Geology note quiz- Dating of Rocks, Fossils and geologic events
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36 terms
Terms | Definitions |
|---|---|
 geologic record | The division of Earth's history into time periods, grouped into three eons—Archaean, Proterozoic, and Phanerozoic—and further subdivided into eras, periods, and epochs. has youngest being on top and getting older as it goes down by layers |
| relative age dating | determines when something formed or happened in relation to other things; ex. younger brother by saying you are older than him |
| absolute age dating | process of determining when something formed or happened in exact units of time such as days, months or years ex. younger brother by saying he is 3 years younger than me |
| geologic time scale | a chart of named intervals of the geologic record and their ages in both relative and absolute time |
| rock units | 1) eonothem (largest) 2) erathem 3) system 4) series 5) Stage 6) zone |
| corresponding geologic time units | 1) eon of time (longest unit) 2) era of time 3) period of time 4) epoch of time 5) age of time 6) chron of time |
| subdivision | is based on color, texture, rock type, or other physical features of the rocks, and the mappable units called formations |
| formation | mappable units; can be subdivided into "members"-individual strata |
| contacts | surfaces between of any kind of units |
| 6 basic laws for determining relative age relationships | 1) Law of Original Horizontality 2) Law of lateral continuity 3) Law of superposition 4) Law of inclusions 5) law of cross-cutting 6) Law of unconformities |
| law of original horizontality | sedimentary layers (strata) and lava flows were originally deposited as relatively horizontal sheets; if they are no longer flat, it is because they have been displaced by subsequent movements of Earth's crust |
| law of lateral continuity | lava flows and strata extend laterally in all directions until they thin to nothing (pinch out) or reach the due of their basin deposition |
| law of superposition | in an undistributed sequence of strata or lava flows, the oldest layer is at the bottom of the sequence and the youngest is at the top |
| law of inclusions | any piece of rock (blast) that has become included in another rock or body of sediment must be older than the rock or sediment which it has been incorporated; such a blast is called an inclusion. The surrounding body of rock is called the matrix. an inclusion is older than its surrounding matrix |
| law of cross cutting | any feature that cuts across a rock or body of sediment must be older than the rock or sediment that cuts across; such features include fractures (cracks in rock), faults (fractures along which movement has occurred), or masses of magma that cut across preexisting rocks before they cooled. when a body of magma intrudes preexisting rocks, a narrow zone of metamorphism usually form in the preexisting rocks adjacent to the intrusion |
| law of unconformities | surfaces called unconformities represent gaps in the geologic record the formed wherever layers were not deposited for a time or else layers were removed by erosion an unconformity is a rock suface that represent a gap in the geologic record |
| three kinds of unconformities | 1) disconformities 2) angular unconformity 3) nonconformity |
| disconformity | an unconformity between parallel strata or lava flows; most are irregular surfaces and pieces of the underlying rock are often included in the strata above them |
| angular unconformity | is an unconformity between two sets of strata that are not parallel to one another |
| nonconformity | an unconformity between younger sedimentary rocks and subjacent metamorphic or igneous rocks |
| Principle of fossil Succession | fossil organisms succeed one another in a definite and determinable order, and any time period can be recognized by its fossil content |
| range zone | sequence of strata in which fossils of a particular organism are found |
| index fossils | organism whose range zones have been used to represent named divisions of the geologic time scale |
| periods and eras | how relative ages of rocks containing these fossils are presented 1) precambrian, cambrian period, ordovician, silurian, devonian, mississippian, pennsylvanian, permain, triassic, jurassic, cretaceous, paleogene, negogene, quaternay 2) precambrian,paleozoic, mesozoic, cenozoic |
| radiometric dating | way to measure the passage of time is by the regular rate of decay of radioactive isotopes; it is one way that geologists determine absolute ages of some geologic materials |
| isotopes | an element are atoms that have the same number of protons and electrons but different number of neutrons |
| parent isotope | the isotope that undergoes radioactive decay |
| daughter isotope | the stable isotope produced by the radioactive decay of the parent isotope |
| decay pair | a parent isotope and its corresponding daughter isotope |
| half-life | the time required for one half of the atoms of a radioisotope to emit radiation an decay products |
| decay pair formula | to determine the age of an object; percent of atoms that is parent atoms and daughter atoms must be measure with mass spectrometer; then find the number of half-lives that have elapsed and the object's corresponding age in number of half-lives. finally half-life for that decay pair |
| stratigraphy | study of strata (layers) in rocks two principles: 1) principle of original horizontality 2) principle of superposition |
| principle of original horizontality | it states that sediments are deposited under the influence of gravity as nearly horizontal beds; if folded or faulted strata, we know the the beds were deformed by tectonic forces after sediments were deposited |
| principle of superposition | it states that each layer of an undeformed sedimentary sequence is younger than the one beneath it and older than the one above it |
| principle of faunal succession | it states that the sedimentary strata in an outcrop contain fossils in a definite sequence |
| mass extinction | short intervals during which a large proportion of the species living at the time simply disappeared from the fossil record, followed by the blossoming of many new species |
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