Paleontology - Key terms
ABSOLUTE AGE:
The absolute age of a geologic phenomenon is its age in Earthyears. Compare with relative age.
ATMOSPHERE:
In general, an atmosphere is a blanket of gases surrounding a planet. Unless otherwise identified, however, the term refers to the atmosphere of Earth, which consists of nitrogen (78%), oxygen (21%), argon (0.93%), and other substances that include water vapor, carbon dioxide, ozone, and noble gases such as neon, which together comprise 0.07%.
BIOSPHERE:
A combination of all living things on Earth—plants, mammals, birds, reptiles, amphibians, aquatic life, insects, viruses, single-cell organisms, and so on—as well as all formerly living things that have not yet decomposed.
BIOSTRATIGRAPHY:
An area of stratigraphy involving the study of fossilized plants and animals to establish dates for and correlations between stratigraphic layers.
CHRONOSTRATIGRAPHY:
A subdiscipline of stratigraphy devoted to studying the relative ages of rocks. Compare with geochronometry.
CONTINENTAL DRIFT:
The theory that the configuration of Earth's continents was once different than it is today; that some of the individual landmasses of today once were joined in other continental forms; and that these landmasses later separated and moved to their present locations.
CORRELATION:
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.
DATING:
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, typically is given in terms of actual years or millions of years.
EON:
The longest phase of geologic time. 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.
EPOCH:
The fourth-longest phase of geologic time, shorter than an era and longer than an age or a chron. The current epoch is the Holocene, which began about 0.01 Ma (10,000 years) ago.
ERA:
The second-longest phase of geologic time, after an eon. 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.
FOSSIL:
The mineralized remains of any prehistoric life-form, especially those preserved in rock before the end of the lastice age.
FOSSILIZATION:
The process by which a once-living organism becomes a fossil. Generally, fossilization involves mineralization of the organism's hard portions, such as bones, teeth, and shells.
GA:
An abbreviation meaning "gigayears," or "billion years." The age of Earth is about 4.6 Ga.
GEOCHRONOMETRY:
An area of stratigraphy devoted to determining absolute dates and time intervals. Compare with chronostratigraphy.
GEOLOGIC TIME:
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.
HISTORICAL GEOLOGY:
The study of Earth's physical history. Historical geology is one of two principal branches of geology, the other being physical geology.
INVERTEBRATE:
An animal without an internal skeleton.
ISOTOPES:
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.
LAW OF FAUNAL SUCCESSION:
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.
MA:
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.
MASS EXTINCTION:
A phenomenon in which numerous species cease to exist at or around the same time, usually as the result of a natural calamity.
MINERALIZATION:
A series of changes experienced by a once-living organism during fossilization. In mineralization, minerals in the organism are either replaced or augmented by different minerals, or the hard portions of the organism dissolve completely.
ORGANIC:
At one time, chemists used the term organic only in reference to living things. Now the word is applied to most compounds containing carbon, with the exception of carbonates (which are minerals), and oxides, such as carbon dioxide.
PALEOBOTANY:
An area of paleontology involving the study of past plant life.
PALEOECOLOGY:
An area of paleontology devoted to studying the relationship between prehistoric plants and animals and their environments.
PALEONTOLOGY:
The study of life-forms from the distant past, primarily as revealed through the fossilized remains of plants and animals.
PALEOZOOLOGY:
An area of paleontology devoted to the study of prehistoric animal life.
PERIOD:
The third-longest phase of geologic time, after an era. 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.
PRECAMBRIAN TIME:
A term that refers to the first three of four eons in Earth's history, which lasted from about 4,560 to about 545 Ma ago.
RADIOACTIVITY:
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.
RADIOMETRIC DATING:
A method of absolute dating using ratios between "parent" isotopes and "daughter" isotopes, which are formed by the radioactive decay of parent isotopes. Radiometric dating also may involve ratios between radioactive isotopes and stable isotopes.
RELATIVE AGE:
The relative age of a geologic phenomenon is its age compared with other geologic phenomena, particularly the stratigraphic record of rock layers. Compare with absolute age.
SEDIMENT:
Material deposited at or near Earth's surface from a number of sources, most notably preexisting rock.
SEDIMENTARY 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.
SEDIMENTOLOGY:
The study and interpretation of sediments, including sedimentary processes and formations.
STRATA:
Layers, or beds, of rocks beneath Earth's surface. The singular form is stratum.
STRATIGRAPHY:
The study of rock layers, or strata, beneath Earth's surface.
VERTEBRATE:
An animal with an internal skeleton.