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unit 7
| Term | Definition |
|---|---|
| uniformitarianism | a principle that geologic processes that occurred in the past can be explained by current geologic processes. |
| fossil | the trace or remains of an organism that lived long ago, most commonly preserved in sedimentary rock. |
| trace fossil | a fossilized structure, such as a footprint or a coprolite, that formed in sedimentary rock by animal on or within soft sediment. |
| climate | the weather condition in an area over a long period of time. |
| ice core | a long cylinder of ice obtained from drilling through ice caps or ice sheets; used to study past climates |
| relative dating | any method of determining whether an event or object is older or younger than other events or objects is older or younger than other events or objects |
| superposition | a principle that states that younger rocks lie above older rocks if the layers have not been disturbed. |
| unconformity | a break in geologic record created when rock layers are eroded or when sediment is not deposited for a long period of time. |
| geologic column | an ordered arrangement of rock layers that is based on the relative ages of the rocks and in which the oldest rocks are at the bottom. |
| absolute dating | any method of measuring the age of an even or object in years. |
| radioactive decay | the process in which radioactive isotope tends to break down into a stable isotope of the same element or another element. |
| half-life | the time required for half of a sample of a radioactive isotope to break down by radioactive decay to form a daughter isotope. |
| radiometric dating | a method of determining the absolute age of an object by comparing the relative percentages of a radioactive parent isotope and a stable daughter isotope. |