the age of a rock compared to the ages of other rocks
the number of years since the rock was formed
law of superposition
in horizontal sedimentary rock layers the oldest layer is at the bottom. Each higher layer is younger than the layers below it
lava that hardens on the surface
when magma cools and hardens into a mass of igneous rock
a break in the Earth's crust
a gap in the geological record
a piece of rock that is contained in another rock
a fossil that is used to match rock layers; it must be widely distributed and represent a type of organism that existed only briefly
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