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Geologic time scale
Earth Science
| Question | Answer |
|---|---|
| Eon | measured in billions of years, is the longest time unit of the geologic time scale |
| Era | defined by the differences in life-forms found in rock and measured in hundreds of millions to billions of years, is the second-longest span of time on the geologic time scale |
| Period | measured in tens of millions of years before present. are defined by the life-forms that were abundant or became extinct during the time in which specific rocks were deposited |
| Epochs | smaller divisions of geologic time and are usually measured in millions of years to tens of millions of years |
| Relative dating | estimating the dates of rocks and fossils according to the other rocks and fossils around it |
| Absolute dating | Determining the age of rocks and fossils by doing tests to get the exact age |
| Uniformitarianism | states that processes that have been occurring today such as weathering and mountain building have been occurring since the Earth formed |
| Methods for relative dating: | 1.Law of Superposition 2.Cross-cutting relationships 3.Unconformity 4.Correlation |
| Law of Superposition | In a rock sequence, the oldest rocks are located at the bottom and the youngest are at the top |
| Cross-cutting relationships | states that an intrusion or a fault is younger than the rock it cuts across |
| Unconformity | is a gap in the rock record usually caused by an erosional surface becoming buried by the deposition of younger rocks |
| Correlation | the matching of outcrops of one geographic region to another |
| Absolute dating methods | 1.Radioactive Decay 2.Radiometric Dating 3.Half-life 4.Tree Rings 5.Seasonal Climatic Changes 6.Distinctive Sediment Layers |
| Fossils | Evidence of once living material |
| Altered hard parts | When the Hard parts of an organism have been removed and replaced with minerals |
| Molds | the impression that organisms leave in rocks |
| Casts | when molds are filled in with minerals |
| Index fossil | the remains of a plant or animal that can be used to correlate rock layers or to date particular rock layers |
| Trace fossils | Indirect evidence of plant and animal life |
Created by:
elarocco
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