| A | B |
|---|
| Absolute Age | The age of a rock given as the number of years since the rock formed. |
| Carbon Film | A type of fossil consisting of an extremely thin coating of carbon on rock. |
| Extrusion | An igneous rock layer formed when lava flows onto Earth's surface and hardens. |
| Fossil | The preserved remains or traces of living things. |
| Index Fossil | Fossils of widely distributed organisms that lived during only one short period. |
| Intrusion | An igneous rock layer that formed when magma hardens beneath Earth's surface. |
| Law of Superposition | The geologic principal that states that in horizontal layers of sedimentary rock each layer is older than the one above it and younger than the one below it. |
| Original Horizontality | Layers of sediment are orginally deposited horizontally |
| petrified fossil | A fossil in which minerals replace all or one part of an organism. |
| relative age | The age of a rock compared to the ages of rock layers. |
| trace fossil | A type of fossil that provides evidence of the activities of ancient organisms. |
| unconformity | A place where an old, eroded rock surface is in contact with a newer rock layer. |
| uniformitarianism | It states that the geologic processess that operate today also operated in past. |
| Cast | A fossil that is a copy of an organism's shape, formed when minerals seep into a mold. |
| Geologic Time Scale | A record of the geologic events and life forms in Earths history. |
| Mold | A fossil formed when an organism buried in sediemtn dissolves, leaving a hollow area. |
| Paleontologist | A scientist who studies fossils to learn about organisms that lived long ago. |
