| A | B |
|---|
| index fossil | a fossil used to identify the relative age of a rock layer |
| trace fossil | forms when a footprint or trail trapped in mud or sand hardens to stone |
| carbon film | forms when leaves and stems are pressed between layers of soft mud or clay leaving a carbon imprint on rock |
| preserved remains | forms when entire organisms or parts are prevented from decaying and are trapped in rock, ice, tar, or amber |
| Permineralized (petrified) | forms when mineral soak into the remains, replace them, and changes them into rock |
| Mold | forms when sediments bury an organism, decays leaving a cavity in the shape of the organism |
| cast | forms when a mold is filled with sand or mud and hardens into the shape of the organism |
| law of superposition | states that rocks at the bottom are older and rocks at the top are younger |
| relative age | age of fossils or rocks compared to other fossils or rocks |
