| Term | Definition |
| uniformitarianism | current geologic processes are the same that were at work in the past |
| catastrophism | processes that shaped the Earth were short, violent and occured in the past |
| absolute age | actual age of an object |
| relative age | age of an object compared to the ages of other objects |
| superposition | a layer of sedimentary rock is older than the one above it and younger than the one below it |
| unconformity | a break in the rock record |
| cross-cutting | a fault or intrusion is younger than the rock it cuts through |
| evolution | the change in living things over time |
| paleontology | the study of fossils |
| fossil | the remains or traces of an organism preserved in the rocks of the Earth's crust |
| index fossil | a guide fossil found in the rocks of one geologic age |
| era | largest unit of geologic time |
| period | subdivision of a geologic era |
| epoch | subdivision of a geologic period |
| vertebrate | animal with a backbone |
| invertebrate | animal without a backbone |
| Precambrian Era | earliest and longest geologic era |
| Paleozoic Era | geologic period that followed the Precambrian;means "ancient life" |
| Mesozoic Era | geologic era that followed the Paleozoic;means "middle life" |
| Cenozoic Era | the latest geologic era;means "new life" |