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
AA: An Hawaiian word for a mafic lava flow with an especially rough, jagged surface.
ABALATION: The total amount of ice a glacier loses annually. See also ACCUMULATION.
ABSOLUTE DATING: The numerical age of a feature, expressed in years, or the year of occurrence of an event.
ABSOLUTE MAGNITUDE: A measure of a star's brightness, equal to its apparent magnitude if the star were 10 parsecs from the Sun. Absolute magnitude is thus independent of distance from the Solar System.
ABYSSAL PLAIN: The region of approximately flat ocean floor that extends from the mid-oceanic ridges to the continental rises. It comprises most of the ocean floor.
ACID: A reactive solution containing an excess of hydrogen ions. See also BASE.
ACRE: A unit of land measure equal to 160 square rods or 43,560 square feet (0.405 hectare).
ACCUMULATION: The amount of snow added to a glacier annually. See also ABALATION.
ADAPTATION: The evolution of new traits through natural selection that increase fitness to the local environment.
ADAPTIVE LANDSCAPE: A pictorial representation of the relationship between fitness and genotype, or between fitness and the genetic composition of a population; developed by Sewall Wright (need reference).
ADSORPTION: The process by which atoms, molecules, or ions are attracted to and retained on a surface.
ADVECTION: Horizontal transport of material, such as air or water vapor, by moving air or wind. See also CONVECTION.
AEROBIC: (a) An environment containing molecular oxygen (O2). (b) Growing only in the presence of molecular oxygen (O2), as aerobic organisms. (c) Occurring only in the presence of molecular O2. See also anaerobic.
AIR MASS: A large body of air overlying a region of Earth's surface and exhibiting broadly similar characteristics throughout, especially in regard to surface temperature and moisture. See also SOURCE REGION.
ALBEDO: The "reflectivity" of a surface. More strictly, the ratio of [the amount of light reflected from a surface] to [the amount incident upon the surface], expressed either as a percentage or a decimal fraction. An albedo of one (a = 1.0) indicates a perfect reflector; an albedo of zero (a = 0.0) indicates a perfect absorber (BLACKBODY). The albedo of new snow is around 0.9; that of water is around 0.1, but is strongly dependent on the angle of the incident radiation.
ALGAE: See also CRUSTOE ALGAE, TURF ALGAE.
ALLELE: A form or realization of a gene.
ALLELOPATHY: A competitive device involving the production of chemical to harm others.
ALLUVIAL FAN: An open, fan-shaped deposit of loose rock material at the place where a narrow mountain canyon opens on to a wide, flat plain.
ALLUVIUM: Sediment deposited on land by streams, such as sand, silt, and mud; usually well sorted by particle size and deposited in river beds, flood plains, and lakes.
ALTRUIST: An individual that performs an activity at the apparent sacrifice of its immediate benefit.
AMBER: Fossilized tree sap. Amber is not a mineral because it is amorphous, that is, it has no crystalline structure.
AMINO ACID: The building block for proteins and other polypeptides; composed of an amino acid group and a carboxylic acid group.
AMMONIA: NH3, a compound of hydrogen (H) and nitrogen (N).
AMPHIBOLE: A common rock-forming silicate; a chain silicate mineral that contains a double chain structure. Amphibole is often dark in color and is #6 on the Mohs scale of hardness. It has a variable chemical composition of calcium, iron, magnesium, silicon, oxygen, and many others.
ANAEROBIC: (a)An environment lacking molecular oxygen. (b) Biological processes not requiring oxygen. See also aerobic.
ANGIOSPERM: a flowering plant which produces seeds enclosed in a fleshy fruit.
ANGULAR (ROTATIONAL) MOMENTUM: A measure of the spin momentum of an object. Any spinning body has angular momentum, the amount depending directly on the mass of the object and on the rate of spin. It also depends on how the mass of the object is extended with respect to the center of rotation; the more extended a body, the greater the angular momentum.
ANTARCTIC: Region south of the Antarctic Circle.
ANTARCTIC CIRCLE: See Arctic Circle.
ANTICLINE: A convex, upward fold; an up-thrusting fold or arch of rock strata that bends downward on both sides from its axis. When eroded, the center beds (axis beds) are older than the beds o either side. See also SYNCLINE.
ANTHROPIC PRINCIPLE: The concept that, if life can exist only a limited range of conditions, the world in which we exist must satisfy those conditions, hence there is an observer bias.
ANTICYCLONE: An area wherein the atmospheric pressure is high relative to the surrounding area; a high pressure system producing subsidence and outward flow of air; in the Northern (Southern) Hemisphere, a clockwise (counter-clockwise) flow of air. See also CYCLONE.
APHELION: The point in a planet's orbit when it is farthest from the Sun. (The more general term is apogee.) See also PERIHELION.
APPARENT MAGNITUDE: A measure of a star's observed brightness. Apparent magnitude depends strongly on distance -- a bright star far away may have the same apparent magnitude as a nearby dim star. See also ABSOLUTE MAGNITUDE.
APPARENT PATH: The motion of the CELESTIAL SPHERE as observed from a point on the surface the rotating EARTH; that is, the stars and the SUN rise on the eastern horizon and set on the western horizon.
ARCHEAN: The second eon on the geologic time scale, running from 3.8 Billion to 2.5 Billion years ago. For more detail, see the Geologic Time Scale.
AQUIFER: A rock formation that holds water.
ARCTIC: Region north of the Arctic Circle.
ARCTIC CIRCLE: The southernmost latitude circle in the Northern Hemisphere on which the Sun does not raise for one full day each year. This latitude is given by 90° N - obliquity. See Antarctic Circle.
ARTHROPOD: The phylum of invertebrate animals which includes insects, crustaceans (crabs, barnacles, shrimp), arachnids (spiders, scopions, mites, and ticks), and myriapods (centipedes and millipedes). The over one-million classified species of arthropods are characterized by a segmented body, usually with specialized regions (e.g., head, thorax, and abdomen), and usually hardened, jointed appendages.
(VOLCANIC) ASH: Fine, pyroclastic material, less than 2 mm in size.
ASTEROID: A small rocky and/or metallic body, usually in an orbit laying between the orbits of Mars and Jupiter. It is speculated that these are objects left over from the formation of the Solar System which did not coalesce to form a planet because of continual disturbance by the nearby Jupiter. See The Asteroid Belt for more details.
ASTHENOSPHERE: A zone in the upper mantle where rocks may be melted or partially melted. This zone underlies the lithosphere; it continues downward from the upper mantle to a depth of about 250 kilometers where the mantle material again behaves like a solid. The asthenosphere is thought to be at least partially melted because earthquake waves (S- and P-waves) slow down as they pass through it. The asthenosphere is the layer over which the plates of the lithosphere move.
ASTRONOMY: The study of the science of the position, motion, constitution, history, and destiny of celestial bodies.
ASTRONOMICAL UNIT (AU): 1 AU = mean distance between the Sun and Earth (~1.495 x 108 kilometers); a commonly used scale length for distances in the Solar System.
ASTROPHYSICAL EFFECT:
ATMOSPHERE: The shell of gases enveloping a planet, held in place by the planet's gravitation. More specifically, Earth’s surrounding tenuous blanket of gases, particulates (both solid and liquid), and water (in various phases). Relative to the size of the planet, Earth's atmosphere is a thin film.
ATMOSPHERIC SCIENCE: The scientific discipline focused on the study of Earth's atmosphere. See also ATMOSPHERIC SCIENCE, meteorology, and climatology.
ATOLL: A ring-shaped coral reef, either continuous or broken, surrounding a central lagoon.
ATOM: The fundamental unit of an element; it is the smallest particle of an element that retains the properties of the element and that can take part in a chemical reaction. For each element, an atom consists of a unique (fixed) number of positively charged protons in a central nucleus surrounded by a cloud of an equal number of negatively charged electrons. An atom as a whole is thus electrically neutral. However, atoms may gain or lose electrons to become negative or positive ions, respectively. The nucleus may also contain a variable number of neutrons, giving rise to isotopes of the element. See also ATOMIC MASS and ATOMIC NUMBER.
ATOMIC MASS: The sum of the number of protons and the number of neutrons in the nucleus of an atom. Atoms of chemical element have a fixed atomic number, but can have different atomic masses, denoting different isotopes of that element.
ATOMIC NUMBER: The number of protons in the nucleus of an atom. This number is unique to each element. The symbol Z is often used to denote atomic numbers.
AUREOLE: The zone adjacent to an igneous intrusion that shows the effect of contract metamorphism.
AURORA: Luminous phenomena of the upper atmosphere, appearing in the form of green or red rays, arcs, bands, curtains, and streamers. Normally observed at high latitudes, under some conditions they may be visible in the mid-latitudes. Satellite imagery of the polar regions show aurora to form rings encircling each of Earth's magnetic poles. An aurora is caused by the interaction of particles in Earth's atmosphere with charged particles from the Sun. Because of the incoming particles electrical charge, they spiral in along the magnetic field lines. In the Northern Hemisphere, Aurora Borealis, in the Southern Hemisphere, Aurora Austrailus.
AUTOTROPH: An organism which synthesizes the organic materials it needs from inorganic sources, such as carbon dioxide and nitrates. Green plants are photoautotrophic.
AVALANCHE: A large mass of snow and/or ice (and perhaps also entrained detritus such as soil, rock, and vegetation) moving rapidly downhill under the effect of gravity.
AXIAL PLANE: The plane passing through a series of hinge-lines or axes of a fold.
AXIS: a) In mechanics, the axis of rotation, the line about which a body rotates. b) In geology, a line dividing a fold; the hinge-line of a fold. See also AXIAL PLANE.
BACKWASH: The water returning to the sea after a wave has broken on a shore.
BARRIER ISLAND: A significant sand bar extending above sea-level. The Outer Banks of North Carolina are barrier islands.
BAR: In surface hydrology, sand or gravel bar, an accumulation of sand or gravel where the velocity of a stream as decreased.
BARYCENTER: The center of mass of a two-body system. More specifically, it is the point within the Earth around which the planet and the Moon revolve.
BASALT: A fine-grained, extrusive or volcanic, mafic igneous rock, composed mostly of pyroxene and plagioclase, with some olivine and/or amphibole.
BASALTIC MAGMA: See MAFIC MAGMA.
BASALT PLATEAU: A large area built up over time by successive basaltic lava flows; can be thousands of feet thick.
BASIC CYCLE: A tracking of the flow of every bit of element within the Earth system. Normally not used since much of an element is often contained in largely inert reservoirs, often buried deep in the geosphere. Usually attention is focused only on particularly active portions (a geochemical cycle) of a basic cycle.
BASIN: A depressed region with no outlet.
BATHOLITH: A massive, discordant pluton greater than 100 km2 (36 mi2) in area.
BEACH: A shoreline made up of sand and pebbles.
BEACH ENVIRONMENT: The area of an ocean beach between the low and high tide.
BED: The smallest easily recognizable unit in a sequence of rocks or sediments. A bed may be from a few inches to 100 feet thick.
BED LOAD: The sediment moving along the bottom of a stream, neither in solution nor in suspension; the coarsest sediment the stream carries. In essence, this is material at the bottom of the stream that is being dragged along by the flowing water.
BEDDING PLANES: The planes that separate the beds.
BIOGEOCHEMICAL CYCLE: The prefix "bio-" is added to denote those geochemical cycles involving living organisms in one or more processes.
BIOGEOCHEMICAL SEDIMENTARY ROCK: Sedimentary rock that forms from organic sedimentation. See LIMESTONE.
BIOMASS: The dry weight of a living thing. The planetary biomass is the total dry weight of all living material on the planet. See also phytomass and zoomass.
BIOME: A major ecosystem such as temperate grasslands, forests of various types, tundra, and desert.
BIOSPHERE: The thin, roughly spherical shell in the Earth System that is inhabited by living organisms; overlaps the lower atmosphere, the hydrosphere, and the crust.
BIOTA: All living things on the planet.
BIOTITE MICA: A common rock-forming silicate, generally dark in color and ranking #4 on the Mohs scale of hardness. It has a variable chemical composition of calcium, iron, magnesium, silicon, and oxygen, with water in its crystalline structure. See also MICA, MOSCOVITE MICA.
BLACK HOLE: A "collapsed" star whose gravitational field is so strong that no even light can escape.
BLACKBODY RADIATION: A material that absorbs all incident radiation at all wavelengths (ALBEDO = 0.0) appears black and is called a blackbody. Such materials also emit electromagnetic radiation in a predictable manner. Blackbody radiators are the most efficient thermal radiators possible.
BODY WAVE: Seismic waves that travel through the Earth. See also P-WAVE, SURFACE WAVE, S-WAVE.
BOILING TEMPERATURE: The temperature at which a pure substance changes rapidly from liquid to gas, usually with the formation of bubbles within the mass of liquid.
BOND: In chemistry, the binding mechanism between atoms.
BOULDER: A clastic fragment larger than 256 millimeters (~10 inches) in size.
BOTTOMSET BEDS: See DELTA.
BOUNDARY: The line dividing two regions. In practice, often a zone of transition between two regions but because of the zone's width being much, much less than its length, appearing as a sharp demarcation when viewed on a global scale -- atmospheric examples: warm and cold fronts. In other cases, the transition is very gradual, such as for the "top" of the atmosphere, and the drawing of a boundary is purely descriptive.
BOWEN'S REACTION SERIES: An interpretation of the crystallization sequence of minerals in igneous rocks, theorized by N.L. Bowen in 1936.
BRAIDED STREAM: A stream that has split into a tangled network of small streams that split and reunite, winding along a stream channel filled with sediment from times when the water flow is much greater.
BREAKER: A crashing wave close to shore.
BRECCIA: A clastic sedimentary rock composed of angular fragments, most of which are greater than 2 millimeters in size.
BURIAL PRESSURE: See COMPACTION.
CALCITE: A common rock-forming mineral. Calcite ranks #3 on the Mohs scale of hardness. It has a chemical composition of calcium, carbon, and oxygen. See CALCIUM CARBONATE, LIMESTONE.
CALCIUM CARBONATE (CaCO3): The formal chemical name for the mineral calcite. Calcium carbonate is an oxide.
CALDERA: A depression, often roughly circular in shape, caused by the collapse of the central part of a volcano
CALVING: The breaking off of a mass of ice from a glacier or ice sheet into a water body, creating icebergs.
CAMBRIAN: The geological time period extending from 570 to 505 million years ago. Named after the Cambria, the Latin name for a tribe inhabiting the region now known as Wales. For more detail, see the Geologic Time Scale. See also PRE-CAMBRIAN, GEOLOGIC TIME
CANYON: A deep, narrow, steep-sided valley, often with a stream at the bottom.
CARBON: (C) A non-metal from Group IV of the periodic table. It has atomic number 6. For more information, see The Elements.
CARBON DIOXIDE: CO2; made up of one carbon and two oxygen atoms. It makes up most of the atmosphere's of Venus and Mars, but only a very small fraction of Earth's (~0.03 to 0.04%). Carbon dioxide is an important greenhouse gas.
CARBONATE ROCK: See LIMESTONE.
CARBONIC ACID: A weak acid formed by the reaction of water with carbon dioxide in the atmosphere.
CARBONIFEROUS: The European name for the period in the Paleozoic Era extending 360 to 286 Million years ago. This time period is equivalent to the Mississippian and Pennsylvanian in North America.
CELESTIAL SPHERE: An imaginary sphere of infinite radius surround the EARTH and serving as a screen against which all celestial objects are seen. A coordinate system drawn on the celestial sphere (analogous to LATITUDE and LONGITUDE on the Earth) allows precise specification of the location of celestial bodies; see DECLINATION.
CELESTIAL EQUATOR: The projection of the EARTH's equator on the CELESTIAL SPHERE.
CELESTIAL POLES: Points of intersection by extension of the EARTH's axis to the CELESTIAL SPHERE.
CELLULAR SLIME MOLD: Various fungi whose vegetative structures are aggregations of amoeboid cells.
CEMENTATION: The binding together of sedimentary particles.
CENOZOIC: The third and current era of the Phanerozoic eon in geologic time, extending from 65 Million years ago to the present. "New" or "recent life" in Latin. For more detail, see the Geologic Time Scale. It is divided into two periods: Tertiary; and Quaternary.
CENTER OF MASS: The point around which two bodies (two stars, or a star and a planet) revolve. The center of mass lies along a line joining the two centers of gravity, and is closest to the more massive object.
CETACEAN: The order of mammals that is exclusively aquatic. It is includes dolphins and whales.
CFC: See CHLOROFLUOROCARBON.
CHAIN SILICATE: a silicate mineral in which each silicon atom shares two of its four oxygen atoms. See PYROXENE and AMPHIBOLE.
CHALK: A biochemical sedimentary rock mostly composed of the mineral calcite.
CHANGE OF PHASE: Going from one state of matter (solid, liquid, or gas) to another.
CHANNEL: A narrow depression that carries flowing water either continuously or periodically.
CHANNELIZATION: Any of a range of modifications of a stream channel.
CHARACTER DISPLACEMENT: The evolutionary divergence of similar traits among coexisting competitors.
CHEMICAL COMPOSITION: The chemical components of minerals or rocks, generally expressed as elements or oxides.
CHEMICAL COMPOUND: A material containing two or more elements.
CHEMICAL ELEMENT: See The Elements.
CHEMICAL SEDIMENTARY ROCK: Sedimentary rocks that form from precipitation of minerals from a solution. See LIMESTONE.
CHEMICAL WEATHERING: The decomposition of rocks at the Earth's surface by chemical reactions. Chemical weather usually changes the minerals in the weathering rocks.
CHLOROPHYLL: A green pigment found in chloroplasts of many plant cells. This compound absorbs radiant energy from the Sun, i.e., sunlight, and catalyzes photosynthesis.
CHLOROPLASTS: Structures found in the cytoplasm of green plant cells that contain chlorophyll. Chloroplasts are the site of photosynthesis.
CHROMOSOME: The site of genes; linear structure within a cell nucleus providing the location of the DNA.
CHROMOSPHERE: The ~10,000 kilometer thick layer of the Sun's atmosphere, immediately above the photosphere. See also The Sun.
CINDER CONE: A small, steep-sided volcano (usually less than 400 meters tall) made of pryoclastic materials.
CIRQUE: An amphitheater-shaped hollow carved out of the side of a mountain by glacial processes.
CLASS: The classification level immediately following Phylum. The major classes of the phylum Chordata are fish, amphibian, reptile, avian, and mammal.
CLAST: A clastic fragment.
CLASTIC FRAGMENT: A solid rock or mineral fragment produced by weathering.
CLASTIC SEDIMENTARY ROCKS: Rocks formed from clastic fragments.
CLAY-SIZED PARTICLE:
CLEVAGE: The tendency of minerals to break (or "cleave") along a plane which has low resistance due to the pattern of the mineral's crystal structure. Many minerals break in a regular way that produces a smooth plane that reflects light; this property can be used to characterize individual minerals.
CLIMATE: The long-term (decades and more) state of Earth's atmosphere, oceans, and surface. Often expressed in terms of average and extreme conditions for temperature, pressure, moisture content, wind, surface conditions, etc..., and in terms of spatial patterns of these quantities on local, regional, and global scales. In a broad sense, it represents the average condition of the Earth system. Various lengths of time are used in establishing "average conditions"; 30 years of record, updated every 10 years is a common procedure used for many purposes (this is long enough to eliminate intrannual variations but short enough to not be biased by gradual climatic changes).
CLIMATOLOGY: The study of the long-term state of the Earth's surface, atmosphere, and oceans. See ATMOSPHERIC SCIENCE, meteorology.
CLIMAX: The end result of succession within ecological communities.
COEVOLUTION: In ecology, the evolution of two or more interacting species, under mutual influence on one another. See also TIGHT COEVOLUTION.
COEXISTENCE: The existence of two or more species together within the same habitat.
COMET: A small, icy body that orbits the Sun in a highly elliptical orbit. For more information, see Comets.
(GLOBAL) COMMONS: In general, any resource owned collectively ("held in common") and whose use is shared by a group of individuals; form the practice of some medieval English villages to hold pasturage in common. In the metaphor, Tragedy of the Commons, the global commons is Planet Earth with its many shared resources, animate (e.g., fisheries) and inanimate (e.g., fossil fuels).
COMMUNITY: The collection of organisms and populations of various species within a particular habitat.
COMPACTION: The decrease in a sediments' pore space as the grains are pushed closer together by weight from above.
COMPOUND: In chemistry, the stable combination of atoms of two or more chemical elements.
CONDENSE: To form a liquid from a gas or a vapor. A gas or a vapor may condense when it is cooled or compressed. When the water vapor present in the atmosphere condenses, it forms cloud droplets, rain, fog, or dew.
CONIFER: Cone-bearing trees and shrubs. This includes evergreens, pines, and firs.
CONSTELLATION: An arbitrary formation of stars that, when observed from Earth, is perceived to be a figure or design.
CONTINENTAL CRUST: A crustal plate of relatively light materials floating on the mantle; generally composed of rocks which have the same composition as granite. Thickness ranges from 20 to 90 kilometers; average thickness is ~35 kilometers. See also CRUST, OCEANIC CRUST. For more detail, see Earth's Crust.
CONTINENTAL DRIFT: The theory that over geologic time, continents moved across Earth's surface. This was a predecessor theory eventually absorbed in the theory of plate tectonics.
CONVECTION: motion in a gravitational field arising from density differences. A typical scenario is warm, less dense material rises from the bottom to the top where it cools. Cooler, more dense material sinks from the top to the bottom where it warms. If a continuous loop is created, this is termed a convective roll (2-D) or cell (3-D). Convection is a very efficient form of heat transfer.
COPERNICAN SYSTEM: The theory of the structure of the SOLAR SYSYEM that places the SUN at the center, with the planets moving around it.
CORE: The extremely dense central region of the Earth; all available evidence indicate it consists of a spherical crystalline iron inner core surrounded by a spherical shell of liquid iron termed the outer core.
CORONA: The outermost part of the Sun's atmosphere, above the chromosphere.
CREEP: A common kind of mass wasting in which the ground surface moves imperceptibly downhill.
CRETACEOUS: The third period in the Mesozoic Era, extending from 144 to 65 Million years ago. The name comes from the Latin creta, meaning chalk.
CROSS-BEDDING: Bedsdeposited on an inclined plane.
CRUST: The solid, relatively thin layer of rock forming the outer shell of the geosphere; the outer most layer of the solid part of the planet. Its thickness varies from 5 kilometers (under the oceans) to 90 kilometers (under the continents). Distinction is often made between relatively old, relatively less dense continental crust and relatively young, relatively more dense oceanic crust. See also LITHOSPHERE. For more detail, see Earth's Crust.
CRUSTOE ALGAE: Thin and crusty algae.
CRYOSPHERE: The regions of the Earth System wherein water exists, more or less permanently, in a frozen state. Included are Earth's icecaps, frozen tundra, and mountain glaciers.
CRYPSIS: In ecology, the camouflage patterns that allow organisms to conceal themselves against backgrounds.
DARK HALO: A cloud of dark matter that surrounds the Milky Way's luminous disk and which appears to contain most of the Galaxy's mass.
DARK MATTER: Material that emits little if any light. See Make-up Of The Universe.
DAY: The length of time that a planet takes to complete one rotation about its axis.
DIAMETER: A measure of an object's physical size; the length of an imaginary straight line passing through the object's center.
DECLINATION: Angular distance of an object from the celestial equator, measured in degrees, minutes, and seconds. Declination is analogous to latitude in geography.
DEEP TIME: see GEOLOGIC TIME.
DEGENERATE MATTER: The state of matter in which pressure among subatomic particles (electrons or neutrons) supports a star against inward collapse from its own gravity. In white dwarfs and faded brown dwarfs, the outward pressure of electrons balances the inward force of gravity; in neutron stars, the outward pressure of neutrons balances the inward force of gravity.
DELTA: A triangular-shaped region at the mouth of a river, formed by the river depositing sediment it transports; composed of relatively flat-lying topset and bottomset beds with steeped, cross-bedded, foreset beds between.
DENSITY: Mass divided by volume.
DESERT: An ecosystem suited for hot weather and little water.
DEVONIAN: The fourth period in the Paleozoic Era, extending from 408 Million to 360 Million years ago. Named after Devon in England.
DRUMLIN: A ridge or hill with a smooth summit consisting of material transported by glacial action and deposited when the glacier melted.
DRY WEIGHT: The mass of an organism after all the water has been removed.
DUST: Airborne dust, ash, and debris. Dust can be lofted by winds, fires and volcanoes. In the troposphere, dust usually will be washed out in a few days by precipitation. Dust in the stratosphere can remain aloft for many days, even years.
EARTH: Third planet from the Sun. See also
EARTHQUAKE: A release of mechanical energy due to an abrupt movement along a fault; the released energy is dissipated through seismic waves that spread throughout the Earth.
(ORBITAL) ECCENTRICITY: A measure of an orbit's shape; a dimensionless measure of how circular or how elongated an orbit is. A closed orbit that is perfectly circular has an orbital eccentricity of 0.00; the most elliptical closed orbit possible has an eccentricity just under 1.00. A orbit with an eccentricity of exactly 1.0 is parabolic, while one with an eccentricity of greater than 1.0 is hyperbolic. Both parabolic and hyperbolic orbits are "open"; elliptic and circular orbits are "closed".
ECLIPTIC AXIS: A reference line drawn through Earth's center, normal to the ecliptic plane.
ECLIPTIC PLANE: The plane containing the APPARENT PATH of the SUN in its annual motion around Earth, as projected on the CELESTIAL SPHERE or, equivalently, the plane containing the true path (orbit) of the Earth as seen from the Sun against the background of the Celestial Sphere.
ECOSYSTEM: A community of plant and animal species living together in rough balance and the environment in which they live.
EFFECTIVE PLANETARY TEMPERATURE: The temperature that a planet must have in order to radiate to space, as a BLACKBODY, all the solar energy that it absorbs.
EL NINO: (for more on El Nino)
ELECTROMAGNETIC SPECTRUM: The entire range of electromagnetic radiation. The wavelengths (distance between adjacent peaks) of the electromagnetic waves within the spectrum range from kilometers (for radio waves) to nanometers (for X-rays).
ELECTRON: One of the three main sub-atomic particles found atoms, it carries the basic unit of (negative) electrical charge. Electrons may be found surrounding an atom's nucleus in a particular electronic configuration. They may also exist independently. The electrical charge of an electron is equal but opposite to that of a proton. The mass of an electron is very small, 1/1840th of the mass of the proton and neutron.
(Chemical) ELEMENT: The fundamental types of matter. Each element occurs in the form of atoms containing a number of protons unique to that element. Atoms of 92 different elements are found naturally in the Earth System -- examples: hydrogen, helium, ..., carbon, ..., oxygen, etc... Ten others have been formed artificially, but they are very short-lived. All substances in the Earth System are formed through chemical reactions among combinations of atoms of the basic chemical elements. For more details on selected elements important in the Earth System, see The Elements.
EOCENE: The second epoch in the Tertiary Period, extending from 58 to 37 Million years ago.
EQUINOX: One of the two equinoctial points along a planet's orbit, denoted by the intersection between the plane of a planet's orbit and the Celestial Equator. When the Sun is at one of these two points, the length of day and night is equal everywhere on the planet. For a discussion of solstices on Earth, see Earth's Seasons. See also Solstice.
EROSION: The loosening of soil and rock fragments, and well as their removal downhill or downwind. Gravity, running water, wind, and moving ice masses are means by which erosion proceeds. Erosion may also include the transport of dissolved rock in runoff water. See also WEATHERING.
ESCAPE VELOCITY: The speed necessary for a moving body to overcome the gravitational field of a celestial body.
ESKER: A winding ridge or sediment formed by streams flowing under or in a glacier.
ESSENTIAL ELEMENTS: Elements required by plants to complete their life cycles.
EUKARYOTE: Single-celled microbes with a nucleus. Such cells contain a nucleus (a central element containing all the genetic material -- many fibers -- for the cell) and organelles. The cell wall is relatively simple, since processes such as respiration and photosynthesis are carried out within the cell by the specialized organelles. See also prokaryote.
EVAPORATE: To change from a liquid to a vapor.
EVAPOTRANSPIRATION: The combined loss of water by evaporation from the surface and transpiration from plants.
EVOLUTION: The process by which life has continuously changed and diversified. For more details, see EVOLUTION AND NATURAL SELECTION.
EXFOLIATION: The mechanical weathering of rocks, in which rounded sheets of rock peel off the parent rock or outcrops the way layers peel off an onion.
EXTINCTION: The elimination or disappearance of a species. See also Mass Extinction.
EXTRUSIVE (IGNEOUS) ROCK: Igneous rock that forms from the cooling of lava that has flowed out onto Earth's surface. The cooling of the lava occurs quickly, so that extrusive igneous rocks contain many small crystals and have a fine grain structure. Basalt is an example of an extrusive igneous rock. Also called volcanic igneous rock.
FAR INFRARED RADIATION: ~11% of the solar spectrum is in the far infrared (wavelengths between 1.5l and 20-30l)
FARENHOLZ'S RULE: Parasite speciation patterns often conform to speciation patterns of their hosts.
FAULT: A fracture in the Earth where the two separated sides move relative to each other. See also EARTHQUAKE, FAULT PLANE.
FAULT PLANE: The zone of fractured rock, more or less planar in extent, forming a fault.
FAUNA: The totality of animals or types of animals within a particular region. See also FLORA.
FISSION: The splitting apart of an atomic nucleus, a process that consumes mass and releases energy. See also FUSION.
FITTNESS: The measure of survival and reproductive success of an organism, or a type of organism.
FLARE: A large eruption of hydrogen plasma from the surface of the Sun. Normally these produce bursts of radiation and a stream of charged particles that flow outward from the Sun. The bursts of radiation can damage satellites in orbit around Earth. The charged particles can interact with Earth's magnetic field to produce electromagnetic disturbances that can damage power grids, communication systems, etc…
FLORA: The totality of plants or types of plants within a particular region. See also FAUNA.
FOOD WEB: The network of feeding relationships among the species in a specified region.
FORESET BEDS: See DELTA.
FRACTURE: A rough, uneven break in rock. In mineralogy, the breaking of a mineral along any surface other than a cleavage plane.
FRAMEWORK SILICATE: A silicate mineral in which each silicon atom shares each of its four oxygen partners, in the proportion SiO2.
FREEZING TEMPERATURE: The temperature at which a pure substance changes from liquid to solid.
(THERMONUCLEAR) FUSION: An energy-releasing nuclear reaction in which atoms of a lighter element are combined to produce ("fused") another, heavier element. This is a mass-consuming, energy-releasing reaction. See also FISSION.
GALAXY: A conglomeration of millions, billions, or trillions of stars that are bound together by gravity. The local galaxy is the "Milky Way".
GAS GIANT: A giant planet consisting of a very deep, massive atmosphere of gases such as hydrogen and helium surrounding a small core of rock, water, and ammonia. Because of the great mass of the atmosphere, near the core the atmospheric gases are so compressed it is difficult to decide where atmosphere ends and core begins, that is, it is difficult to identify a planetary surface. The Solar System has two gas giants: Jupiter and Saturn.
GENERAL CIRCULATION MODEL (GCM): A large three-dimensional computer model of the Earth's air-land-water system that is used to explore climate and climate change. The global wind, pressure, temperature, and moisture fields are computed from basic physical equations. Current GCMs are restricted to regional spatial resolution, largely due to the limited capabilities of today's supercomputers.
GENE: The fundamental unit of natural selection. See also RECESSIVE GENES.
GEOCHEMICAL CYCLE: A sequence of RESERVOIRs interconnected by chemical PROCESSES operating on a chemical element in the Earth system. The interconnections form one or more closed LOOPs so that amount of the element in the cycle remains more or less fixed over long time. Account is kept of both the amount of the element located in each reservoir and the rate at which it passes through each process, giving a mass BUDGET for the element in the cycle. Most geochemical cycles also involve ENERGY in various forms, so an ENERGY BUDGET is also required to fully describe the cycle. From a practical perspective, most geochemical cycles are only approximations to the true basic cycles for the chemical elements. Usually there are reservoirs of unknown sizes in the geosphere, and some (perhaps many) of the interconnecting processes are unknown or poorly understood. However, for many purposes and for a restricted period of time, such approximate geochemical cycles are very useful. See also BIOGEOCHEMICAL CYCLE.
GEOCHRONOLOGY: The study of time as applied to Earth, the Solar System, and other planetary systems.
GEOLOGIC TIME (sometimes called "deep time"): The 4.6 Billion year history of Earth, from its origin to the present, as inferred from the rock record, both on Earth and the Moon, and the geochemical make-up of those two bodies. This history is normally divided into a hierarchy of time intervals, often portrayed on a Geologic Time Scale.
GEOLOGY: The scientific discipline that studies the origin, composition, and structure of Planet Earth. See also GEOLOGY for more details.
GEOMORPHOLOGY: The study of the origin, development, and subsequent evolution of land forms on Earth's surface.
GEOSPHERE: The apparently solid component of the Earth System "Apparently" is used here since much of the geosphere is "fluid" at high temperature and pressure. The apparent solid portion of the geosphere -- the outer skin of the planet -- is the crust; see also lithosphere.
GIANT PLANET: A very large planet (taking Earth to be the reference). The Solar System has four giant planets: Jupiter and Saturn, which are gas giants; and Uranus and Neptune, which are ice giants.
GLACIAL TILL: The unsorted sediments dropped by melting ices flows.
GLACIER: A large mass of ice flowing slowly along a valley or down a slope, or spreading out over an area of land.
GLACIOLOGY: Study of the formation, evolution, movement, and physical properties of glaciers and other ice features on Earth's surface.
GLOBULAR CLUSTER: A large grouping of stars, usually associated with a galaxie. About 120 globular clusters orbit the center of the galaxy.
GONDWANALAND: An ancient land mass that included present-day Antarctica, South America, India, Africa, Asia, and Australia.
GRANITE: Coarse-grained, intrusive or plutonic, felsic igneous rock. Composed mainly of quartz and potassium feldspar, with some moscovite mica and biotite mica.
GREENHOUSE EFFECT: Planetary heating by greenhouse gases in the atmosphere.
GREENHOUSE GAS: Any atmospheric gas that only weakly absorbs visible light (i.e., is nearly transparent to sunlight), but which absorbs (and so radiates) in the infrared portion of the electromagnetic spectrum (i.e., are translucent or opaque to infrared radiation). In Earth's atmosphere, important greenhouse gases include water vapor, carbon dioxide, and methane.
Hadean or Pre-Archean: The first eon of geologic time; named for Hades, the Roman god of the underworld. For more detail, see the Geologic Time Scale.
HABITAT: The environment in which an organism, population, or community exists.
HAPLO-DIPLOID: The genetic system in which one sex arises from unfertilized eggs, so that, for example, additional …..
HEAVY METALS: Those metals that have densities greater than 5 g cm-3 (for a list).
HECTARE: A unit of land area equaling 100 by 100 meters (1 hectare = 2.47 acres).
HELIOPAUSE: The outer edge or limit of the heliosphere. Beyond the heliopause, the Sun's emissions of particles and its magnetic field are not detectable above the background of galactic space.
HELIOSPHERE: The region of space over which the Sun's emissions of particles and its magnetic field are dominant. Bounded by the heliopause.
HELIUM: See The Chemical Elements.
HOLOCENE: The second (and current) epoch in the Quatarnary Period, extending from 10,000 years ago to the present to 10,000 years ago.
HYDROGEN: See The Chemical Elements.
HYDROLOGIC CYCLE: The circulation of water among the atmosphere, geosphere, hydrosphere, and the biota. Often termed the "water cycle".
HYDROLOGY: Study of the abundance and movement of water on and beneath Earth's surface.
HYDROSPHERE: The water portions of the Earth System. This includes water as liquid in the oceans, lakes, and in the ground, as vapor in the air, and as ice in the polar regions.
ICE GIANT: The term occasionally used to characterize Uranus and Neptune, giant plants that are not gas giants. Such planets consist mostly of a core of "ices" -- of water, methane, and ammonia -- surrounded by a moderately thick atmosphere of hydrogen and helium.
IGNEOUS ROCK: Rock formed by crystallization from magma. There are two general types of igneous rock, based on silicon content: silicic and mafic. Igneous rock is also classified on the basis of the way it is formed: intrusive or plutonic, and extrusive or volcanic.
(ORBITAL) INCLINATION: A measure of the tilt of an orbital plane, measured relative to the ecliptic plane; the angle between the plane of an object's orbit around the Sun and the plane containing Earth's orbit.
INFRARED RADIATION: The region of the electromagnetic specturm with wavelengths somewhat longer than that of visible light; specifically, light with wavelengths between about 1 micron (visible light) and 1 mm (microwaves).
INSOLATION: INcoming SOlar radiATION.
INTRUSIVE (IGNEOUS) ROCK: Igneous rock formed deep in the crust, where the cooling process leading to solidification of the magma occurs slowly due to the insulation provided by the surrounding rocks. As a consequence, intrusive igneous rocks contain large crystals and have a course grain structure. Grabbo is an example of an intrusive igneous rock. Also called plutonic rocks.
INVERTEBRATE: An animal without an internal backbone. See also VERTEBRATE.
ION: An atom or group of bonded atoms that has gained or lost one or more electrons, becoming negatively or positively charged, respectively. Positive charged ions are terms cations; negatively charged ions, anions.
ISOLATED TETRAHEDRA: A silicate mineral in which one silicon atom is bonded to four oxygen atoms, as in SiO4.
ISOTOPE: An atom of a chemical element having a specific number of neutrons in its nucleus. Some elements can have several isotopes. Isotopes of an element have the same atomic number, different atomic masses, identical chemical properties, and (usually) very slightly different physical properties. Some isotopes of an element can be radioactive, while others are stable.
JUNGLE: Also know as tropical forest. A biome that thrives in hot, wet climates.
JURASSIC: The second period in the Mesozoic Era, extending from 208 to 144 Million years ago. Named after the Jura Mountains in east-central France.
KELVIN (K): The unit of temperature on the "absolute temperature" scale. This scale starts at the coldest possible temperature, 0K ~ -460° F. Room temperature is about 295K.
KETTLE: A depression in the surface caused by the melting of a large piece of subsurface ice after a moraine had formed.
KINGDOM: The most general classification of life; the next level of classification is Phylum. The five recognized kingdoms are prokaryotae, protoctista (eukaryotes), fungi, plantae, and animalia.
KUIPER BELT: See Make Up Of The Solar System and The Kuiper Belt.
LAND FORM: The shapes of the Earth's surface features; these occur on both the large and small scales, and are evidence of the operation of various geologic, atmospheric, hydrospheric, and cryospheric processes; an example of a large scale feature is the Rocky Mountains (formed by tectonic processes and shaped by water) while an example of a smaller scale feature is a glacial morrine (deposited by a retreating glacier).
LA NINA: See also El Nino and Southern Oscillation.
LATITUDE:
LAVA: The lighter forms of magma that reach the surface via upwellings and volcanoes. See also AA.
LICHEN:
LIFE CYCLE:
LIGHT-YEAR: The distance traveled by light in one year, ~5.88 Trillion miles.
LIMESTONE: A sedimentary rock, predominately composed of the mineral calcite, where the material forming the rock is originally deposited by either chemical precipitation or biological processes.
LITHIFICATION: The process in which sediments are transformed into rock. See also SEDIMENTARY ROCK.
LITHOSPHERE: The solid, outer layer of the geosphere. The crust and the uppermost portion of the mantle comprise the lithosphere.
LUNAR ECLIPSE: A lunar eclipse occurs when Earth passes directly between the Moon and the Sun; this occurs only during a Full Moon (though only a very few Full Moon's produce lunar eclipses). When the Moon passes into Earth's shadow (see UMBRA), the sunlight illuminating the Moon is partially (i.e., a partial lunar eclipse) or wholly (i.e., a total lunar eclipse) blocked. See also SOLAR ECLIPSE.
LUNAR MONTH: The period of one complete revolution of the Moon around the Earth or, equivalently, the interval between subsequent occurrences of the same phase of the Moon. This defines the synodical month of 29 days, 12 hours, 44 minutes, 2.8 seconds.
MAFIC (adj): Igneous rock, magma, or lava that is rich in the denser, darker colored silicate minerals. Contains 45 to 52% silica and is rich in magnesium and iron. Mafic magma and lava are hot (~1200 C) and very fluid, and so can flow rapidly and for long distances. Mafic minerals, including pyroxene, amphibole, and biotite mica, are dark in color. Basalt and grabbo are examples of mafic rocks. See also AA, SILICIC, ULTRAMAFIC.
MAGMA: Molten rock. There are two general types of magma, based on silicon content: silicic and mafic. It may contain dissolved gases and solid mineral crystals. Very dense magma comprises the mantle. See also IGENEOUS ROCK, LAVA.
MANTLE: The spherical shell of magma between the crust and the core. For more detail, see Earth's Mantle.
MARE (plural - MARIA): Broad dark areas on the surface of the Moon.
MASS: The amount of material in a object. The amount of mass in object determines the strength of its gravitational pull on other objects.
MASS EXTINCTION: At various times in Earth's history, large numbers of species -- between 5 and 50% of all species then extant -- have vanished in apparently short periods of time. See also extinction.
MELTING TEMPERATURE: The temperature at which a pure substance change from a solid to a liquid.
MERIDIONAL ENERGY DISTRIBUTION:
MESOZOIC: The second era of the Phanerozoic eon in geologic time, extending from 245 to 65 Million years ago. "Middle life" in Latin. For more detail, see the Geologic Time Scale.
METAL: An element which, in pure form, exhibits many of the following properties or characteristics:
Strong and hard
Malleable and ductile
Produces cations
Reacts with acids and non-metals
Produces basic oxides
Conducts heat and/or electricity
Melts and boils only at high temperatures
METAMORPHIC ROCK: Rock that has been modified, but not completely melted, by high temperature and high pressure. Through chemical processes that proceed at high temperature and pressure, the nature of the minerals in the rock changes.
METAZOAN: A multicelluar animal that possess more than one kind of cell and are organized into tissue and organs.
METEOROLOGY: The sub-discipline of ATMOSPHERIC SCIENCE focused on the study of the occurrence of a wide range of phenomena in real time in Earth's atmosphere, i.e., on "weather".
METHANE: CH4; consists of atoms of carbon and hydrogen, two of the most common substances in the Universe.
MICROBE: A single-celled organism. There are two types of microbes: prokaryotes and eukaryotes.
MICRON: a short expression for "micrometer" (10-6 m).
MILKY WAY: The galaxy in which the Solar System resides; it is a "giant" galaxy, with at least ten lesser galaxies revolving around it. The nearest giant galaxy to the Milky Way is Andromeda.
MINERAL: A naturally occurring substance that has a uniform chemical composition and a characteristic crystalline structure. Minerals are classifed into groups. See also amorphous solids.
MINERAL GROUP: More than 2500 different minerals have been identified. For purposes of classification, each is assigned to one of thirteen groups based on common properties. Most rock-forming minerals are found in one of seven of these groups. The largest and most complex group is the silicates.
MIOCENE: The fourth epoch in the Tertiary Period, extending from 24 to 5 Million years ago.
MISSISSIPIAN: A period in the Paleozoic Era, extending from 360 to 320 Million years ago. Named after the State of Mississippi.
MOHOROVICIC DISCONTINUITY (MOHO): The turbulent region between the crust and the mantle. The MOHO is observable in seismic maps of Earth's interior.
MOON: A natural object that revolves around a planet. Earth's moon is often referred to as "the Moon".
MORAINE: A ridge of sediment deposited at the sides or end of a glacier.
MOSCOVITE MICA: A common rock-forming silicate, generally colorless and ranking #4 on the Mohs scale of hardness. It has a variable chemical composition of potassium, magnesium, silicon, and oxygen, with water in its crystalline structure. See also MICA, BIOTITE MICA.
MUTATE: When an organism makes an inexact copy of itself. This occurs naturally and provides the variability which allows evolution to occur.
NANOMETER: One billionth of a meter (10-9 m).
NATURAL SELECTION: The process that translates differential success in survival and reproduction in a population of an organism into evolutionary change. For more details, see EVOLUTION AND NATURAL SELECTION.
NEAR INFRARED RADIATION (NIR): ?37% in the near infrared (wavelengths between 0.7l and 1.5l microns)
NEUTRON: One of the three main sub-atomic particles found in the nuclei of atoms. They may also exist independently. The neutron has the same mass as a proton, but carries no electrical charge. See also electron.
NEWTON: The unit of force in the MKS system; the force required to accelerate a unit mass (1 kilogram) by one unit of acceleration (1 m s-2). It derives from Newton's Second Law of Motion.
NICHE: The role of a particular species within its community.
NIMBY: Acronym for "not in my back yard".
NITRIFICATION: The oxidation of ammonia to produce nitrates that plants can easily assimilate.
NITROGEN CYCLE: The cycling of nitrogen through the processes of nitrogen fixation, nitrification, and denitrification.
NITROGEN FIXATION: The conversion of gaseous nitrogen into other compounds, such as ammonium and ammonia, making it available for oxidation for energy or assimilation by some organisms.
NON-METAL: An element that, in pure form, exhibits many of the following properties or characteristics:
Forms covalent compounds
Gives rise to anions
Does not react with acids
Produces acidic oxides
Conducts heat and electricity only poorly
Gaseous at room temperature, or melts and boils at low temperatures
NUTATION: The "nodding" motion in the curve traced out by the CELESTIAL POLE due to PRECESSION. This motion appears as small-amplitude (~9"), short-period (~19 years) fluctuations in TILT superimposed on the long-period change in axial orientation.
OBLIQUITY: The angle made by a planet's rotation axis with respect to a line drawn through the center of the planet and perpendicular to the plane of the planet's orbit. Also called Axial Tilt.
OCEANOGRAPHY: The scientific discipline focused on the study of Earth's oceans, the seafloor and the overlying sediments, the chemistry of ocean waters, and marine life forms. See OCEANOGRAPHY.
OLIGOCENE: The third epoch in the Tertiary Period, extending from 37 to 24 Million years ago.
OLIVINE: A common rock-forming silicate, apple-green in color and ranking #8 on the Mohs scale of hardness. It has a variable chemical composition of iron, magnesium, silicon, and oxygen.
ONTOGENY: The sequence of stages in the development of an organism from birth to adult.
OORT CLOUD: A vast spherical shell of icy bodies surrounding the Solar System; these bodies orbit at large distances from the Sun, well beyond the orbit of Pluto. See Make Up Of The Solar System and The Oort Cloud.
OOZE: Fine particle sediment that contains a high percentage (30% or more) of organic matter.
OPPORTUNISTIC: A species that exploits transient environmental opportunities.
ORBIT: The path one body follows around another.
ORBITAL ECCENTRICITY: see ECCENTRICITY.
ORBITAL PERIOD: The time a body takes to revolve around another. In general, the further apart the two bodies are, the longer the orbital period.
ORBITAL INCLINATION: see INCLINATION.
ORDER: The classification of life under Class. The major orders of mammals are rodents, felines, canines, ruminants, primates, and cetaceans.
ORDOVICIAN: The second period in the Paleozoic Era, lasting from 505 Million to 438 Million years ago; named after an ancient Celtic tribe from Wales.
ORE: Rock mined from a deposit that contains commercially useful minerals or elements.
ORGANISM: An independent unit of life -- all individual plants, animals, and microbes are organisms.
OROGENESIS: The process by which mountain belts are formed.
OROGENY: The process of forming mountains.
OUTWASH PLAIN: A broad, flat area created when a glacier
OXIDATION: (a) Originally, any chemical reaction with oxygen. (b) More generally, any chemical reaction involving the loss of electrons by a substance. See also REDUCTION.
OXYGEN: See The Chemical Elements.
OZONE: (O3) A molecule containing three oxygen atoms (O3) which shields Earth's surface from deadly ultraviolet radiation. It is also a greenhouse gas that absorbs some of Earth's warmth; a subsequent re-emission returns part of this energy to the surface.
PANGEA:
PALEONTOLOGY: The study of the structure, environment, evolution, and distribution of extinct organisms through their fossil remains. Subdisciplines include paleobotany, paleoecology, and paleozoology.
PALEOCENE: The first (and oldest) epoch in the Tertiary Period, extending from 65 to 58 Million years ago.
PALEOZOIC: The first era of the Phanerozoic eon in geologic time, extending from 570 to 245 Million years ago. "Old life" in Latin. For more detail, see the Geologic Time Scale.
PANGEA: Wegner's name for the supercontinent that existed when all the continents were joined in one landmass
PARASITE: An individual or species that exploits another individual (the host) or individuals, especially of a different species.
PATHOGEN: An organism that causes disease.
PEBBLE: A clastic fragment between 4 to 64 millimeters (~1/6 to 2.5 inches) in size.
PENNSYLVANIAN: A period in the Paleozoic Era, lasting from 320 to 286 Million years ago. Named after the state of Pennsylvania. See also CARBONIFEROUS.
PERIHELION: The point in Earth's orbit when it is nearest the Sun. (The more general term is perigee.) See also APHELION.
PERIOD: See also ORBITAL PERIOD, PERIODIC.
PERIODIC TABLE: A two-dimensional tabular arrangement portraying the elements in terms of similarities and differences in chemical properties. For more detail, see The Periodic Table.
PERMIAN: The most recent period of the Paleozoic Era, running from 260 to 245 Million years ago. Named after an area in Russia called the Perm.
PETAGRAM (Pg): 1 petagram = 1015 grams
PHANEROZOIC: The fourth and current eon in geologic time, running from 570 Million years ago to the present day; means "abundant life". For more detail, see the Geologic Time Scale.
PHASES OF THE MOON: The sequence of shapes of the illuminated potion of the Moon's surface as observed from Earth. The phases result from the continually changing relative positions of the Sun, the Moon, and Earth. The sequence repeats each lunar month. See also NEW MOON, FULL MOON.
PHOTIC ZONE: The upper zone of a body of water, as defined by the depth to which sunlight penetrates.
PHOTOSPHERE: The visible surface of a star; the source of the light emitted by a star. See THE SUN for details regarding the photosphere of the Sun.
PHOTOSYNTHESIS: A photochemical process in many plants that converts electromagnetic energy (light) into chemical energy, i.e., carbon dioxide and water into energy-storing chemicals such as sugars; oxygen is a byproduct. In the plants, the green pigment chlorophyll absorbs sunlight and catalyzes the reaction. Photosynthesis is the primary source of food for almost all life on Earth, while the released oxygen maintains the level of that gas in Earth's atmosphere.
PHYLUM: The classification of life under Kingdom. The major animal phylums are chordates, arthropods, and invertebrates.
PHYSICAL OCEANOGRAPHY: The study of Earth's oceans with a focus on motions on all scales and the physical processes that drive them.
PHYTOMASS: The dry weight of a plant. The planetary phytomass is the total dry weight of all plant material on the planet. See also BIOMASS.
PHYTOPLANKTON: Tiny drifting plants, especially algae, that live in the photic zone of water bodies. Phytoplankton form the bottom trophic level of oceanic food webs. See also PLANKTON, ZOOPLANKTON.
PILOCENE: The fifth (and most recent) epoch in the Tertiary Period, extending from 5 to 1.6 Million years ago.
PLAGIOCLASE: A common rock-forming silicate that is part of the feldspar group, often white to gray in color. It ranks #6 on the Mohrs scale of hardness. Composed of sodium, calcium, alumninum, silicon, and oxygen.
PLANT: An organism that uses photosynthesis to feed itself.
PLANET: A reasonably large astral body that orbits a star. A planet does not emit light but simply reflects the light that strikes it. For an object to be considered a planet, it mass must be more than Pluto's but not much more than Jupiter's.
PLANETISIMAL: A relatively small (usually taken to be Moon-size or less) asteroid-like body. In young star systems, planetisimals may accumulate through collisions to form planets.
PLASMA: A collection charged particles (positive ions; electrons) that exhibits the properties of a gas, but in addition conducts electricity and is affected by magnetic fields.
PLATE: A solid piece of Earth's crust which floats on the mantle and moves with the convection currents in the mantle.
PLATE TECTONICS: A widely accepted theory that Earth's crust is formed of distinct plates moving with convection currents in the mantle. It provides explanations for such geological phenomena as earthquakes and volcanoes.
PLEISTOCENE: The first (and oldest) epoch in the Quatarnary Period, extending from 1.6 Million to 10,000 years ago.
PLUTON: A body of plutonic igneous rock. See also BATHOLITH.
PLUTONIC IGNEOUS ROCK: Rock formed from magma with the Earth; the magma intrudes through existing (older layers) of rock. Also called intrusive igneous rock. Named after Pluto, the Roman god of the underworld. See also PLUTON.
POPULATION: The totality of individual members of a species within a particular region.
POPULATION GENETICS: The study of genetic variations and changes with a population.
PRE-CAMBRIAN: All of geologic time before 570 Million years ago; includes the first three eons of the geologic time scale. For more detail, see the Geologic Time Scale. See also CAMBRIAN, GEOLOGIC TIME.
PRE-MAIN-SEQUENCE STAR: A star so young that it has not yet reached the main sequence. Such a star does not fuse hydrogen into helium, but it does shine, by converting gravitational energy into heat.
PRECESSION: The gradual shifting of Earth's axis of rotation around the ecliptic axis. Precession forced by the gravitational pull of the Moon on the bulge at the Earth's equator. This change in axis orientation causes the westward motion of the equinoxes and the movement of the CELESTIAL POLEs among the fixed stars. The change in orientation has a period of about 28,500 years. Note that precession describes a change in orientation, not in mean inclination (see TILT).
PREDATOR: An animal that hunts and kills others for food. See also PREY.
PREY: An animal that is hunted or killed for food by another. See also PREDATOR.
PRIMARY PRODUCTION: The assimilation of solar energy by plants.
PRIMARY PRODUCTIVITY: The rate of assimilation of solar energy by plants.
PRIMARY SUCCESSION: The sequence of species colonizing an area after a novel disturbance, such as a lava flow. See also SUCCESSION, SECONDARY SUCCESSION.
PRIVATIZATION: The transfer of property rights from the state or government to individuals and corporations.
PROKARYOTE: Single-celled microbes with no nucleus. In such simple cells, the genetic material exists as a single fiber. In prokaryotes, the cell wall is complex, and controls such processes as respiration and photosynthesis. See also EUKARYOTE.
PROMINENCE: On the Sun, a rising plume of ionized gas which follows along magnetic field lines.
PROTEIN: A long chain of amino acids.
PROTEROZOIC: The third eon in geologic time, lasting from 2.5 Billion to 570 Million years ago. The name means "former life". For more detail, see the Geologic Time Scale.
PROTON: One of the three main sub-atomic particles found in the nuclei of atoms, it carries the basic unit of (positive) electrical charge. They may also exist independently. The electrical charge of a proton is equal and opposite that of an electron. The mass of a proton is the same as that of a neutron. The number of protons in an atom is given by its atomic number. Isotopes of any element contain the same number of protons.
P-WAVE: P = primary wave. Body waves generated by an earthquake. P-waves travel through the Earth at 6 to 14 km s-1 (the fastest of all seismic waves) and so are the first to arrive at a point on the Earth's surface. See also S-WAVE.
PYROCLASTIC MATERIALS: Literally, "fire fragments". The solid pieces of igneous material that are expelled (often violently) from a volcano.
PYROXENE: A common rock-forming silicate, often dark in color. It ranks #6 on the Mohrs scale of hardness. It has a chemical composition of calcium, iron, magnesium, silicon, oxygen, and traces of many other elements.
QUARTZ: The hardest common rock-forming mineral, ranking #7 on the Mohs scale of hardness. It has a chemical composition of pure silicon, with the silicon atoms packed in a three-dimensional structure of silica tetrahedra quartz. It is very resistant to erosion and is found in many sedimentary and metamorphic rocks.
QUATERNARY: The second period of the Cenozoic Era, lasting from 1.6 Million years ago to the present. The name has been carried forward from an earlier naming scheme for geologic time: primary (before life); secondary (old, unusual life); Tertiary (life close to today), and Quaternary (life like today).
QUENCHED: Cooled very quickly.
RADIATE: (a) To emit electromagnetic radiation. (b) The Class of invertebrates that includes jellyfish and starfish.
RADIOACTIVE: A characteristic of the nuclei of certain isotopes of certain elements. These nuclei spontaneously disintegrate, emitting nuclear particles and electromagnetic waves. The result may be a different isotope of the original element, or a different element. In each case, the result has a lesser atomic mass.
RADIOMETRIC DATING: The determination of the age of a sample of material through the measurement of the quantities present in the sample of certain radioactive isotopes.
REALIZED BIOTA: The assemblage of species found within a particular region. See also BIOTA.
REALIZED NICHE: The range of conditions under which a species is found. See also NICHE.
RECESSIVE: Forms of genes (alleles) that have no effect unless inherited from both parents.
REDUCTION: See also OXIDATION.
RESISTANCE: The ability of a host to sustain itself again a parasite or a bacterium to sustain itself against an antibiotic.
RESPIRATION: Chemical reactions by which organisms -- both plants and animals -- release the energy stored in food (i.e., in sugars such as glucose). Respiration may occur with or without oxygen.
Anaerobic respiration rearranges the molecular structure of the sugars to produce energy. By-products are lactic acid, or ethanol and carbon dioxide.
ROCK: An aggregation of minerals. There are three types of rock: igneous; metamorphic; and sedimentary. Rock forms the crust, the truly solid part of the earth subsystem.
ROTATE (ROTATION): To spin about an axis. Should not be confused or used interchangeably with Revolve.
SAND: Sedimentary fragment between 1/16 and 2 millimeters in size. SAND BAR: In the ocean, a body of sand deposited offshore; may or may not be above sea level. See also BARRIER ISLAND.
SANDSTONE: A clastic sedimentary rock composed of fragments between 1/16 and 2 millimeters in size.
SATELLITE: A lesser object that orbits another. In most cases, the term refers to a small moon revolving around a planet. See MOON.
SCLEROPHYLLS: Plants with hard leaves.
SEARCH IMAGE: The mental image a predator uses in searching for prey.
SECONDARY SUCCESSION: The sequence of species recolonizing a space after a common disturbance, such as a treefall or a fire. See also SUCCESION, PRIMARY SUCCESSION.
SEDIMENT: Solid fragments resulting from the weathering of rocks. Usually unconsolidated (loose), the fragments may be transported and then deposited by wind, water, and ice.
SEDIMENTARY ROCK: Rock formed from sediments through lithification, compaction, and cementation.
SEISMIC WAVE: Energy wave generated by an earthquake. See also BODY WAVE, P-WAVE, SURFACE WAVE, S-WAVE.
SELECTION: See NATURAL SELECTION.
SHEET SILICATE: A silicate mineral in which each silicon atom shares three of its four oxygen partners, in the proportion Si2O5.
SHIFTING BALANCE THEORY: A fundamental theory, developed by Sewall Wright, of evolutionary change over heterogeneous environments.
SIDEREAL (PERIOD): The time required for a body to make a complete rotation or revolution relative to the distant (fixed) stars.
SILICATE MINERAL: Minerals containing silicon comprise the largest and most complex of the mineral groups. Silicate minerals also the most commonly encountered -- 92% of Earth's crust is made of rocks comprised of silicate minerals. The silicate mineral group is large and complex because silicon and oxygen can combine with each other and with other minerals in many different ways. The four sets of silicate mineral subgroups are isolated tetrahedra, chain silicate, sheet silicate, and framework silicate.
SILICIC (adj): Igneous rock , magma, or lava that is rich in light-density, usually light-colored silicate minerals. Granite is a silicic rock. See also MAFIC.
SILURIAN: The third period in the Paleozoic Era, extending from 438 Million to 408 Million years ago; named after a Celtic tribe in Wales.
SOLAR ECLIPSE: A solar eclipse occurs when the Moon passes directly between Earth and the Sun; this occurs only during a New Moon (though only a very few New Moon's produce solar eclipses). When Earth passes into the Moon's shadow, sunlight illuminating Earth (and an Earthbound observer's view of the Sun) is partially or wholly blocked, depending on the location of an observer on Earth's surface. This gives rise to a partial solar eclipse (when the observer is in the penumbra) or a total solar eclipse (when the observer is in the Moon's umbra), respectively. See also LUNAR ECLIPSE.
SOLAR MASS: The amount of mass in the Sun, and the unit in which stellar masses are usually expressed.
SOLAR SYSTEM:
SOLSTICE: The two points along a planet's orbit where the extremes in solar DECLINATION occur. The solstices are half way between the equinoctial points. For a discussion of solstices on Earth, see Earth's Seasons. See also Equinox.
SOUTHERN OSCILLATION: See also El Nino and La Nina.
SPECIATION: The process(es) by which new species are formed.
SPECIES: In general, a group of organisms that can potentially breed with each other to produce fertile offspring and cannot breed with the members of other such groups.
SPECIES-AREA CURVE: The relationship between the area of a region and the number of species found therein.
SPICULE: A relatively small, spike-like, short duration ejection of plasma from the solar chromosphere.
STAR: A self-luminous celestial body, such as the Sun. There are many types of stars. See also also MAIN SEQUENCE.
STRATIGRAPHY: The study of the origin, composition, sequence, and correlation of rock strata.
SUB-SOLAR POINT: The point of intersection with the Earth's surface of the line joining the center of the Sun with the center of the Earth. This moves north and south in annual cycle as Earth moves along its orbit.
SUCCESSION: The sequence of species colonizing a region, especially following a distrubance. See also PRIMARY SUCCESSION, SECONDARY SUCCESSION.
SUN: The local star around which Earth orbits. (More information on the Sun)
SUNSPOT: Relatively dark areas in the Sun's photosphere. (More information on sunspots)
SUPERORGANISM: The concept of the ecological community, the ecosystem, or the biosphere as an ecological and evolutionary unit.
SURFACE WAVE: Seismic waves that travel along the surface of the Earth. See also BODY WAVE.
SUSCEPTABILITY: A measure of the propensity of a host to succumb to a parasite, or of a bacterium to succumb to an antibiotic.
SUSTAINABLE STEWARDSHIP: Economic development in a region in ways that can be sustained.
SWAMP: See Tropical Grassland.
S-WAVE: S = secondary wave. Body waves generated by an earthquake. S-waves travel through the Earth at speeds of 4 to 7 km s-1 and so arrive at point on the Earth's surface after the P-waves.
SYNCLINE: See also ANTICLINE.
TEMPERATURE: A measure of the amount of heat/thermal energy contained in a mass of material.
TERMINATOR: The great circle boundary between the illuminated and dark portions of the Earth.
THERMOHALINE CONVECTION: Salty and/or colder water is denser than regular seawater. Thus, cold, salty surface water sinks into the deep ocean while warm, fresh water rises and floats on regular seawater.
TERTIARY: The earliest of the two periods of the Cenozoic Era, lasting from 66 to 1.6 Million years ago. The name has been carried forward from an earlier naming scheme for geologic time: primary (before life); secondary (old, unusual life); Tertiary (life close to today), and Quaternary (life like today).
TIDAL FORCE: The perceived force on a body generated by the difference across the body in the strength of the gravitational field of a second body. This difference arises from the fact that gravitational field strength varies inversely with the square of distance. Consequently, the side of the Earth nearest the Moon experiences a slightly stronger gravitational force from the Moon than will the side of the Earth farthest from the Moon.
TIGHT COEVOLUTION: In ecology, coevolution among a number of species that interact strongly.
TILT: The angular difference between the ecliptic axis. At present, EARTH's axis of rotation has a mean tilt of about 23° 27'; it is currently oriented so that the North CELESTIAL POLE is near the fixed star Polaris (the "North Star"). There are both short and long term variations in the degree of tilt and its orientation. See PRECESSION, NUTATION.
TOPSET BEDS: See DELTA.
TRAGEDY OF THE COMMONS: The metaphor, first put forth by Garret Hardin, that though humankind lives in a global commons, individuals tend practice selfish behaviors that, over the long term, are not in the common good and lead to overexploitation of resources.
TRAIT: In ecology, a characteristic of an organism.
TRAIT GROUP: Notion introduced by David Sloan Wilson of a group of individuals that share a common trait.
TRIASSIC: The first period in the Mesozoic Era, extending from 245 to 208 Million years ago. Named for the fact that this is the third of the three divisions of this era, as first determined in Germany.
TROPHIC LEVEL: Number of steps energy must take from the Sun to reach a particular species, through a chain of consumption of one species by another.
TROPHIC PYRAMID: The conceptualization of the trophic web in which higher trophic levels capture less energy.
TROPHIC WEB: The network of energy flow in a community; see also FOOD WEB.
TUFF: Consolidated pyroclastic material. See also WELDED TUFF.
TUNDRA: A biome evolved to survive periodic arctic conditions and year-round cold weather.
TURBIDITE ENVIRONMENTS: Deposits on underwater marine slopes (continental slopes).
TURF ALGAE: Algae that exhibit very dense growth.
TURNOVER RATE: In ecology, the rate of species replacement on an island or in another habitat.
ULTRAMAFIC (adj): An igneous rock, magma, or lava with a composition that has less than 42% silica, and is rich in iron and magnesium; generally dark in color. Compare with MAFIC.
ULTRAVIOLET RADIATION (UV): Radiation with wavelengths somewhat shorter than that of visible light. For radiation from the Sun, ~7% of the energy is in the ultraviolet, at wavelengths between 0.25 m and 0.4 m, though this fraction is quite variable, depending the degree of activity of the Sun. Need to define UV-A, UV-B, UV-C.
UMBRA: Earth's shadow. This is a right circular cone-shaped region whose axis extends directly away from the Sun. The terminator is the base of the cone; it extends for xxxxxx km from the Earth. See also LUNAR ECLIPSE.
UNCONFORMITY: A gap in the rock sequence of a particular locality.
UNIFORMITARIANISM: The assumption that geological processes we see in action today operated in similar ways in the past.
UNLOADING: See EXFOLIATION.
UPLIFT: A force that raises a sequence of rock, often due to stress or buoyancy.
UPTAKE: Assimilation of nutrients from the environment.
UPWELLING: In general, material rising from below. In the ocean, upwelling typically occurs along the western edges of continents (eastern edges of oceans). In Earth's crust, upwelling of magma occurs at mid-ocean ridges to produce new oceanic plate material. See also PLATE TECTONICS.
U-Shaped Valley: Typical shape of a valley carved out by a glacier. See also V-SHAPED VALLEY.
VALLEY GLACIER: A small glacier, confined within a mountain valley.
VARIABLE STAR: A star whose brightness changes, usually in a periodic fashion.
VARIATION: Genetically determined differences in the characteristics of members of the same species.
VARVE: A thin layer of clay sediment. Sequences of varves of alternating light and dark colors are common in some areas of the world, such as Scandinavia. The light varves correspond to winter deposition, the dark ones to summer deposition.
VECTOR: a) In mathematics and mechanics, a quantity having both magnitude and direction. b) In epidemiology, an organism or species that carries agents of disease from host organism to another.
VELOCITY: In mechanics, a vector giving the both speed and direction of motion.
VERTEBRATE: Possessing an internal backbone; one ways of classifying animals. See also INVERTEBRATE.
VIRULENCE: Measure of the degree of pathogenicity of a parasite, or of the population level (titer) it can reach in a host organism.
VISIBLE RADIATION: Electromagnetic radiation with wavelengths between 0.4l (violet) and 0.7l (red). About 44% of the Sun's output is visible radiation.
VOLCANO: A vent in Earth's surface through which magma and pyroclastic fragments erupt. Named after Vulcan, the Roman god of fire.
VOLCANIC EDIFICE: The physical structure of a volcano.
VOLCANIC IGNEOUS ROCK: Rock formed from lava or pyroclastic material on Earth's surface; also called intrusive igneous rock.
V-SHAPED VALLEY: Typical shape of a valley carved by a stream. Compare with U-SHAPED VALLEY.
WATER: H20; a substance whose molecules consist of atoms of hydrogen and oxygen, the two most abundant reactive elements in the Universe. For more information, see
Water molecules are bipolar, that is, they have a positively charged side and a negatively charged side, which accounts for many of the special properties of water. The weak charges on the molecule help break down minerals during chemical weathering.
WAVE: The up-and-down movement of water due to an oscillatory movement of water molecules.
WAVELENGTH: The distance from one wave crest to the next.
WAVE REFRACTION: The behavior of a wave that slows down and bends in a direction more parallel to the shore.
WEATHER: The current STATE of the ATMOSPHERE, usually expressed in terms of instantaneous values of TEMPERATURE, PRESSURE, moisture content, wind, surface conditions, etc..., and in terms of the existing organized patterns of these quantities on local, regional, and global scales.
WEATHERING: The physical disintegration (breakup) of rock into fragments or its going into solution, generally through processes acting on its surface. Weathering of rock may occur due to action of water, ice, freeze-thaw/hot-cold cycling, and abrasion, and the actions of living things. Weathering may break up and chemically change rock, transforming it into a component of soil. The rock fragments or the solutions produced by weathering may then be transported by erosion processes. See also EXFOLIATION.
WELDED TUFF: Rock formed from pyroclastic materials so hot that the materials fuse together. See also TUFF.
YEAR: The length of time that a planet takes to revolve once around its star. The further the planet from the star, the longer its year.
ZOOMASS: The dry weight of an animal. The planetary zoomass is the total dry weight of all animal material on the planet. See biomass.
ZOOPLANKTON: Tiny drifting animals, especially the fish larvae and invertebrates found in the upper level of water bodies.