| A | B |
|---|
| fossil | preserved remains or traces of living things |
| theory of evolution | groups of organisms change over time |
| law of superposition | if undisturbed, the bottom layer of rock is older than the top layer |
| relative age | age of rock compared to the ages of other rocks |
| absolute age | # of years since the rock formed |
| radioactive dating | used to determine the absolute age of rocks |
| half-life | time it takes for half the radioactive atoms to decay |
| intrusion | when magma pushes into a body of rock |
| index fossil | organism that existed briefly & widely distributed - used to date rocks |
| extinct | group of organisms that no longer exists on Earth |
