Geologic Age


Also found in: Acronyms.

geologic age

[¦jē·ə¦läj·ik ′āj]
(geology)
Any great time period in the earth's history marked by special phases of physical conditions or organic development.
A formal geologic unit of time that corresponds to a stage.
An informal geologic time unit that corresponds to any stratigraphic unit.

Geologic Age

 

the age of rocks. A distinction is made between absolute and relative geologic ages. Absolute geologic age is the age of rocks as expressed in absolute time units; it is established on the basis of studying the disintegration of radioactive elements (uranium, thorium, potassium, rubidium, and others) contained within minerals. It is usually estimated in millions of years. The term is employed conditionally, since none of the numbers obtained are “absolute,” and absolute age is often given in the first approximation (with a minimal error of ± 5 percent). Relative geologic age is the age of rocks established on the basis of the positions of strata in a cross section with respect to one another. If the strata are dipping, the lower ones are older, and the upper ones are younger (the sequential law of stratification). Comparison of sedimentary layers from regions that are distant from each other has made possible the creation of a general stratigraphic scale, subdivided into a number of segments (systems), which are characterized by specific complexes of plant and animal remains. By analyzing the fossils found in strata, one can identify the place of deposits on the general scale, that is, determine the relative geologic age.

References in periodicals archive ?
As an early (pre-NCGMP) and therefore deprecated alternative, ESRI incorporated an additional relation in which geologic ages are modeled via a relation consisting of attributes that are hierarchically organized.
Fossil: A remnant or trace of an organism of a past geologic age, such as a skeleton or leaf imprint, embedded and preserved in the earth's crust.
This culture destroys a planet and names a geologic age after itself.
Instead, he was living in some new geologic age, one shaped primarily by people, and he gave this new age the name Anthropocene, the Age of Humans.
Is naming a geologic age after ourselves the ultimate act of hubris?
If multiple impacts formed the line, then they must have identical geologic ages, he argues.
Hint of a "Lost World" beneath the sea, a survivor of long-gone geologic ages, has been hauled up in a trawler's net off the east coast of South Africa: a fish of a kind supposed to have disappeared utterly from the earth 50 million years ago.