Science Chapter 9: Clues to Earth's Past
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13 terms
Terms | Definitions |
|---|---|
 Fossil | Remains, imprints, or traces prehistoric organisms |
| Mold | A cavity left behind when the hard part of an organism decays or dissolves |
| Cast | A copy of an organism made when mineral-rich sediment or water enters a cavity and solidifies |
| Index fossil | The remains of species that existed on Earth for relatively short periods of time, were abundant, and were widespread |
| Carbon film | A thin film left behind from the original organism |
| Principle of superposition | In undisturbed layers of rock, the oldest rocks are on the bottom and the rocks become progressively younger toward the top |
| Relative age | The age in comparison to the ages of other things |
| unconformity | Gaps in rock sequences caused by erosion or a pause in deposition: there are 3 major kinds: nonconformity, angular unconformity, and disconformity |
| Absolute age | The age, in years, of a rock or other object |
| Radioactive decay | The process of breaking down isotopes |
| Half-life | The time it takes for half of the atoms in the isotope to decay |
| Radiometric dating | The process used to measure the ratio of a parent isotope to a daughter product in a mineral |
| uniformitarianism | The principle that Earth processes occurring today are similar to those that occurred in the past - "the present is the key to the past." |
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