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93 Cards in this Set
- Front
- Back
Law of Superposition |
in undistubed layers of sedimentary rock, the oldest is on the bottom, and the youngest is on the top. |
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Cross-cutting |
A principle of relative dating. A rock or fault is younger than any rock (or fault) through which it cuts. |
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Which principle or law of geology states that in a sequence of undeformed sedimentary rocks, each bed is older than the one above |
law of superposition |
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The fact that sedimentary rocks are almost always deposited in a horizontal position reflects which law or principle of geology? |
original horizontality |
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original horizontality |
Layers of sediment that are generally deposited in a horizontal or nearly horizontal position. |
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Conformable layers |
Rock layers that were deposited without interruption. |
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While working in the field, you encounter an outcrop in which sandstone, shale, and limestone have been intruded by a basaltic dike. You know that the basaltic dike is younger than the sedimentary rock by applying which law or principle? |
the principle of Crosscutting relationships |
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In the field you encounter a sequence of sedimentary rocks that has a dike running through them. A normal fault crosses the entire sequence, cutting off part of the dike near the surface. Which scenario best describes your observations? (All scenarios list events from oldest to youngest.) |
The relative ages of the sequence are as follows: sedimentary rocks > dike > normal fault. |
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Angular unconformity |
An unconformity in which the older strata dip at an angle different from that of the younger beds. |
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disconformity |
A type of unconformity in which the beds above and below are parallel. |
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Nonconformity |
An unconformity in which older metamorphic or intrusive igneous rocks are overlain by younger sedimentary strata. |
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What term describes an erosional surface bounded above by flat-lying sedimentary rocks and below by igneous or metamorphic rocks? |
nonconformity |
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Any rock fragments included within another rock must be older than the rock in which they are included. (For example, if eroded fragments of one rock layer become part of another sedimentary rock layer, the rock with the included fragments must be younger than the fragments themselves.) |
Inclusions |
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Inclusions |
A piece of one rock unit that is contained within another. Inclusions are used in relative dating. The rock mass adjacent to the one containing the inclusion must have been there first in order to provide the fragment. |
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Numerical date |
The number of years that have passed since an event occurred. (More specific dating) |
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isotopes |
Varieties of the same element that have different mass numbers; their nuclei contain the same number of protons but different numbers of neutrons. |
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radioactive decay |
The spontaneous decay of certain unstable atomic nuclei. |
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alpha particle |
a particle emitted from an atomic nucleus during radioactive decay, which is positively charged and has two neutrons and two proton |
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Name the three products of radioactive decay |
electron capture, beta particle and alpha particle; |
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beta particle |
a fast-moving electron emitted by radioactive decay of substances
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When a beta particle is emitted what occurs |
Neutron becomes a Proton |
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For each beta particle emitted how does that effect the mass number |
no change at all |
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For each beta particle emitted how does that effect the atomic number |
One greater |
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electron capture |
a mode of radioactive decay in which an orbital electron is captured by the nucleus. Then the captured electron combines with a proton to form a neutron Atomic number: 1 more / Atomic mass: no change |
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When an electron is captured by a nucleus how is the mass number effected |
No change |
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When an electron is captured by a nucleus how is the atomic number effected |
One fewer |
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half life |
the time required for one-half of the atoms of a radioactive substance to decay |
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How is the atomic number of an atom determined? |
counting the number of protons |
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After four half-lives of decay, what is the ratio of radioactive parent isotope to stable daughter isotope? |
1/15 |
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A radioactive element undergoes decay via the loss of two alpha particles to form a stable daughter isotope. Following the decay, what would the atomic number of this newly created stable isotope be? |
The atomic number of the daughter isotope would be four units less than the original parent isotope. |
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What happens to isotopes during radioactive decay? |
Parent isotopes turn into daughter isotopes |
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What is the scientific definition of half-life? |
the amount of time over which the number of parent isotopes decreases by half |
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Two containers hold the same radioactive isotope. Container A contains 1000 atoms, and container B contains 500 atoms. Which has a greater rate of decay |
Container A (The rate of decay of atoms in container A is greater than the rate of decay of atoms in container B.) |
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A container holds 100 atoms of an isotope. This isotope has a half-life of 1.5 months. How many total atoms will be in the container after 3 months? |
100 atoms (Atoms of radioactive isotopes turn into atoms of other isotopes.) |
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A container holds 100 atoms of an isotope. This isotope has a half-life of 1.5 months. How many atoms of the radioactive isotope will be in the container after 3 months? |
25 radioactive isotopes |
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A rock sample contains 75 atoms of a parent isotope and 25 atoms of a daughter isotope. The half-life of the parent isotope is 100 years. How old is this rock? |
50 years |
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If one half-life has lapsed, what is the radioactive parent to stable daughter isotope ratio? |
50:50 (The answer is true for the breakdown of all radioactive isotopes.) |
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Precambrian |
all geologic time before the Phanerozoic eon (the current eon we live in) |
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epochs |
a group of the geologic time scale, that is a subdivision group of a period |
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a subdivision of eon is a what |
a era |
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The Phanerozoic eon began how long ago |
542 million years ago |
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what era do we live in |
cenozoic era |
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Name the 4 types of eons |
Phanerozoic, Hadean, Proterozoic, and the archean eon |
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the correct sequence from oldest to most recent or current eras within the phanerozoic eon on the Geologic Time Scale? |
Paleozoic, Mesozoic, Cenozoic |
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Which eon translates to “visible life” from the Greek? |
Phanerozoic |
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Which is the shortest interval of geologic time? |
epochs |
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The subdivisions of the Geologic Time Scale were based on which criteria or characteristics? |
types of fossils within the units |
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Which event is generally used to indicate the beginning of the Phanerozoic eon? |
widespread occurrence of hard parts |
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Carbonization |
Fine sediment encases plant remains, leaving behind an organic residue |
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A worm burrow is an example of which type of fossilization? |
Trace Fossil |
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Lateral continuity (principle of) |
A principle which states that sedimentary beds originate as continuous layers that extend in all directions until they grade into a different type of sediment or thin out at the edge of a sedimentary basin. |
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Geologic Time Scale |
The division of Earth history into blocks of time—eons, eras, periods, and epochs. The time scale was created using relative dating principles. |
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Numerical Date |
The number of years that have passed since an event occurred. |
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Who invented the principle of superposition |
Nicolas Steno, a Danish anatomist, geologist and priest |
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Principle of original horizontality |
A principle by which layers of sediment are generally deposited in a horizontal or nearly horizontal position. |
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If we observe rock layers that are flat it means what |
they have not been disturbed and still have their original horizonality |
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Principle of lateral continuity |
A principle which states that sedimentary beds originate as continuous layers that extend in all directions until they grade into a different type of sediment or thin out at the edge of a sedimentary basin. |
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correlation |
The process of establishing the equivalence of rocks of similar age in different areas. |
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Principle of cross-cutting relationships |
states that geologic features that cut across rocks must form after the rocks they cut through |
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Inclusions |
Fragments of one rock unit that have been enclosed within another |
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xenoliths |
An inclusion of unmelted country rock in an igneous pluton. |
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What is significance of an unconformity |
It represents a long period during which deposition ceased, and then erosion removed previously formed rocks, and then the deposition resumed |
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The scientific study of fossils is called |
paleontology |
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permineralization |
a process of fossilization in which mineral deposits form internal casts of organisms. Carried by water, these minerals fill the spaces within organic tissue |
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Name 5 ways that an animal or a plant can be preserved as a Fossils |
Permineralization, Molds or casts, carbonization or impressions, amber, and trace fossils |
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How is a mold created |
When a shell or other structure is buried in sediment and then dissolved by underground water a mold is formed |
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carbonization |
It occurs when fine sediment encases the remains of an organism. As time passes pressure squeezes out the liquid and gaseous components and leaves behind a thin residue of carbon |
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Amber |
the hardened resin of ancient trees which often contains fossilized insects |
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What conditions favor the preservation of an organism of a fossil |
Ether rapid burial or the possession of hard parts |
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List three examples of trace fossils |
Tracks, burrows, Coprolite (fossilized poo) |
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What is the goal of correlation |
To develop a geologic time scale that is applicable to the entire earth |
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Principle of fossil succession |
The definite and determinable order in which fossil organisms occur. Fossil succession enables us to identify many time periods of rocks by their fossil content. Therefore any time period can be recognized by its fossil content |
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Index Fossils |
Fossils that are widespread geographically and are limited to a short span of geologic time. So their presence provides an important method of matching rocks of the same age |
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Fossil assemblage |
The overlapping ranges of a group of fossils (assemblage) collected from a layer. By examining such an assemblage, the age of the sedimentary layer can be established. |
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Other than being important time indicators how else are fossils useful to geologists |
Fossils are good environmental indicators; showing where the fossils once lived |
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A neutron is actually a proton and an ________ combined |
electron |
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uranium has how many isotopes |
three |
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parent |
An unstable radioactive isotope |
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daughter products |
The isotopes resulting from the decay of the parent |
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earth's oldest rock |
4.28 billion years old |
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Why is radiometric dating a reliable method for determining numerical dates |
because the rates of decay for many isotopes have been precisely measured and do no vary under the physical conditions that exist in Earth's outer layers |
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radiocarbon dating |
Dating of events from the very recent geologic past (the past few tens of thousands of years) based on the fact that the radioactive isotope of carbon is produced continuously in the atmosphere. |
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radiocarbon dating is only useful in dating |
organic materials such as wood, charcoal, bones, flesh, and cloth |
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Name the basic structure of the geologic time scale from largest units of time to smallest |
Eons, Eras, Periods, and Epochs |
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How many periods does the paleozoic era contain |
7 periods |
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How many periods does the mesozoic era contain |
3 periods |
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How many periods does the cenozoic era contain |
3 periods |
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Epochs from later times are simply termed.. |
Early, middle, and late |
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The archean and proterozoic eons are often referred to as the |
Precambrian |
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The earliest interval of earth history (eon); before the oldest known rocks |
Hadean (termed from the Greek god of the underworld, Hades) |
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Why is -zoic part of so many names on the geologic time scale |
because -zoic stands for life |
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How do geologist date sedimentary strata |
By examining their relationship to igneous rock |
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Why it is often difficult to assign a reliable numerical date to a sample of sedimentary rock |
because radiometric dating often is useless to sedimentary rock so geologist have to rely on relative dating |