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Relative and Absolute Ages of Rocks Quiz Study Guide
relative dating- used in geology to determine the comparative age of rocks by examining the
position of the rock layers. i.e. top layers are younger than bottom layers, bottom layers are
older than top layers, etc.
relative age- a rock’s age compared to the ages of other rocks (not an exact age)
absolute age- the number of years since the rock formed; sometimes geologists can determine
the absolute age of the rock within a certain number of years.
law of superposition- states that for undisturbed rock layers,
the oldest rocks are on bottom and become younger and
younger toward the top.
extrusion- lava that hardens on the earth’s surface; always
younger than the rocks below it
intrusion- magma that cools and hardens in a mass of igneous
rock below the earth’s surface; always younger than the rock
layers around and beneath it
unconformity- gaps in rock layers; a place where new rock layers
meet much older rock surface beneath them
fault- a break in the earth’s crust
unconformity
index fossil- used to help geologists tell the relative ages of the rock
layers in which they occur
3 criteria:
lived on earth for short period of time
widespread geographically (everywhere)
abundant ( a lot of them)