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.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

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.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
The dataset included rock types and geologic ages for the uppermost bedrock units across Ohio.
It is of approximately the same geologic age as both the type of I.
Is naming a geologic age after ourselves the ultimate act of hubris?
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.
Brown sandstone is from another geologic age about 15 million years ago.
And strontium isotope ratios in soil vary with the geologic age of the rock below.