Glossary of Terms

Choose the first letter of the the term you're interested in:
| A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z |

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Acanthodians: A primitive group of Silurian to Permian jawed bony fishes, bearing bony spines in front of all but their caudal fins.
Albian: European stage of the uppermost Lower Cretaceous, spanning the time between 107 and 95 million years ago.
Algae: Photosynthetic, almost exclusively aquatic, nonvascular plants that range in size from simple unicellular forms to giant kelps several feet long. They have extremely varied life cycles and first appeared in the Precambrian.
Ammonite: A coiled, chambered fossil shell of a cephalopod mollusk of the extinct order Ammonoidea.
Amoeba: A microscopic, one-celled animal consisting of a naked mass of protoplasm.
Aperture: A relatively large opening on the last-formed chamber of a foraminiferal shell.
Aptian: European stage of the Lower Cretaceous, spanning the time between 114 and 107 million years ago.
Archaean: The middle era of Precambrian time, spanning the period between 3.8 and 2.5 billion years ago. Life arose on Earth during the early Archaean, as indicated by the appearance of fossil bacteria in rocks thought to be about 3.5 billion years old. Its name means "ancient."

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Barremian: European stage of the Lower Cretaceous, spanning the time between 118 and 114 million years ago.
Benthic: Used to describe aquatic organisms that are bottom dwelling.
Berriasian: European stage of the lowermost Lower Cretaceous, spanning the time between 135 and 131 million years ago.
Bioluminescence: The production of light by living organisms.
Biostratigraphy: The branch of geology concerned with the separation and differentiation of rock units by means of the study of the fossils they contain.
Bivalve: A mollusk having two shells hinged together, as the oyster, clam, or mussel; or any animal with two halves to its shell such as an ostracode or brachiopod.
Bony Fishes: Fish of the class Osteichthyes, characterized by a skeleton composed of bone in addition to cartilage, gill covers, and an air bladder.

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Caecilians: Wormlike, almost blind, tropical amphibians of the order Apoda.
Calcareous: Of, containing, or like calcite (calcium carbonate).
Calcareous Nannofossils: Fossil remains of calcareous nannoplankton.
Calcareous Nannoplankton: Protists that normally produce coccoliths during some phase in their life cycle.
Calcite: A common rock-forming mineral: CaCO₃. Calcite can be white, colorless, or pale shades of gray, yellow, and blue. It readily effervesces (bubbles) in hydrochloric acid and is the principal component of limestone.
Cambrian: The earliest period of the Paleozoic era, spanning the time between 544 and 505 million years ago. It is named after Cambria, the Roman name for Wales, where rocks of this age were first studied.
Campanian: European stage of the Upper Cretaceous, spanning the time between 84 and 72 million years ago.
Carboniferous: A period of time in the Paleozoic era that includes the Pennsylvanian and Mississippian periods and extended from 360 to 286 million years ago.
Cartilaginous Fishes: Fish having a skeleton composed mostly of cartilage, as sharks and rays. Cartilage is gristle or a firm, elastic, flexible type of connective tissue.
Cenomanian: European stage of the lowermost Upper Cretaceous, spanning the time between 95 and 91 million years ago.
Cenozoic: An era of geologic time from the beginning of the Tertiary period (65 million years ago) to the present. Its name is from Greek and means "new life."
Coccoliths: Microscopic structures of varying shape and size that are made of calcite, are secreted by calcareous nannoplankton, and are found in marine deposits from the Triassic period to the Recent. Coccoliths range in size from one to thirty-five micrometers in size.
Coniacian: European stage of the Upper Cretaceous, spanning the time between 90 and 88 million years ago.
Core: A cylindrical section of rock, usually 2-4 inches in diameter and up to several feet long, that is the result of coring into the earth. Individual cores are brought to the surface for geologic examination and/or laboratory analysis.
Cretaceous: The final period of the Mesozoic era, spanning the time between 145 and 65 million years ago. The name is derived from the Latin word for chalk ("creta") and was first applied to extensive deposits of this age that form white cliffs along the English Channel between Great Britain and France.

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Devonian: A period of the Paleozoic era, spanning the time between 410 and 360 million years ago. It is named after Devonshire, England, where rocks of this age were first studied.
Diagenesis: All chemical, physical, and biological modifications undergone by a sediment after its initial deposition.
Dinocyst: A resting stage or reproductive stage in the life cycle of a dinoflagellate.
Dinoflagellate: Small organisms with both plant-like and animal-like characteristics, usually classified as algae (plants). They take their name from their twirling motion and their whip-like flagella.

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Ecology: A branch of biology dealing with the relations between living plants and animals and their environment.
Ecosystem: A part of ecology consisting of the environment, its living parts, and the nonliving factors that affect it.
Eocene: An epoch of the lower Tertiary period, spanning the time between 55.5 and 33.7 million years ago. Its name is from the Greek words "eos" (dawn) and "ceno" (new).

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Fauna: Animals of a given region or period of geologic time.
Flora: Plants of a given region or period of geologic time.
Foraminifer: Protozoans that belong to the subclass Sarcodina, order Foraminifera, that have a test of one to many chambers composed of secreted calcite or agglutinated particles.
Fossil: Fossils are the recognizable remains, such as bones, shells, or leaves, or other evidence, such as tracks, burrows, or impressions, of past life on Earth.
Fossilization: All the processes that involve the burial of a plant or animal in sediment and the eventual preservation of all, part, or a trace of it.

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Geochemistry: The science that deals with chemical changes in and composition of the earth's crust.
Geologic Time: The period of time extending from the formation of the earth to the present.
Geologic Time Scale: An arbitrary chronologic sequence of geologic events, used as a measure of the age of any part of geologic time, usually presented in the form of a chart showing the names of the various rock-stratigraphic, time-stratigraphic, or geologic-time units.
Geology: The study of the planet Earth - the materials of which it is made, the processes that act on these materials, the products formed, and the history of the planet and its life forms since its origin

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Hadean: The earliest subdivision of the Precambrian, spanning the time between the formation of the Earth, about 4.5 billion years ago, and the start of the Archaean era, 3.8 billion years ago. This interval predates the period of true geologic time since no rocks of this age are known on Earth, with the exception of a few meteorites.
Hauterivian: European stage of the Lower Cretaceous, spanning the time between 122 and 118 million years ago.
Holocene: An epoch of the Quaternary period, spanning the time from the end of the Pleistocene (8,000 years ago) to the present. It is named after the Greek words "holos" (entire) and "ceno" (new).
Hydrogeology: The science that deals with subsurface waters and geologic aspects of surface waters.

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Isotopic Dating: Radiometric dating; all methods of age determination based on nuclear decay of naturally occurring radioactive isotopes. Age in years for geologic materials are calculated by measuring the presence of a short-life radioactive element, e.g. carbon-14, or by measuring the presence of a long-life radioactive element plus its decay product, e.g. potassium-40/argon-40. See the USGS publication "Geologic Time" for more details.

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Jurassic: The middle period of the Mesozoic era, spanning the time between 213 and 145 million years ago. It is named after the Jura Mountains between France and Switzerland, where rocks of this age were first studied.

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Lithologic Unit: Lithostratigraphic unit; a body of rock that is consistently dominated by a certain lithology or similar color, mineralogic composition, and grain size. It may be igneous, sedimentary, or metamorphic and may or may not be consolidated.

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Maastrichtian: European stage of the Upper Cretaceous, spanning the time between 72 and 66 million years ago.
Macrofossil: A fossil that is large enough to be studied without a microscope.
Mesozoic: An era of geologic time between the Paleozoic and the Cenozoic, spanning the time between 248 and 65 million years ago. The word Mesozoic is from Greek and means "middle life."
Microfossil: A fossil so small that it must be studied with a microscope.
Micrometer: A unit of measure. There are one million micrometers in one meter.
Miocene: A epoch of the upper Tertiary period, spanning the time between 23.8 and 5.3 million years ago. It is named after the Greek words "meion" (less) and "ceno" (new).
Mississippian: A period of the Paleozoic era, spanning the time between 360 and 325 million years ago. It is named after the Mississippi River valley, which contains good exposures of rocks of this age.
Morphology: The study of form and structure of animals and plants and their fossil remains.

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Nektonic: Used to describe aquatic organisms that swim.
Notochord: A rodlike cord of cells in lower chordates that forms the main lengthwise support structure of the body.

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Oligocene: An epoch of the early Tertiary period, spanning the time between 33.7 and 23.8 million years ago. It is named after the Greek words "oligos" (little, few) and "ceno" (new).
Ordovician: The second earliest period of the Paleozoic era, spanning the time between 505 and 440 million years ago. It is named after a Celtic tribe called the Ordovices.
Ostracoderms: Primitive jawless fishes, covered by bony armor, that lived in the Cambrian through Devonian periods.

- P -

Paleobathymetry: The study of ocean depths and topography of the ocean floor in the geologic past.
Paleobiogeography: The branch of paleontology that deals with the geographic distribution of plants and animals in past geologic time, especially with regard to ecology, climate, and evolution.
Paleoceanography: The study of oceans in the geologic past, including its physical, chemical, biologic, and geologic aspects.
Paleocene: Earliest epoch of the Tertiary period, spanning the time between 65 and 55.5 million years ago. It is named after the Greek words "palaois" (old) and "ceno" (new).
Paleoclimate: The climate of a given period of time in the geologic past.
Paleoecology: The study of the relationships between ancient plants and animals and their environments.
Paleoenvironment: Environment in the geologic past.
Paleontologist: Scientists who study fossils.
Paleontology: The study of life in past geologic time.
Paleozoic: An era of geologic time, from the end of the Precambrian to the beginning of the Mesozoic, spanning the time between 544 and 248 million years ago. The word Paleozoic is from Greek and means "old life."
Pelagic: Referring to open water marine habitats free of direct influence of the shore or ocean bottom. Pelagic organisms are generally free-swimming (nektonic) or floating (planktonic).
Pennsylvanian: A period of the Paleozoic era, spanning the time between 325 and 286 million years ago. It is named after the state of Pennsylvania where rocks of this age are widespread.
Permian: The final period of the Paleozoic era, spanning the time between 286 and 248 million years ago. It is named after the province of Perm, Russia, where rocks of this age were first studied.
Phanerozoic: The period of time, also known as an eon, between the end of the Precambrian and today, The Phanerozoic begins with the start of the Cambrian period, 544 million years ago. It encompasses the period of abundant, complex life on the Earth.
Placoderms: A peculiar group of primitive armored jawed fish, found almost exclusively in rocks from the Devonian Period.
Plankton: Aquatic organisms that drift, or swim weakly.
Planktonic: Used to describe aquatic organisms that float.
Pleistocene: An epoch of the Quaternary period, spanning the time between 1.8 million years ago and the beginning of the Holocene at 8,000 years ago. It is named after the Greek words "pleistos" (most) and "ceno" (new).
Pliocene: Final epoch of the Tertiary period, spanning the time between 5.3 and 1.8 million years ago. It is named after the Greek words "pleion" (more) and "ceno" (new).
Precambrian: All geologic time before the beginning of the Paleozoic era. This includes about 90% of all geologic time and spans the time from the beginning of the earth, about 4.5 billion years ago, to 544 million years ago. Its name means "before Cambrian."
Proterozoic: The final era of the Precambrian, spanning the time between 2.5 billion and 544 million years ago. Fossils of both primitive single celled and more advanced multicellular organisms begin to appear in abundance in rocks from this era. Its name means "early life."
Protist: An organism that belongs to the kingdom Protista, which includes forms with both plant and animal affinities, i.e., protozoans, bacteria, and some algae, fungi, and viruses.

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Quaternary: The second period of the Cenozoic era, spanning the time between 1.8 million years ago and the present. It contains two epochs: the Pleistocene and the Holocene. It is named after the Latin word "quatern" (four at a time).

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Rhizopod: A protozoan of the class Rhizopoda that has pseudopodia.
Rudist: An extinct bivalve mollusk from the Jurassic and Cretaceous that had two different sized and shaped shells; they usually were attached to the substrate and were either solitary or in reeflike masses.

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Santonian: European stage of the Upper Cretaceous, spanning the time between 88 and 84 million years ago.
Scanning Electron Microscope (SEM): A microscope in which a finely focused beam of electrons is scanned across a specimen, and the electron intensity variations are used to construct an image of the specimen. This type of microscope is ideal for magnifications from 200 to 35,000.
Sediment: Solid unconsolidated rock and mineral fragments that come from the weathering of rocks and are transported by water, air, or ice and form layers on the Earth's surface. Sediments can also result from chemical precipitation or secretion by organisms.
Sedimentary Rock: A rock that is the result of consolidation of sediments.
Silurian: A period of the Paleozoic, spanning the time between 440 and 410 million years ago. It is named after a Celtic tribe called the Silures.
Stratigraphy: The branch of geology concerned with the formation, composition, ordering in time, and arrangement in space of sedimentary rocks.
Subtropical: Bordering on the tropics or nearly tropical.

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Taxonomy: The science dealing with the identification, naming, and classification of plants and animals.
Terrestrial: Referring to land habitats in distinction from water (aquatic) habitats.
Tertiary: The first period of the Cenozoic era (after the Mesozoic era and before the Quaternary period), spanning the time between 65 and 1.8 million years ago.
Triassic: The earliest period of the Mesozoic era, spanning the time between 248 and 213 million years ago. The name Triassic refers to the threefold division of rocks of this age in Germany.
Tropical: Referring to climatic conditions like those found in the region on the earth today between the tropic of Cancer and the tropic of Capricorn; it includes high temperature and humidity and abundant rainfall.
Turonian: European stage of the Upper Cretaceous, spanning the time between 91 and 90 million years ago.

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- V -

Valanginian: European stage of the Lower Cretaceous, spanning the time between 131 and 122 million years ago.

Vendian: The latest period of the Proterozoic era, spanning the time between 650 and 544 million years ago. Sometimes referred to as the Ediacaran period, the Vendian is distinguished by fossils representing a characteristic collection of complex soft-bodied organisms found at several localities around the world.

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