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Earth History Vocab
Earth Science, Earth History Unit, Chapters 8-9
| Term | Definition |
|---|---|
| principle of uniformitarianism | the same geologic processes occur today as occurred in the past |
| strata | rock layer |
| relative age | the age of an object in relation to the ages of other objects |
| law of superposition | a rock layer is older than layers above it and younger than layers below it, oldest layers on bottom, youngest layers on top |
| principle of original horizontality | sedimentary rock layers form in horizontal rows |
| unconformity | a break in the geologic record due to erosion |
| fault | a crack or break in rock layers, the Earth's crust can shift along this break |
| intrusion | igneous rock that forms when magma is injected into pre-formed rock layers, then hardens |
| law of crosscutting relationships | a object, like a fault or intrusion, is younger than the rock layers that it cuts through |
| absolute age | absolute, numeric age of an object |
| varve | a pair of sedimentary rock layers deposited annually |
| isotope | atoms of the same element that contain different numbers of neutrons |
| radioactive isotope | an isotope whose nucleus emits particles at a constant rate |
| radiometric dating | a method of determining the absolute age of an object by comparing percentages of radioactive (parent) isotope and stable (daughter) isotope |
| parent isotope | original radioactive isotope |
| daughter isotope | newly-formed stable isotope |
| half-life | the time required for half of a sample of radioactive parent isotope to be converted into stable daughter isotope |
| fossil | the trace or remains of an organism that lived long ago |
| paleontology | the study of fossils |
| mold | empty space left by an organism after it decayed |
| cast | sand or mud fills a mold, then turns to rock |
| coprolite | fossilized poop |
| gastrolith | fossilized stone from the stomach of a dinosaur |
| trace fossil | fossilized mark that formed is sedimentary rock that provides evidence of animal movement - footprints, burrows, nests |
| index fossil | a fossil that is used to establish absolute age of rock layers because it is unique, abundant, widespread, and only existed for a short span of geologic time |
| geologic column | an ordered arrangement of rock layers that is based on the relative age of the rocks |
| eon | longest division of geologic time |
| era | smaller division of an eon |
| period | smaller division of an era |
| epoch | smaller division of a period, not always present |
| age | smallest division of geologic time |
Created by:
jrobinson214
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