Geologic age: Difference between revisions
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#REDIRECT [[Geologic time scale#Terminology]] |
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A '''geologic age''' is a time period on the [[geologic timescale]] delimited by major [[geology|geologic]] or [[paleontology|paleontologic]] events. A geologic age is a subdivision of a [[geologic era]]. |
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When [[William Smith (geologist)|William Smith]] and [[Sir Charles Lyell]] first recognized that [[rock strata]] represented successive time periods, there was no way to determine what time scale they represented. The age of the [[Earth]] and of the rock strata was the subject of scientific debate for over 100 years as various advances in other sciences continued to place the creation of the Earth further into the past. In the latter part of the 20th century, it became possible to assign relatively firm dates using radioactive dating. In the intervening century and a half, geologists and paleontologists devised two relative time scales. One scale -- termed the [[Geologic Timescale]] -- is used by both sciences. [[Geologist]]s tend to talk in terms of Upper/Late, Lower/Middle and often Middle parts of periods or eras -- e.g. "Upper [[Jurassic]]", "Middle [[Cambrian]]". [[Paleontologist]]s divide the same periods into sometimes regional faunal assemblages. For example, in [[North America]] the Late [[Neoproterozoic]] and Early [[Cambrian]] are grouped into a [[Waucoban]] series that is then subdivided into zones based on [[trilobita|trilobites]]. The same [[Neoproterozoic]] timespan is split into [[Tommotian]], [[Atdabanian]] and [[Botomian]] periods in [[East Asia]] and [[Siberia]]. |
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In 1977 The [[Global Commission on Stratigraphy]] started an effort to define global references ([[GSSP]]s) for geologic periods and faunal stages. |
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Latest revision as of 17:21, 10 September 2021
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