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Unit 5 Geologic Time
HS Earth Space Science
| Term | Definition |
|---|---|
| absolute dating | A technique used to determine the actual age of a fossil |
| Cambrian explosion | rapid diversification of most major animal groups marking the start of the Paleozoic era |
| cast | A type of fossil that forms when a mold becomes filled in with minerals that then harden |
| Cyanobacteria | Photosynthetic |
| Eons | The largest division of time on the geological scale. |
| Epochs | the smallest units of geologic time and last several million years |
| era | a long and distinct period of history with a particular feature or characteristic. |
| Evolution | Change in a kind of organism over time; process by which modern organisms have descended from ancient organisms. |
| Fossil | The preserved remains or traces of an organism that lived in the past |
| Geologic Time Scale (GTS) | the division of Earth history into blocks of time--eons |
| half-life | The time required for one half of the atoms of a radioisotope to emit radiation an decay products |
| index fossil | a fossil that is useful for dating and correlating the strata in which it is found. |
| Law of Superposition | The geologic principle that states that in horizontal layers of sedimentary rock |
| mass extinction | event during which many species become extinct during a relatively short period of time |
| meteorite | A meteoroid that passes through the atmosphere and hits Earth's surface. |
| mold | A type of fossil formed when a shell or other hard part of an organism dissolves |
| Periods (GTS) | significant divisions of time within an Era |
| permineralized fossil | forms when organisms decompose extremely slowly. dissolved minerals gradually infiltrate the interior of cells and harden into stone |
| Precambrian Era | Earth's first era that began 4.6 billion years ago that includes creation of the Sun |
| Precambrian shield | Continental core of Archean and Proterozoic rock that may be exposed at the surface or buried by sedimentary rocks. |
| radioactive decay | the process in which a radioactive isotope tends to break down into a stable isotope of the same element or another element |
| radiocarbon dating | method for determining age by comparing the amount of carbon-14 to the amount of carbon-12 in a sample |
| radiometric dating | method used to determine the age of rocks using the rate of decay of radioactive isotopes |
| relative dating | Method of determining the age of a fossil by comparing its placement with that of fossils in other layers of rock |
| trace fossil | A type of fossil that provides evidence of the activities of ancient organisms |
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