| A | B |
|---|
| geologic time scale | an outline of Earth's history |
| age of the earth | 4.6 billion years old |
| law of superposition | younger rock layer is on top of the older rock layers |
| relative dating | process of determining that one event happened before or after another event |
| fossil | a track, a trace, or the remains of organisms preserved in rock |
| extinct species | species that has no living members |
| index fossil | fossil of an organism that lived in many places over a short time period |
| half-life | amount of time needed for one-half of the radioactive atoms to decay |
| radiometric dating | technique that uses radioactivity to find the ages of certain rocks |
| era | largest division of geologic time |
| precambrian time | lasted over 4 billion years and represents 75% of earth's history |
| paleozoic era | first vertebrates and amphibians |
| mesozoic era | known as the age of the dinosaurs |
| cenozoic era | present age - mammals prominent |
| trilobites | index fossil dating to Paleozoic era |
| pangaea | land mass formed during Paleozoic Era |
| Appalachian mountains | begin to form during Paleozoic Era |
| bacteria and algae | Life forms during Precambrian time |
| Ice Ages | occurred late in the Cenozoic Era |
| ammonite | index fossil dating to Mesozoic Era |
