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E Sci Ch 12
vocab
| Term | Definition |
|---|---|
| uniformitarianism | the forces and processes that we observe today have been at work for a very long time |
| relative dating | tells us the sequence in which events occurred, not how long ago they occurred |
| law of superposition | states that in an non deformed sequence of sedimentary rocks each bed is older than the ones above it and younger than the ones below it |
| law of cross-cutting relationships | anything that cuts across layers (faults, intruding magma) is younger than the affected rocks |
| unconformity | a gap in the rock record |
| angular unconformity | indicates pause in deposition, a period of deformation (fold/tilt), and then erosion occurs |
| disconformity | two sedimentary rock layers are separated by an erosional surface |
| nonconformity | when the ersoional surface separates older metamorphic rocks or intrusive igneous rocks from younger sedimentary rocks |
| fossils | remains/traces of previous life found in sedimentary rock |
| fossils form under... | quick burial and possession of hard parts |
| index fossil | fossils that are widespread geographically, are limited to a short span of geologic time, and occur in large numbers |
| index fossils allow geologists to... | help interpret/describe ancient environments (ex. mollusks=marine, palm tree=tropical) |
| correlation | establishing the equivalence of rocks of similar age in different areas |
| law of original horizontality | layers of sediment are generally deposited in a flat position |
| isotope | atoms of the same element with a different number of neutrons and therefore different mass number |
| radioactivity occurs when... | an isotope breaks apart and emits energy, aka radioactive decay |
| radiocarbon dating is used for... | the absolute dating of living things |
| carbon-14 comes from... | the atmosphere |
| carbon-14 gets to humans by | atmosphere-->plant-->animal-->human |
| half-life | the amount of time it takes for 1/2 of a unstable parent product to turn into a stable daughter product |
| The geologic time scale shows... | past geological events and changing life forms |
| how old is earth? | ~4.56 billion yrs |
| the geologic time scale bottom to top is... | oldest to youngest |
| divisions of the geologic time scale | eon-->era-->period-->epoch |
| divisions in the scale are determined by... | changes in living organisms |
| percentage of earth's history w/o life | 80% |
| radiometric dating | finds the absolute age of rocks and minerals |
| unaltered remains | remains of an organism that have barely changed over time |
| altered remains | remains changed over time; molds(hole) and casts (sand in hole); carbonization; petrification |
| indirect evidence | trace fossils (path of tail dragging on ground) |
| atomic number | number of protons in nucleus |
| mass number | protons plus neutrons |
Created by:
natbp13
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