| A | B |
|---|
| superposition | this principle states that the rocks on the bottom are the oldest and the rocks get younger as you go toward the top |
| unconformities | when there are gaps caused by erosion |
| principle of cross cutting | this principle states that an igneous intrusion is always younger than the rocks it has cut across |
| radioactive decay | scientists use this to find absolute age of rocks |
| beta and alpha | types of radioactive decay |
| parent isotope | this type of isotope is radioactive |
| half life | time it takes for half of the parent isotope to turn into the daughter isotope |
| 4.6 billion years | the Earth is how old? |
| fossils | the remains, imprints, or traces of prehistoric organisms |
| carbon films | this type of fossil preservation leaves a thin carbon silhouette of the organism |
| marine organisms | main type of fossils in Virginia |
| index fossils | the remains of species that existed on Earth for relatively short amounts of time, were abundant, and wide-spread |
