Geologic Time/Dating Rocks and Fossils
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22 terms
Terms | Definitions |
|---|---|
 Uniformitarianism | same forces of change(water, earthquakes, etc) have been always present |
| Geological Time Scale | The summary of Earth's history, divided into intervals of time defined by major events of changes on Earth |
| Radioactive Dating | scientists can determine the age of ancient objects by using half-lifes of certain radioactive elements |
| Divisions of Geologic time | Eon, Ers, Period, Epoch |
| Precambrian Time | longest period of time |
| Paleozoic Era | the part of geologic time 570-245 million years ago ; invertebrates, fishes, amphibians, reptiles, ferns, and cone-bearing trees were dominant |
| Mesozoic Era | middle life (245-144 million years ago); rise of mammals and dinosaurs; the rise of birds; extinction of dinosaurs, rise of flowering plants |
| Cenozoic Era | era that began about 66 million years ago, known as the "Age of Mammals" |
| Relative Age | the age of something compared with other things |
| Absolute Age | the actual age of an event or object |
| half-life | length of time required for half of the radioactive atoms in a sample to decay |
| Law of Superposition | States that in a series of sedimentary rock layers, younger rocks normally lie on top of older rocks |
| index fossils | fossils that are widespread and lived in short periods of time |
| close in age | if the same index fossil is found in different parts of the world, it tells scientists that the rock layers are |
| unconformity | old eroded surface beneath newer sedimentary rock layers |
| fault | a break or crack along which rocks move |
| older | rock layers are always _______ than the faults they contain |
| intrusion | when magma forces its way into rock layers underground and hardens it forms an ____ |
| extrusion | when lava reaches he Earth's surface, the igneous rock that forms is an______ |
| younger | Extrusions are _______ than the rock layers beneath them |
| 4.6 billion years | the absolute age of the Earth |
| Fossils | traces or remains of living things from long ago |
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