(See related pages)
Below you will find key words and concepts that you should remember from this chapter.
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| angular unconformity | An unconformity in which younger strata overlie an erosion surface on tilted or folded layered rock. (See page(s) 198) |
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| Archean Eon | The oldest eon of Earth’s history. (See page(s) 210) |
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| Cenozoic Era | The most recent of the eras; followed the Mesozoic Era. (See page(s) 203) |
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| contacts | Boundary surface between two different rock types or ages of rocks. (See page(s) 193) |
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| correlation | In geology, correlation usually means determining time equivalency of rock units. Rock units may be correlated within a region, a continent, and even between continents. (See page(s) 199) |
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| cross-cutting relationship | A principle or law stating that a disrupted pattern is older than the cause of disruption. (See page(s) 194) |
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| disconformity | A surface that represents missing rock strata but beds above and below that surface are parallel to one another. (See page(s) 198) |
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| eon | The largest unit of geological time. (See page(s) 210) |
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| epoch | Each period of the standard geologic time scale is divided into epochs (e.g., Pleistocene Epoch of the Quaternary Period). (See page(s) 203) |
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| era | Major subdivision of the standard geologic time scale (e.g., Mesozoic Era). (See page(s) 203) |
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| faunal succession | A principle or law stating that fossil species succeed one another in a definite and recognizable order; in general, fossils in progressively older rock show increasingly greater differences from species living at present. (See page(s) 201) |
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| formation | A body of rock of considerable thickness that has a recognizable unity or similarity making it distinguishable from adjacent rock units. Usually composed of one bed or several beds of sedimentary rock, although the term is also applied to units of metamorphic and igneous rock. A convenient unit for mapping, describing, or interpreting the geology of a region. (See page(s) 193) |
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| fossil assemblage | Various different species of fossils in a rock. (See page(s) 202) |
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| half-life | The time it takes for a given amount of a radioactive isotope to be reduced by one-half. (See page(s) 207) |
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| inclusion | A fragment of rock that is distinct from the body of igneous rock in which it is enclosed. (See page(s) 198) |
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| index fossil | A fossil from a very short-lived species known to have existed during a specific period of geologic time. (See page(s) 202) |
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| isotope | Atoms (of the same element) that have different numbers of neutrons but the same number of protons. (See page(s) 205) |
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| isotopic dating | Determining the age of a rock or mineral through its radioactive elements and decay products (previously and somewhat inaccurately called radiometric or radioactive dating). (See page(s) 205) |
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| lateral continuity | Principle that states that an original sedimentary layer extends laterally until it tapers or thins at its edges. (See page(s) 194) |
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| Mesozoic Era | The era that followed the Paleozoic Era and preceded the Cenozoic Era. (See page(s) 203) |
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| nonconformity | An unconformity in which an erosion surface on plutonic or metamorphic rock has been covered by younger sedimentary or volcanic rock. (See page(s) 199) |
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| numerical (or absolute) age | Age given in years or some other unit of time. (See page(s) 192) |
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| original horizontality | The deposition of most water-laid sediment in horizontal or near-horizontal layers that are essentially parallel to Earth’s surface. (See page(s) 194) |
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| Paleozoic Era | The era that followed the Precambrian and began with the appearance of complex life, as indicated by fossils. (See page(s) 203) |
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| period | Each era of the standard geologic time scale is subdivided into periods (e.g., the Cretaceous Period). (See page(s) 203) |
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| Phanerozoic Eon | Eon of geologic time. Includes all time following the Precambrian. (See page(s) 210) |
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| physical continuity | Being able to physically follow a rock unit between two places. (See page(s) 199) |
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| Pleistocene Epoch | An epoch of the Quaternary Period characterized by several glacial ages. (See page(s) 203) |
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| Precambrian | The vast amount of time that preceded the Paleozoic Era. (See page(s) 203) |
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| Proterozoic Eon | Eon of Precambrian time. (See page(s) 210) |
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| Quaternary Period | The youngest geologic period; includes the present time. (See page(s) 203) |
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| radioactive decay | The spontaneous nuclear disintegration of certain isotopes. (See page(s) 205) |
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| Recent (Holocene) Epoch | The present epoch of the Quaternary Period. (See page(s) 203) |
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| relative time | The sequence in which events took place (not measured in time units). (See page(s) 193) |
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| standard geologic time scale | A worldwide relative scale of geologic time divisions. (See page(s) 203) |
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| superposition | A principle or law stating that within a sequence of undisturbed sedimentary rocks, the oldest layers are on the bottom, the youngest on the top. (See page(s) 194) |
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| unconformity | A surface that represents a break in the geologic record, with the rock unit immediately above it being considerably younger than the rock beneath. (See page(s) 198) |
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| uniformitarianism | Principle that geologic processes operating at present are the same processes that operated in the past. The principle is stated more succinctly as “The present is the key to the past.” Also, see actualism. (See page(s) 192) |
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| actualism | a scientific philosophy suggesting that the same processes and natural laws we can observe or infer from observation today are those that operated in the geologic past. (See page(s) 192) |
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| Prearchean (Hadean) Eon | the first (earliest) subdivision of the Precambrian interval, extending from 4.55 to 4.00 billion years ago. (See page(s) 210) |