Vocabulary For Ch 18 Of Essentials Of Geology

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Archean eon

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the first eon of Precambrian time. The eon preceding the proterozoic. It extends between 4.5 and 2.5 billion years ago

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angular unconformity

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An unconformity in which the older strata dip at an angle different from that of the younger beds

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Cenozoic era

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A time span on the geologic time scale beginning about 65.5 million years ago following the Mesozoic era

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conformable

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Rock layers that were deposited without interruption

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correlation

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To establish the equivalence of rocks of similar age in different areas. Usually used to date sedimentary rock by using igneous rock as the base for age

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principle of cross-cutting relationships

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A principle of relative dating that says that a rock or fault is younger than any rock (or fault) through which it cuts

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disconformity

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A type of unconformity in which the beds above and below are parallel

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eon

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The largest time unit on the geologic time scale, next in order of magnitude above era

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epoch

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The smallest of the time units on the geologic time scale that is a subdivision of a period

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era

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A division on the the geologic time scale eras are divided into shorter units called periods

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fossil

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The remains or traces of organisms preserved from the geologic past

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principle of fossil succession

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the principle that says that fossil organisms succeed one another in a definite and determinable order, and any time period can be recognized by its fossil content

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geologic time scale

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conglomerate of time periods in the history of the Earth dating back 4.5 billion years ago it is divided as follows;Eons,Eras,Periods,Enoch

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half-life

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the time required for one half of the atoms of a radioactive substance to decay.

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inclusion

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A piece of one rock unit 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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index fossil

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A fossil that is associated with a particular span of geologic time.

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Mesozoic Era

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A time span on the geologic time scale between the paleozoic and cenozoic eras from about 251 million to 65.5 million years ago

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nonconformity

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An unconformity in which older metamorphic or intrusive igneous rocks are overlain by younger sedimentary strata

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numerical date

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Date that specifies the actual number of years that have passed since an event occurred

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principle of original horizontality

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Layers of sediment are generally deposited in a horizontal or nearly horizontal position.

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paleontology

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The systematic study of fossils and the history of life on Earth

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paleozoic era

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A time span on the geologic time scale between the Protozoic and Mesozoic eras from about 542 million to 251 million years ago

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period

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A basic unit of the geologic calendar that is a subdivision of an era. Periods may be divided into smaller units called epochs

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Phanerozoic eon

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That part of geologic time represented by rocks containing abundant fossil evidence. the eon extending from the end of the Proterozoic eon about 540 million years ago to the present

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Precambrian

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All geologic time prior to the Paleozoic era

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protozoic eon

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The eon following Archean and preceeding the Phanerozoic eon. it extends between 2.5 billion and 542 million years ago

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radioactivity

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The spontaneous decay of certain unstable atomic nuclei

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radiocarbon dating

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absolute dating of organic material that uses C14 to test half life it can be used to date events as far back as 75000 years ago

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radiometric dating

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The procedure of calculating the absolute ages of rocks and minerals containing certain radioactive isotopes

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relative dating

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Rocks are placed in their proper sequence or order. Only the chronological order of events is determined

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Law of Superposition

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In any undeformed sequence of sedimentary rocks, each bed is older than the one above and younger than the one below

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unconformity

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A surface that represents a break in the rock record caused by erosion or nondeposition