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

4) tilting- when rock layers slant

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.