The absolute age of a geologic phenomenon is its age in Earthyears. Compare with relative age.
An area of stratigraphy involving the study of fossilized plants and animals in order to establish dates for and correlations between stratigraphic layers.
A subdiscipline of stratigraphy devoted to studying the relative ages of rocks. Compare with geochronometry.
A method of establishing age relationships between various rock strata. There are two basic types of correlation: physical correlation, which requires comparison of the physical characteristics of the strata, and fossil correlation, the comparison of fossil types.
Any effort directed toward finding the age of a particular item or phenomenon. Methods of geologic dating are either relative (i.e., comparative and usually based on rock strata) or absolute. The latter, based on such methods as the study of radioactive isotopes, usually is given in terms of actual years or millions of years.
The longest phase of geologic time, equivalent to an eonothem in the stratigraphic time scale. Earth's history has consisted of four eons, the Hadean or Priscoan, Archaean, Proterozoic, and Phanerozoic. The next-smallest subdivision of geologic time is the era.
The fourth-longest phase of geologic time, shorter than an era and longer than an age and a chron. An epoch is equivalent to a series in the stratigraphictime scale. The current epoch is the Holocene, which began about 0.01 Ma (10,000 years) ago.
The second-longest phase of geologic time, after an eon, and equivalent to an era them in the stratigraphic time scale. The current eon, the Phanerozoic, has had three eras, the Paleozoic, Mesozoic, and Cenozoic, which is the current era. The next-smallest subdivision of geologic time is the period.
The movement of soil and rock due to forces produced by water, wind, glaciers, gravity, and other influences.
An abbreviation meaning "giga-years" or "billion years." The age of Earth is about 4.6 Ga.
An area of stratigraphy devoted to determining absolute dates and time intervals. Compare with chronostratigraphy.
A map showing the rocks beneath Earth's surface, including their distribution according to type as well as their ages, relationships, and structural features.
The vast stretch of time over which Earth's geologic development has occurred. This span (about 4.6 billion years) dwarfs the history of human existence, which is only about two million years. Much smaller still is the span of human civilization, only about 5,500 years.
The study of Earth's physical history. Historical geology is one of two principal branches of geology, the other being physical geology.
Atoms that have an equal number of protons, and hence are of the same element, but differ in their number of neutrons. This results in a difference ofmass. An isotope may be either stable or radioactive.
The principle that all samples of any given fossil species were deposited on Earth, regardless of location, at more or less the same time. This makes it possible to correlate widely separated strata.
Theprinciple that strata are deposited in a sequence such that the deeper the layer, the older the rock. This is applicable only or sedimentary rock, as opposed to igneous or metamorphic rock.
An area of stratigraphy devoted to the study and description (but not the dating) of rock layers.
An abbreviation used by earth scientists, meaning "million years" or "megayears." When an event is designatedas, for instance, 160 Ma, it usually means 160 million years ago.
The study of fossilized plants and animals, or flora and fauna.
The third-longest phase of geologic time, after an era; it is equivalent to a system in the stratigraphic time scale. The current eon, the Phanerozoic, has had 11 periods, and the current era, the Cenozoic, has consisted of three periods, of which the most recent is the Quaternary. The next-smallest subdivision of geologic time is the epoch.
A term that refers to the first three of four eons in Earth's history, which lasted from about4,560 Ma to about 545 Ma ago.
A term describing a phenomenon whereby certain materials are subject to a form of decay brought about by the emission of high-energy particles or radiation. Forms of particles or energy include alpha particles (positively charged helium nuclei), beta particles (either electrons or subatomic particles called positrons), or gamma rays, which occupy the highest energy level in the electromagnetic spectrum.
A method of absolute dating using ratios between "parent" isotopes and "daughter" isotopes, which are formed by the radioactive decay of parent isotopes.
The relative age of a geologic phenomenon is its age compared with the ages of other geologic phenomena, particularly the stratigraphic record of rock layers. Compare with absolute age.
Material deposited at or near Earth's surface from a number of sources, most notably preexisting rock.
Rock formed by compression and deposition (i.e., formation of deposits) on the part of other rock and mineral particles. Sedimentary rock is one of the three major types of rock, along with igneous and metamorphic.
The study and interpretation of sediments, including sedimentary processes and formations.
Layers, or beds, of rocks beneath Earth's surface. The singular form is stratum.
The succession of rock strata laid down over the course of time, each of which correlates to specific junctures in Earth's geologic history.
The study of rock layers, or strata, beneath Earth's surface.
An apparent gap in the geologic record, as revealed by observing rock layers or strata.
The breakdown of rocks and minerals at or near the surface of Earth due to physical or chemical processes, or both.