layers in the crust. Therefore they are younger than the rock they are found in. Look for contact metamorphic rock in the layer above and below the intrusion.
Igneous Extrusions are rocks that formed from lava on the surface of the earth. They are younger than the rock layers below. Look for contact metamorphic rock on the bottom only.
Folds are bends in the rock layers. They occur after the rock layers formed.
Faults are cracks in the rock layers where some movement has taken place. Faults produce offset layers.
Unconformity, a buried erosion surface, is formed when an area of the crust was uplifted above sea level and then eroded. Some time after that the area subsided below sea level and new sediments were deposited on top of the eroded surface
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New York State High School Regents Exam Prep Center: Earth Science