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Learn about relative dating, the principles of superposition, and the geologic column. Understand the different types of disturbed rock layers and unconformities. Discover how to determine the sequence of events in Earth's history.
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Sci. 3-2 Relative Dating: Which Came First? Pages 59- 63
A. Relative Dating- determining whether an object or event is older or younger than other objects or events.
B. The Principle of Superposition- states that younger rocks lie above older rocks as long as the rocks have not been disturbed.
C. Geologic Column- an ideal sequence of rock layers that contains all the known fossils and rock formations on Earth arranged from oldest to youngest.
D. Disturbed Rock Layers 1) fault- a break in the Earth’s crust along which blocks of crust slide relative to one another.
2) Intrusion- molten rock that squeezed into existing rock and hardened
3) Folding – when rocks bend and buckle from Earth’s internal forces
Unconformities- when a layer or several layers of rocks are missing from a rock layer sequence, a gap • 1)Means missing time, time not recorded by rock layers
Types of Unconformities • 1) Disconformity- exists where part of a sequence of parallel rocks layers is missing ( Hard to see, most common)
2) nonconformity- exists where sedimentary rock layers lie on top of an eroded surface of nonlayered igneous or metamorphic rock.
3) angular unconformity- exists between horizontal rock layers and rock layers that are tilted or folded. The tilted or folded layers were eroded before the horizontal layers formed above them.