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CHAPTER 8 VOCABULARY
| Term | Definition |
|---|---|
| Geology | Study of the structure of planet Earth and the forces that make and shape Earth. |
| Uniformitarianism | Geologic processes that operated today also operated in the past. |
| Igneous Rocks | Form when molten material beneath Earth's surface cools and hardens. |
| Sedimentary Rocks | Made of sediments that have been deposited and then pressed together. |
| Metamorphic Rocks | Form when an existing rock is changed by heat, pressure, or chemical reactions. |
| Rock Cycle | A series of processes on and beneath Earth's surface that slowly change rocks from one kind to another. |
| Magma | Molten material beneath Earth's surface. |
| Lava | Magma that flows to the surface. |
| Relative Age | The age of a rock compared to the ages of other rocks. |
| Absolute Age | The number of years since the rock formed. |
| Law of Superposition | In horizontal rock layers, the oldest is at the bottom and the youngest is at the top. |
| Extrusion | Lava that hardens on the surface. |
| Intrusion | Igneous rock formed when magma cools and hardens. |
| Fault | A break in Earth's crust. |
| Unconformity | The surface where new rock layers meet a much older rock surface beneath them. |
| Inclusion | A piece of rock contained in another rock. |
| Index Fossil | A widely distributed organism that existed briefly. |
| Atom | The small particles that make up matter. |
| Element | When all atoms in a particular type of matter are the same. |
| Radioactive Decay | The process in which the atoms of one element break down to form atoms of another element. |
| Half Life | Time it takes for half of the radioactive atoms to decay. |
| Erosion | Process in which natural processes break down rocks and carry away the pieces. |
| Geologic Time Scale | A record of life forms and and geologic events in Earth's history. |
| Era | Three long units between Precambrian and present. |
| Period | Subdivision of era. |
| Invertebrates | Animals without backbones. |
| Vertebrates | Animals with backbones. |
| Amphibian | Animal that lives on land and water. |
| Reptile | Vertebrate with scaly skin and leathery, tough shelled eggs. |
| Mass Extinction | Event in which many different organisms die at the same time. |
| Mammal | Warm blooded vertebrate that feeds its young milk. |