| A | B |
|---|
| Fossil | The preserved remains or traces of living things |
| Sedimentary rock | The type of rock that is made of hardened sediment |
| Mold | A hollow area in sediment in the shape of an organism or part of an organism |
| Cast | A solid copy of the shape of an organism |
| Petrified fossil | Fossils in which minerals replace all or part of an organism |
| Carbon film | An extremely thin coating of carbon on a rock |
| Trace fossils | Provide evidence of activities of organism, like foot prints |
| Paleontologist | Scientists who study fossils |
| Evolution | The gradual change in living things over time |
| Extinct | Something no longer exists and will never again live on this Earth |
| Relative age | The age of a rock compared to the age of other rocks |
| Absolute age | The number of years since the rock formed |
| Extrusion | Lava that hardens on the surface |
| Intrusion | Magma that pushes into layers of rock and hardens |
| Unconformity | A gap in the geologic record |
| Index fossil | Fossils that are widespread, existed for a short period of time and help geologists match rock layers |
| Atoms | Tiny particles that make all matter |
| Element | When all atoms in a particular type of matter are the same |
| Radioactive decay | The release of energy or decy of atoms over time |
| Half-life | The time it takes for half of the radioactive atoms to decay |
| Geologic time scale | A record off he life forms and geologic events in Earth's history |
| Eras | The three long units of time in the geologic time scale |
| Periods | The smaller units of time that eras are divided into |
| Continental drift | Forces inside Earth cause the continents to move very slowly over Earth's surface |
