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ES 9 Vocab 11
Unit 11: Historical Geology
| Term | Definition |
|---|---|
| Geologic time scale | list of major events in Earth's history that have been preserved in rock. Divided into Eon, Era, Period & Epochs. |
| Precambrian | longest era on Earth, over 4 billion years; Earth cooled, formed an atmosphere & slowly simple life in oceans began to appear |
| Era | 2nd largest unit of geologic time (minor changes in life of Earth). Divided into Periods. |
| Period | Often the smallest unit of geologic time (minor changes in life of Earth). Our current period is divided into Epochs. |
| Eon | largest unit of geologic time (before & after life). Divided into Eras. |
| Cenozoic | Age of Mammals-- Mammals (all types) rule Earth for ~ 65 million years so far |
| Mesozoic | Age of Reptiles-- Dinosaurs ruled Earth for ~ 180 million years |
| Extinct (extinction) | ALL members of a species are dead |
| Relative dating | comparison of rock layers to find out the order of events, but don't know exactly when they happened |
| Half-life | the amount of time it takes for 1/2 of the radioactive elements to decay into a daughter product. This amount of time i different for each radioactive element. |
| Radioactive dating | measuring the decay of radioactive elements to find out the exact age of a rock or fossil. |
| Fossil | evidence of earlier life preserved in rock |
| Cast | copy of original fossil, forms when ground water carrying minerals gets into the hole of a mold and fills it. |
| Mold | The depression or hold left in a rock when a fossil dissolves out. It shows the shape and surface of the original fossil |