Earth Science Glossary

(Most definitions taken from Earth Science 11e)

(Last update - July 27, 2008)



§  0/00 – The symbol for parts per thousand.

§  Aa – A type of lave flow that has a jagged blocky surface.

§  Ablation – A general term for the loss of ice and snow from a glacier

§  Abrasion – The grinding and scraping of a rock surface by the friction and impact of rock particles carried by water, wind, or ice.

§  Absolute Humidity – The weight of water vapor in a given volume of air (usually expressed in grams/m3

§  Absolute instability - Air that has a lapse rate greater than the dry adiabat­ic rate.

§  Absolute magnitude - The apparent brightness of a star if it were viewed from a distance of 10 parsecs (32.6 light-years). Used to compare the true brightness of stars.

§  Absolute stability - Air with a lapse rate less than the wet adiabatic rate.

§  Absorption Spectrum - A continuous spectrum with dark lines superim­posed.

§  Abyssal plain -  Very level area of the deep-ocean floor, usually lying at the foot of the continental rise

§  Abyssal zone -  A subdivision of the benthic zone characterized by extremely high pressures, low temperatures, low oxygen, few nutrients, and no sunlight

§  Accretionary wedge A large wedge-shaped mass of sediment that accumu­lates in subduction zones. Here sediment is scraped from the subduct­ing oceanic plate and accreted to the overriding crustal block.

§  Acid precipitation - Rain or snow with a pH value that is less than the pH of unpolluted (?)  precipitation

§  Active continental margin - Usually narrow and consisting of highly de­formed sediments. They occur where oceanic lithosphere is being subducted beneath the margin of a continent.

§  Adiabatic temperature change - Cooling or warming of air caused when air is allowed to expand or is compressed, not because heat is added or subtracted.  Dry air changes at 10°C/1,000m, and wet air (condensation has begun) changes at 5-9°C/1,000m.

§  Advection - Horizontal convective motion, such as wind.

§  Advection fog - A fog formed when warm, moist air is blown over a cool surface.

§  Aerosols - Tiny solid and liquid parti­cles suspended in the atmosphere.

§  Aftershocks  -  Smaller earthquakes that follow the main earthquake

§  Air - A mixture of many discrete gases, of which nitrogen and oxygen are most abundant, in which varying quantities of tiny solid and liquid particles are suspended.

§  Air mass - A large body of air that is characterized by a sameness of tem­perature and humidity.

§  Air-mass weather - The conditions ex­perienced in an area as an air mass passes over it. Because air masses are large and fairly homogenous, air-mass weather will be fairly constant and may last for several days.

§  Air pollutants -  Airborne particles and gases that occur in concentrations that endanger the health and well-being of organisms or disrupt the orderly func­tioning of the environment.

§  Air pressure - The force exerted by the weight of a column of air above a given point.

§  Albedo - The reflectivity of a sub­stance, usually expressed as a percent­age of the incident radiation reflected.

§  Alluvial fan - A fan-shaped deposit of sediment formed when a stream's slope is abruptly reduced.

§  Alluvium -  Unconsolidated sediment deposited by a stream.

§  Alpine glacier - A glacier confined to a mountain valley, which in most in­stances had previously been a stream valley.

§  Altitude (of the Sun) - The angle of the Sun above the horizon.

§  Andesitic composition - See Interme­diate composition.

§  Anemometer - An instrument used to determine wind speed.

§  Aneroid barometer - An instrument for measuring air pressure that con­sists of evacuated metal chambers very sensitive to variations in air pressure.

§  Angle of repose - The steepest angle at which loose material remains sta­tionary without sliding downslope.

§  Angular unconformity - An unconfor­mity in which the strata below dip at an angle different from that of the beds above.

§  Annual mean temperature - An aver­age of the 12 monthly temperature means.

§  Annual temperature - The dif­ference between the highest and low­est monthly temperature means.

§  Annual temperature range -  

§  Antarctic Circle – The parallel of latitude at 66½° S.  It is the furthest latitude away from (north of) the South Pole that will receive 24 hours of Sunlight on the winter solstice (December 21).

§  Anthracite -  A hard, metamorphic form of coal that burns clean and hot

§  Anticline  -  A fold in sedimentary stra­ta resembling an arch

§  Anticyclone - A high-pressure center characterized by a clockwise flow of air in the Northern Hemisphere.

§  Aphelion - The place in the orbit of a planet where the planet is farthest from the Sun.

§  Aphotic zone - That portion of the ocean where there is no sunlight.

§  Apparent magnitude - The brightness of a star when viewed from Earth.

§  Aquifer -   Rock or soil through which groundwater moves easily

§  Aquitard - Impermeable beds that hin­der or prevent groundwater move­ment.

§   Archean eon -  The second eon of Pre­cambrian time, following the Hadean and preceding the Proterozoic. It ex­tends between 3.8 billion and 2.5 bil­lion years before the present.

§  Arête - A narrow knifelike ridge sepa­rating two adjacent glaciated valleys.

§  Arid - See Desert.

§  Arid climate - See Dry climate.

§  Arkose -  A feldspar-rich sandstone.

§  Artesian well  -  A well in which the water rises above the level where it was initially encountered.

§  Arctic Circle -  The parallel of latitude at 66½° N.  It is the furthest latitude away from (south of) the North Pole that will receive 24 hours of Sunlight on the summer solstice (June 21).

§  Asteroids - Thousands of small planet like bodies, ranging in size from a few hundred kilometers to less than a kilometer, whose orbits lie mainly be­tween those of Mars and Jupiter.

§  Asthenosphere -  A subdivision of the mantle situated below the lithosphere. This zone of weak material exists below a depth of about 100 kilometers and in some regions extends as deep as 700 kilometers. The rock within this zone is easily deformed.

§  Astronomical theory - A theory of cli­matic change first developed by the Yugoslavian astronomer Milankovitch. It is based upon changes in the shape of Earth's orbit, variations in the obliq­uity of Earth's axis, and the wobbling of Earth's axis.

§  Astronomical Unit (AU) - Average dis­tance from Earth to the Sun; 1.5 X 108 km, or 93 x 106 miles.

§  Astronomy - The scientific study of the universe; it includes the observa­tion and interpretation of celestial bod­ies and phenomena.

§  Atmosphere - The gaseous portion of a planet; the planet's envelope of air. One of the traditional subdivisions of Earth's physical environment.

§  Atmospheric instability – Exists when the environmental lapse rate is greater than the dry adiabatic rate.  This can occur when the air above is very cold.

§  Atoll -  A continuous or broken ring of coral reef surrounding a central lagoon.

§  Atom -  The smallest particle that ex­ists as an element

§  Atomic mass unit – A proton or neutron has a mass just slightly more than one atomic mass unit, whereas an electron is only about on two-thousandth of an atomic mass unit. (pg 34 of Earth Science 11e)

§  Atomic number  -  The number of pro­tons in the nucleus of an atom

§  Atomic weight -  The average of the atomic masses of isotopes for a given element

§  Aurora -  A bright display of ever-changing light caused by solar radia­tion interacting with the upper atmosphere in the region of the poles.

§  Autumnal equinox -  The equinox that occurs on September 21-23 in the Northern Hemisphere and on March 21-22 in the Southern Hemisphere.

§  Backshore - The inner portion of the shore, lying landward of the high-tide shoreline. It is usually dry, being af­fected by waves only during storms.

§  Backswamp - A poorly drained area on a floodplain that results when natu­ral levees are present.

§  Bar - Common term for sand and gravel deposits in a stream channel.

§  Barchan dune - A solitary sand dune shaped like a crescent with its tips pointing downward.

§  Barchanoid dune - Dunes forming scalloped rows of sand oriented at right angles to the wind. This form is intermediate between isolated barchans and extensive waves of trans­verse dunes.

§  Barograph - A recording barometer.

§  Barometer - An instrument that meas­ures atmospheric pressure.

§  Barometric tendency - See Pressure tendency.

§  Barred spiral - A galaxy having straight arms extending from its nucleus.

§  Barrier island - A low, elongate ridge of sand that parallels the coast.

§  Barrier reefA long, narrow ridge of coral or rock parallel to and relatively near a coastline, separated from the coastline by a lagoon too deep for coral growth.

§  Basalt - A fine-grained igneous rock of mafic composition.

§  Basaltic composition -  A composi­tional group of igneous rocks indicat­ing that the rock contains substantial dark silicate minerals and calcium-rich plagioclase feldspar.

§  Base level - The level below which a stream cannot erode.

§  Basin - A circular downfolded structure.

§  Batholith - A large mass of igneous rock that formed when magma was emplaced at depth, crystallized, and subsequently exposed by erosion.

§  Bathymetry - The measurement of ocean depths and the charting of the shape or topography of the ocean floor.

§  Baymouth bar - A sandbar that com­pletely crosses a bay, sealing it off from the open ocean.

§  Beach - An accumulation of sediment found along the landward margin of the ocean or a lake.

§  Beach drift -  The transport of sedi­ment in a zigzag pattern along a beach caused by the uprush of water from obliquely breaking waves.

§  Beach face - The wet, sloping surface that extends from the berm to the shoreline.

§  Beach nourishment - The process by which large quantities of sand are added to the beach system to offset losses caused by wave erosion.

§  Bed load - Sediment that is carried by a stream along the bottom of its channel.

§  Benioff zone - Zone of inclined seis­mic activity that extends from a trench downward into the asthenosphere.

§  Benthic zone - The marine life zone that includes any sea bottom surface re­gardless of its distance from shore.

§  Benthos - The forms of marine life that live on or in the ocean bottom.

§  Bergeron process - A theory that re­lates the formation of precipitation to supercooled clouds, freezing nuclei, and the different saturation levels of ice and liquid water.

§  Berm - The dry, gently sloping zone on the backshore of a beach at the foot of the coastal cliffs or dunes.

§  Big Bang Theory - The theory that proposes that the universe originated as a single mass, which subsequently exploded.

§   Binary stars - Two stars revolving around a common center of mass under their mutual gravitational attraction.

§  Biogenous sediment - Seafloor sedi­ments consisting of material of marine-organic origin.

§  Biomass -  The total mass of a defined organism or group of organisms in a particular area or ecosystem.

§  Biosphere - The totality of life on Earth; the parts of the solid Earth, hy­drosphere, and atmosphere in which living organisms can be found.

§  Bituminous -  The most common form of coal, often called soft, black coal.

§  Black dwarf -  A final state of evolu­tion for a star, in which all of its energy sources are exhausted and it no longer emits radiation.

§  Black hole -  A massive star that has collapsed to such a small volume that its gravity prevents the escape of all radiation.

§  Blowout (deflation hollow) -  A de­pression excavated by the wind in eas­ily eroded deposits.

§  Bode's law  -  A sequence of numbers that approximates the mean distances of the planets from the Sun.

§  Body waves  -  Seismic waves that trav­el through Earth's interior.

§  Bowen's reaction series  -  A concept proposed by N. L. Bowen that illus­trates the relationships between magma and the minerals crystallizing from it during the formation of ig­neous rocks.

§  Braided stream -  A stream consisting of numerous intertwining channels

§  Breakwater  -  A structure protecting a nearshore area from breaking waves.

§  Breccia -  A sedimentary rock com­posed of angular fragments that were lithified.

§  Bright-line spectrum -  The bright lines produced by an incandescent gas under low pressure.

§  Bright nebula -  A cloud of glowing gas excited by ultraviolet radiation from hot stars.

§  Brittle failure (deformation) -  Defor­mation that involves the fracturing of rock. Associated with rocks near the surface.

§  Cactolith -  A quasi-horizontal chonolith composed of anastomosing ductoliths, whose distal ends curl like a harpolith, thin like a sphenolith, or bulge discor­dantly like an akmolith or ethmolith.

§  Caldera -  A large depression typically caused by collapse or ejection of the summit area of a volcano.

§  Calorie -  The amount of heat required to raise the temperature of one gram of water 1°C.

§  alving  -  Wastage of a glacier that oc­curs when large pieces of ice break off into water.

§  Capacity  -  The total amount of sedi­ment a stream is able to transport

§  Carbonate group -  Mineral group whose members contain the carbonate ion (CO2-2) and one or more kinds of positive ions. Calcite is a common ex­ample.

§   Cassini division -  A wide gap in the ring system of Saturn between the A ring and the B ring.

§   Catastrophism -  The concept that Earth was shaped by catastrophic events of a short-term nature.

§   Cavern -  A naturally formed under­ground chamber or series of chambers most commonly produced by solution activity in limestone.

§   Celestial sphere  -  An imaginary hol­low sphere upon which the ancients believed the stars were hung and car­ried around Earth.

§   Cenozoic era -  A span on the geologic time scale beginning about 65 million years ago following the Mesozoic era.

§   Cepheid variable  -  A star whose brightness varies periodically because it expands and contracts. A type of pulsating star.

§  CFC’s – Short for chlorofluorocarbons.  These are the compounds thought to be responsible for depleting the Earth’s ozone layer.  They were used for air conditioning, cleaning solvents, propellants for aerosol sprays, etc.

§  Chemical sedimentary rock -  Sedimentary rock consisting of materi­al that was precipitated from water by either inorganic or organic means.

§   Chemical weathering -  The processes by which the internal structure of a mineral is altered by the removal and/or addition of elements.

§   Chinook -   -  A wind blowing down the leeward side of a mountain and warm­ing by compression.

§   Chromatic aberration -  The property of a lens whereby light of different col­ors is focused at different places.

§   Chromosphere -  The first layer of the solar atmosphere found directly above the photosphere.

§   Cinder cone -  A rather small volcano built primarily of pyroclastics ejected from a single vent.

§  Circle of illumination -  The great circle that separates daylight from darkness.

§  Cirque -  An amphitheater-shaped basin at the head of a glaciated valley pro­duced by frost wedging and plucking.

§  Cirrus -  One of three basic cloud forms; also one of the three high cloud types. They are thin, delicate ice-crys­tal clouds often appearing as veil-like patches or thin, wispy fibers.

§  Clastic rock -  A sedimentary rock made of broken fragments of preexist­ing rock.

§   Cleavage -  The tendency of a mineral to break along planes of weak bonding.

§  Climate  -  A description of aggregate weather conditions; the sum of all sta­tistical weather information that helps describe a place or region.

§   Climate system -  The exchanges of energy and moisture that occur among the atmosphere, hydrosphere, solid Earth, biosphere, and cryosphere.

§  Climate-feedback mechanism -  Because the atmosphere is a complex interactive physical system, several different possible outcomes may result when one of the system's elements is altered. These various possibilities are called climate feedback mechanisms

§  Climatology -  The scientific study of climate.

§  Closed system -  A system that is self contained with regards to matter—that is, no matter enters or leaves.

§  Cloud -  A form of condensation best described as a dense concentration of suspended water droplets or tiny ice crystals.

§  Clouds of vertical development -  A cloud that has its base in the low-height range but extends upward into the middle or high altitudes.

§  Cluster (star) -  A large group of stars.

§  Coarse-grained texture -  An igneous rock texture in which the crystals are roughly equal in size and large enougl so that individual minerals can be identified with the unaided eye

§  Coast -  A strip of land that extends in­land from the coastline as far as ocean-related features can be found.

§  Coastline -  The coast's seaward edge. The landward limit of the effect of the highest storm waves on the shore.

§  Col -  A pass between mountain val­leys where the headwalls of two cirques intersect.

§  Cold front -  A front along which a cold air mass thrusts beneath a warmer air mass.

§  Collision-coalescence process -  A theory of raindrop formation in warm clouds (above 0°C) in which large cloud droplets (giants) collide and join together with smaller droplets to form a raindrop. Opposite electrical charges may bind the cloud droplets together.

§  Column -  A feature found in caves that is formed when a stalactite and stalag­mite join.

§  Columnar joints -  A pattern of cracks that form during cooling of molten rock to generate columns that are gen­erally six-sided.

§  Coma -  The fuzzy, gaseous component of a comet's head.

§  Comet -  A small body that generally revolves about the Sun in an elongated orbit.

§  Competence -  A measure of the largest particle a stream can transport; a factor dependent on velocity.

§  Composite cone -  Composite cone A volcano com­posed of both lava flows and pyroclas­tic material.

§  Compound -  A substance formed by the chemical combination of two or more elements in definite proportions and usually having properties different from those of its constituent elements.

§  Condensation -  The change of state from a gas to a liquid.

§  Condensation nuclei -  Tiny bits of particulate matter that serve as sur­faces on which water vapor condenses.

§  Conditional instability -  Moist air with a lapse rate between the dry and wet adiabatic rates.

§  Conduction -  The transfer of heat through matter by molecular activity. Energy is transferred through colli­sions from one molecule to another.

§  Conduit -  A pipe-like opening through which magma moves toward Earth's surface. It terminates at a surface open­ing called a vent.

§  Cone of depression -  A cone-shaped depression in the water table immedi­ately surrounding a well.

§  Conformable -  Layers of rock that were deposited without interruption.

§  Conglomerate -  A sedimentary rock composed of rounded gravel-size particles.

§  Constellation -  An apparent group of stars originally named for mythical characters. The sky is presently divid­ed into 88 constellations.

§  Contact metamorphism -  Changes in rock caused by the heat from a nearby magma body.

§  Continental (c)  air mass  - An air mass that forms over land; it is normally rel­atively dry.

§  Continental drift theory -  A theory that originally proposed that the conti­nents are rafted about. It has essential­ly been replaced by the plate tectonics theory.

§  Continental margin -  That portion of the seafloor adjacent to the continents. It may include the continental shelf, continental slope, and continental rise.

§  Continental rise -  The gently sloping surface at the base of the continental slope.

§  Continental shelf -  The gently sloping submerged portion of the continental margin, extending from the shoreline to the continental slope.

§  Continental slope -  The steep gradi­ent that leads to the deep-ocean floor and marks the seaward edge of the continental shelf.

§  Continental volcanic arc -  Mountains formed in part by igneous activity as­sociated with the subduction of ocean­ic lithosphere beneath a continent.

§  Continuous spectrum -  An uninter­rupted band of light emitted by an in­candescent solid, liquid, or gas under pressure.

§  Convection -  The transfer of heat by the movement of a mass or substance. It can take place only in fluids.

§  Convergence -  The condition that ex­ists when the distribution of winds within a given area results in a net hor­izontal inflow of air into the area. Be­cause convergence at lower levels is associated with an upward movement of air, areas of convergent winds are regions favorable to cloud formation and precipitation.

§  Convergent plate boundary -  A boundary in which two plates move together, causing one of the slabs of lithosphere to be consumed into the mantle as it descends beneath on an overriding plate.

§  Coral reef -  Structure formed in a warm, shallow, sunlit ocean environ­ment that consists primarily of the cal­cite-rich remains of corals as well as the limy secretions of algae and the hard parts of many other small organisms.

§  Core - Located beneath the mantle, it is the innermost layer of Earth. The core is divided into an outer core and an inner core.

§  Coriolis force (effect) -  The deflective force of Earth's rotation on all free-moving objects, including the atmos­phere and oceans. Deflection is to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.

§  Corona -  The outer, tenuous layer of the solar atmosphere.

§  Correlation -  Establishing the equiva­lence of rocks of similar age in differ­ent areas.

§  Covalent bond -  A chemical bond produced by the sharing of electrons.

§  Crater -  The depression at the summit of a volcano, or that which is produced by a meteorite impact.

§  Creep -  The slow downhill movement of soil and regolith.

§  Crevasse -  A deep crack in the brittle surface of a glacier.

§  Cross-bedding -  Structure in which relatively thin layers are inclined at an angle to the main bedding. Formed by currents of wind or water.

§  Cross-cutting -  A principle of relative dating. A rock or fault is younger than any rock (or fault) through which it cuts.

§  Crust -  The very thin outermost layer of Earth.

§  Crystal -  An orderly arrangement of atoms.

§  Crystal form -  The external appear­ance of a mineral as determined by its internal arrangement of atoms. Crystallization

§  Crystallization -  The formation and growth of a crystalline solid from a liq­uid or gas.

§  Crystal settling -  During the crystal­lization of magma, the earlier-formed minerals are denser than the liquid portion and settle to the bottom of the magma chamber.

§  Cumulus One of three basic cloud forms; also the name given one of the clouds of vertical development. Cumu­lus are billowy individual cloud mass­es that often have flat bases.-  

§  Cup anemometer  -  See Anemometer.

§  Curie point -  The temperature above which a material loses its magneti­zation.

§  Cutoff -  A short channel segment created when a river erodes through the narrow neck of land between meanders.

§  Cyclone -  A low-pressure center char­acterized by a counterclockwise flow of air in the Northern Hemisphere.

§  Daily mean -  The mean temperature for a day that is determined by averag­ing the 24 hourly readings or, more commonly, by averaging the maximum and minimum temperatures for a day.

§  Daily temperature range -  The differ­ence between the maximum and mini­mum temperatures for a day.

§  Dark-line spectrum  -  See Absorption spectrum.

§  Dark nebula -  A cloud of interstellar dust that obscures the light of more distant stars and appears as an opaque curtain.

§  Daughter product -  An isotope result­ing from radioactive decay.

§  Debris flow -  A relatively rapid type of mass wasting that involves a flow of soil and regolith containing a large amount of water. Also called mudflows.

§  Declination (stellar) -  The angular dis­tance north or south of the celestial equator denoting the position of a ce­lestial body.

§  Decompression melting -  Melting that occurs as rock ascends due to a drop in confining pressure.

§  Deep-ocean basin -  The portion of seafloor that lies between the continen­tal margin and the oceanic ridge sys­tem. This region comprises almost 30 percent of Earth's surface.

§  Deep-ocean trench  -  See Trench.

§  Deep-sea fan -  A cone-shaped deposit at the base of the continental slope. The sediment is transported to the fan by turbidity currents that follow sub­marine canyons.

§  Deflation -  The lifting and removal of loose material by wind.

§  Deformation -  General term for the processes of folding, faulting, shearing, compression, or extension of rocks as the result of various natural forces.

§  Delta -  An accumulation of sediment formed where a stream enters a lake or ocean.

§  Dendritic pattern -  A stream system that resembles the pattern of a branch­ing tree.

§  Density -  Mass per unit volume of a substance, usually expressed as grams per cubic centimeter (g/cm3).

§  Deposition -  The process by which water vapor is changed directly to a solid without passing through the liq­uid state.

§  Desalination -  The removal of salts and other chemicals from seawater.

§  Desert -  One of the two types of dry climate; the driest of the dry climates.

§  Desert pavement -  A layer of coarse pebbles and gravel created when wind removed the finer material.

§  Detrital sedimentary rock -  Rock formed from the accumulation of ma­terial that originated and was trans­ported in the form of solid particles derived from both mechanical and chemical weathering.

§  Dew-point temperature -  The tem­perature to which air has to be cooled in order to reach saturation.

§  Differential weathering -  The variation in the rate and degree of weathering caused by such factors as mineral make­up, degree of jointing, and climate.

§  Diffused light -  Solar energy scattered and reflected in the atmosphere that reaches Earth's surface in the form of diffuse blue light from the sky.

§  Dike -  A tabular-shaped intrusive ig­neous feature that cuts through the surrounding rock.

§  Dip-slip fault -  A fault in which the movement is parallel to the dip of the fault.

§  Discharge -  The quantity of water in a stream that passes a given point in a period of time.

§  Disconformity -  A type of unconfor­mity in which the beds above and below are parallel.

§  Disseminated deposit – Any econom­ic mineral deposit in which the desired mineral occurs as scattered particles in the rock but in sufficient quantity to make the deposit an ore.

§  Dissolved load -  That portion of a stream's load carried in solution.

§  Distributary -  A section of a stream that leaves the main flow.

§  Diurnal tidal pattern -  A tidal pattern exhibiting one high tide and one low tide during a tidal day; a daily tide.

§  Divergence -  The condition that exists when the distribution of winds within a given area results in a net horizontal outflow of air from the region. In di­vergence at lower levels the resulting deficit is compensated for by a down­ward movement of air from aloft; hence, areas of divergent winds are unfavorable to cloud formation and precipitation.

§  Divergent plate boundary -  A region where the rigid plates are moving apart, typified by the mid-oceanic ridges.

§  Divide -  An imaginary line that sepa­rates the drainage of two streams; often found along a ridge.

§  Dome -  A roughly circular upfolded structure similar to an anticline.

§  Doppler effect -  The apparent change in wavelength of radiation caused by the relative motions of the source and the observer.

§  Doppler radar -  In addition to the tasks performed by conventional radar, this new generation of weather radar can detect motion directly and hence greatly improve tornado and se­vere storm warnings.

§  Drainage basin -  The land area that contributes water to a stream

§  Drawdown -  The difference in height between the bottom of a cone of de­pression and the original height of the water table.

§  Drift  -  see Glacial drift.

§  Drumlin -  A streamlined asymmetrical hill composed of glacial till. The steep side of the hill faces the direction from which the ice advanced.

§  Dry adiabatic rate -  The rate of adia­batic cooling or warming in unsaturat­ed air. The rate of temperature change is 1°C per 100 meters.

§  Dry climate -  A climate in which year­ly precipitation is not as great as the potential loss of water by evaporation

§  Dry-summer subtropical climate -  A climate located on the west sides of continents between latitudes 300 and 45°. It is the only humid climate with a strong winter precipitation maximum.

§  Ductile deformation -  A type of solid state flow that produces a change in the size and shape of a rock body with­out fracturing. Occurs at depths where temperatures and confining pressures are high.

§  Dune -  A hill or ridge of wind-deposited sand.

§  Earthflow -  The downslope move­ment of water-saturated, clay-rich sed­iment. Most characteristic of humid regions.

§  Earthquake -  The vibration of Earth produced by the rapid release of energy.

§  Earth science -  The name for all the sciences that collectively seek to un­derstand Earth. It includes geology, oceanography, meteorology, and as­tronomy.

§  Earth system science -  An interdisci­plinary study that seeks to examine Earth as a system composed of numer­ous interacting parts or subsystems.

§  Ebb current -  The movement of a tidal current away from the shore.

§  Eccentricity -  The variation of an el­lipse from a circle.

§  Echo sounder -  An instrument used to determine the depth of water by measuring the time interval between emission of a sound signal and the re­turn of its echo from the bottom.

§  Eclipse -  The cutting off of the light of one celestial body by another passing in front of it.

§  Ecliptic -  The yearly path of the Sun plotted against the background of stars.

§  Elastic rebound -  The sudden release of stored strain in rocks that results in movement along a fault.

§  Electromagnetic radiation -  See Ra­diation.

§  Electromagnetic spectrum -  The dis­tribution of electromagnetic radiation by wavelength.

§  Electron -  A negatively charged sub­atomic particle that has a negligible mass and is found outside an atom's nucleus. A proton or neutron has a mass just slightly more than one atomic mass unit, whereas an electron is only about on two-thousandth of an atomic mass unit. (pg 34, Earth Science 11e)

§  Element -  A substance that cannot be decomposed into simpler substances by ordinary chemical or physical means.

§  Elements of weather and climate -  Those quantities or properties of the atmosphere that are measured regular­ly and that are used to express the na­ture of weather and climate.

§  Elliptical galaxy -  A galaxy that is round or elliptical in outline. It con­tains little gas and dust, no disk or spiral arms, and few hot, bright stars.

§  El Nino -  The name given to the peri­odic warming of the ocean that occurs in the central and eastern Pacific. A major El Nino episode can cause ex­treme weather in many parts of the world.

§  Eluviation -  The washing out of fine soil components from the A horizon by downward-percolating water

§  Emergent coast -  A coast where land that was formerly below sea level has been exposed either because of crustal uplift or a drop in sea level or both.

§  Emission nebula -  A gaseous nebula that derives its visible light from the fluorescence of ultraviolet light from a star in or near the nebula.

§  End moraine -  A ridge of till mark­ing a former position of the front of a glacier.

§  Energy -  The capacity to do work.

§  Energy levels -  Spherically shaped negatively charged zones that sur­round the nucleus of an atom.

§  Environment -  Everything that sur­rounds and influences an organism. Environmental lapse rate The rate of temperature decrease with increas­ing height in the troposphere.

§  Environmental lapse rate – (see also “lapse rate”) The actual (observed as opposed to calculated) decrease in temperature with an increase in altitude through the troposphere. 

§  Eon -  The largest time unit on the geo­logic time scale, next in order of mag­nitude above era.

§  Ephemeral stream - A stream that is usually dry because it carries water only in response to specific episodes of rainfall. Most desert streams are of this type.

§  Epicenter -   The location on Earth's surface that lies directly above the focus of an earthquake.

§  Epoch -  A unit of the geologic calen­dar that is a subdivision of a period.

§  Equatorial low -  A belt of low pres­sure lying near the equator and be­tween the subtropical highs.

§  Equatorial system -  A method of lo­cating stellar objects much like the co­ordinate system used on Earth's surface.

§  Equinox -  The time when the vertical rays of the Sun are striking the equa­tor. The length of daylight and dark­ness is equal at all latitudes at equinox.

§  Era -  A major division on the geologic calendar; eras are divided into shorter units called periods.

§  Erosion -  The incorporation and trans­portation of material by a mobile agent, such as water, wind, or ice.

§  Eruptive variable - A star that varies in brightness.

§  Escape velocity - The initial velocity an object needs to escape from the sur­face of a celestial body.

§  Esker -  Sinuous ridge composed large­ly of sand and gravel deposited by a stream flowing in a tunnel beneath a glacier near its terminus.

§  Estuary -  A partially enclosed coastal water body that is connected to the ocean. Salinity here is measurably re­duced by the freshwater flow of rivers.

§  Euphotic zone -  The portion of the photic zone near the surface, where light is bright enough for photosynthe­sis to occur.

§  Evaporation -  The process of convert­ing a liquid to a gas.

§  Evaporite -  A sedimentary rock formed of material deposited from so­lution by evaporation of the water.

§  Evapotranspiration -  The combined effect of evaporation and transpiration.

§  Evolution, (Theory of) -  A fundamen­tal theory in biology and paleontology that sets forth the process by which members of a population of organisms come to differ from their ancestors. Or­ganisms evolve by means of muta­tions, natural selection, and genetic factors. Modern species are descended from related but different species that lived in earlier times.

§  Exfoliation dome -  Large, dome-shaped structure, usually composed of granite, formed by sheeting.

§  Exotic stream -  A permanent stream that traverses a desert and has its source in well-watered areas outside the desert.

§  External process -  Process such as weathering, mass wasting or erosion that is powered by the Sun and trans­forms solid rock into sediment.

§  Extrusive -  Igneous activity that oc­curs outside the crust.

§  Eye -  A zone of scattered clouds and calm averaging about 20 kilometers in diameter at the center of a hurricane.

§  Eyepiece -  A short-focal-length lens used to enlarge the image in a tele­scope. The lens nearest the eye.

§  Eye wall -  The doughnut-shaped area of intense cumulonimbus develop­ment and very strong winds that sur­rounds the eye of a hurricane.

§  Fall -  A type of movement common to mass-wasting processes that refers to the free falling of detached individual pieces of any size.

§  Fault -  A break in a rock mass along which movement has occurred.

§  Fault-block mountain -  A mountain formed by the displacement of rock along a fault.

§  Fault creep -  Displacement along a fault that is so slow and gradual that little seismic activity occurs.

§  Fault scarp -  A cliff created by movement along a fault. It represents the exposed surface of the fault prior to modification by weathering and erosion.

§  Felsic -  The group of igneous rocks composed primarily of feldspar and quartz.

§  Fetch -  The distance that the wind has traveled across the open water. Filaments Dark, thin streaks that ap­pear across the bright solar disk.

§  Fine-grained texture – A texture of igneous rocks in which the crystals are too small for individual minerals to be distinguished with the unaided eye.

§  Fiord -  A steep-sided inlet of the sea formed when a glacial trough was par­tially submerged.

§  Fissure eruption -  An eruption in which lava is extruded from narrow fractures or cracks in the crust.

§  Flare -  A sudden brightening of an area on the Sun.

§  Flood basalts -  Flows of basaltic lava that issue from numerous cracks or fis­sures and commonly cover extensive areas to thicknesses of hundreds of meters.

§  Flood current -  The tidal current asso­ciated with the increase in the height of the tide.

§  Floodplain -  The flat, low-lying por­tion of a stream valley subject to peri­odic inundation.

§  Flow -  A type of movement common to mass-wasting processes in which water-saturated material moves downslope as a viscous fluid.

§  Fluorescence -  The absorption of ul­traviolet light, which is reemitted as visible light.

§  Focal length -  The distance from the lens to the point where it focuses par­allel rays of light.

§  Focus (earthquake) -  The zone within Earth where rock displacement pro­duces an earthquake.

§  Focus (light) -  The point where a lens or mirror causes light rays to converge

§  Fog -  A cloud with its base at or very near Earth's surface.

§  Fold -  A bent rock layer or series of layers that were originally horizontal and subsequently deformed.

§  Foliated -  A texture of metamorphic rocks that gives the rock a layered ap­pearance.

§  Food chain -  A succession of organ­isms in an ecological community through which food energy is trans­ferred from producers through herbi­vores and on to one or more carnivores.

§  Food web -  A group of interrelated food chains.

§  Foreshocks -  Small earthquakes that often precede a major earthquake.

§  Foreshore -  That portion of the shore lying between the normal high and low water marks; the intertidal zone.

§  Fossil fuel -  General term for any hy­drocarbon that may be used as a fuel, including coal, oil, and natural gas.

§  Fossils -  The remains or traces of or­ganisms preserved from the geologic past.

§  Fossil succession -  Fossil organisms that succeed one another in a definite and determinable order, and any time period can be recognized by its fossil content.

§  Fracture -  Any break or rupture in rock along which no appreciable movement has taken place.

§  Freezing -  The change of state from a liquid to a solid.

§  Freezing nuclei -  Solid particles that serve as cores for the formation of ice crystals.

§  Fringing reefA coral reef formed close to the shoreline of an island or continent. Fringing reefs usually have a rough, table-like surface that is exposed during low tide and a steep edge sloping toward the open water.

§  Front -  The boundary between two adjoining air masses having contrast­ing characteristics.

§  Frontal fog -  Fog formed when rain evaporates as it falls through a layer of cool air.

§  Frontal wedging -  Lifting of air re­sulting when cool air acts as a barrier over which warmer, lighter air will rise.

§  Frost wedging -  The mechanical breakup of rock caused by the expan­sion of freezing water in cracks and crevices.

§  Fumarole -  A vent in a volcanic area from which fumes or gases escape.

§  Galactic cluster -  A system of galaxies containing from several to thousands of member galaxies.

§  Geocentric -  The concept of an Earth-centered universe.

§  Geologic time scale -  The division of Earth history into blocks of time—eons, eras, periods, and epochs. The time scale was created using relative dating principles.

§  Geology -  The science that examines Earth, its form and composition, and the changes it has undergone and is undergoing.

§  Geosphere -  The solid Earth, the largest of Earth's four major spheres.

§  Geostrophic wind -  A wind, usually above a height of 600 meters (2000 feet), that blows parallel to the isobars. Geothermal energy Natural steam used for power generation.

§  Geothermal gradient -  The gradual increase in temperature with depth in the crust. The average is 30°C per kilo­meter in the upper crust.

§  Geyser -  A fountain of hot water eject­ed periodically.

§  Giant (star) -  A luminous star of large radius.

§  Glacial drift -  An all-embracing term for sediments of glacial origin, no mat­ter how, where, or in what shape they were deposited.

§  Glacial erratic -  An ice-transported boulder that was not derived from bedrock near its present site.

§  Glacial striations -  Scratches and grooves on bedrock caused by glacial abrasion.

§  Glacial trough -  A mountain valley that has been widened, deepened, and straightened by a glacier.

§  Glacier -  A thick mass of ice originat­ing on land from the compaction and recrystallization of snow that shows evidence of past or present flow.

§  Glassy -  A term used to describe the texture of certain igneous rocks, such as obsidian, that contain no crystals.

§  Glaze -  A coating of ice on objects formed when supercooled rain freezes on contact.

§  Globular cluster -  A nearly spherically shaped group of densely packed stars.

§  Globule - A dense, dark nebula thought to be the birthplace of stars.

§  Gondwanaland -  The southern por­tion of Pangaea consisting of South America, Africa, Australia, India, and Antarctica

§  Graben -  A valley formed by the downward displacement of a fault‑bounded block.

§  Graded bed -  A sediment layer that is characterized by a decrease in sedi­ment size from bottom to top.

§  Gradient -  The slope of a stream; gen­erally measured in feet per mile.

§  Granitic composition A composi­tional group of igneous rocks that indi­cates a rock is composed almost entirely of light-colored silicates.

§  Granules - The fine structure visible on the solar surface caused by convec­tive cells below.

§  Gravitational collapse - The gradual subsidence of mountains caused by lateral spreading of weak material lo­cated deep within these structures. -  

§  Greenhouse effect - The transmission of short-wave solar radiation by the at­mosphere, coupled with the selective absorption of longer-wavelength ter­restrial radiation, especially by water vapor and carbon dioxide.

§  Groin - A short wall built at a right angle to the shore to trap moving sand.

§  Ground moraine - An undulating layer of till deposited as the ice front retreats.

§  Groundwater -  Water in the zone of saturation

§  Guyot - A submerged flat-topped seamount.

§  Gyre - The large circular surface cur­rent pattern found in each ocean.

§  Habit – I think this is geology talk for the crystal shape of a mineral.

§  Hadean eon - The first eon on the ge­ologic time scale; this eon ended 3.8 billion years ago and preceded the Archean eon.

§  Hail - Nearly spherical ice pellets hav­ing concentric layers and formed by the successive freezing of layers of water.

§  Half-life - The time required for one half of the atoms of a radioactive sub­stance to decay.

§  Halocline - A layer of water in which there is a high rate of change in salinity in the vertical dimension.

§  Hanging valley - A tributary valley that enters a glacial trough at a consid­erable height above its floor.

§  Hardness - The resistance a mineral offers to scratching.

§  Hard stabilization - Any form of arti­ficial structure built to protect a coast or to prevent the movement of sand along a beach. Examples include groins, jetties, breakwaters, and sea­walls.

§  Heliocentric - The view that the Sun is at the center of the solar system.

§  Heat - The kinetic energy of random molecular motion.

§  Hertzsprung-Russell diagram See H-R diagram.

§  High - A center of high pressure char­acterized by anticyclonic winds.

§  High cloud - A cloud that normally has its base above 6000 meters; the base may be lower in winter and at high-latitude locations.

§  Highland climate - Complex pattern of climate conditions associated with mountains. Highland climates are characterized by large differences that occur over short distances.

§  Hogback - A narrow, sharp-crested ridge formed by the upturned edge of a steeply dipping bed of resistant rock.

§  Horizon - A layer in a soil profile.

§  Horn -  A pyramid-like peak formed by glacial action in three or more cirques surrounding a mountain summit

§  Horst - An elongate, uplifted block of crust bounded by faults.

§  Hot spot - A concentration of heat in the mantle capable of producing magma, which in turn extrudes onto Earth's surface. The intraplate volcan­ism that produced the Hawaiian Is­lands is one example.

§  Hot spring - A spring in which the water is 6-9°C (10-15°F) warmer than the mean annual air temperature of its locality.

§  H-R diagram - A plot of stars accord­ing to their absolute magnitudes and spectral types.

§  Hubble's law - Relates the distance to a galaxy and its velocity.

§  Humid continental climate - A rela­tively severe climate characteristic of broad continents in the middle lati­tudes between approximately 40 and 50 degrees north latitude. This climate is not found in the Southern Hemi­sphere, where the middle latitudes are dominated by the oceans.

§  Humidity - A general term referring to water vapor in the air but not to liquid droplets of fog, cloud, or rain.

§  Humid subtropical climate - A climate generally located on the eastern side of a continent and characterized by hot, sultry summers and cool winters.

§  Humus - Organic matter in soil pro­duced by the decomposition of plants and animals.

§  Hurricane - A tropical cyclonic storm having winds in excess of 119 kilome­ters (74 miles) per hour.

§  Hydrogen burning - The conversion of hydrogen through fusion to form helium.

§  Hydrogenous sediment - Seafloor sediments consisting of minerals that crystallize from seawater. An impor­tant example is manganese nodules.

§  Hydrosphere - The water portion of our planet; one of the traditional sub­divisions of Earth's physical en­vironment.

§  Hydrothermal solution - The hot, wa­tery solution that escapes from a mass of magma during the later stages of crystallization. Such solutions may alter the surrounding country rock and are frequently the source of significant ore deposits.

§  Hygrometer - An instrument de­signed to measure relative humidity.

§  Hygroscopic nuclei - Condensation nuclei having a high affinity for water, such as salt particles.

§  Hypothesis - A tentative explanation that is tested to determine if it is valid.

§  Ice cap - Amass of glacial ice covering a high upland or plateau and spread­ing out radially.

§  Ice cap climate - A climate that has no monthly means above freezing and supports no vegetative cover except in a few scattered high mountain areas. This climate, with its perpetual ice and snow, is confined largely to the ice sheets of Greenland and Antarctica.

§  Ice sheet - A very large, thick mass of glacial ice flowing outward in all direc­tions from one or more accumulation centers.

§  Igneous rock - A rock formed by the crystallization of molten magma.

§  Immature soil - A soil lacking horizons.

§  Incised meander - Meandering chan­nel that flows in a steep, narrow valley. They form either when an area is up­lifted or when base level drops.

§  Inclination of the axis - The tilt of Earth's axis from the perpendicular to the plane of Earth's orbit.

§  Inclusion - A piece of one rock unit contained within another. Inclusions are used in relative dating. The rock mass adjacent to the one containing the inclusion must have been there first in order to provide the fragment

§  Index fossil - A fossil that is associated with a particular span of geologic time.

§  Inertia - A property of matter that re­sists a change in its motion.

§  Infiltration - The movement of surface water into rock or soil through cracks and pore spaces.

§  Infrared - Radiation with a wave­length from 0.7 to 200 micrometers.

§  Inner core - The solid innermost layer of Earth, about 1300 kilometers (800 miles) in radius.

§  Inner planets See Terrestrial planets. -  

§  Inselberg - An isolated mountain rem­nant characteristic of the late stage of erosion in an arid region.

§  Intensity (earthquake) - A measure of the degree of earthquake shaking at a given locale based on the amount of damage.

§  Interface - A common boundary where different parts of a system interact (ES11e, pg 23).

§  Interior drainage - A discontinuous pattern of intermittent streams that do not flow to the ocean.

§  Intermediate composition - The com­position of igneous rocks lying be­tween felsic and mafic.

§  Interstellar matter - Dust and gases found between stars.

§  Intertidal zone - The area where land and sea meet and overlap; the zone be­tween high and low tides.

§  Intraplate volcanism - Igneous activi­ty that occurs within a tectonic plate away from plate boundaries.

§  Intrusive rock - Igneous rock that formed below Earth's surface.

§  Ion -  An atom or molecule that pos­sesses an electrical charge.

§  Ionic bond - A chemical bond be­tween two oppositely charged ions formed by the transfer of valence elec­trons from one atom to the other.

§  Ionosphere - A complex zone of ion­ized gases that coincides with the lower portion of the thermosphere.

§  Iron meteorite - One of the three main categories of meteorites. This group is composed largely of iron with varying amounts of nickel (5-20 per­cent). Most meteorite finds are irons.

§  Irregular galaxy -  A galaxy that lacks symmetry

§  Island arc See Volcanic island arc. -  

§  Isobar - A line drawn on a map con­necting points of equal atmospheric pressure, usually corrected to sea level.

§  Isostacy -  The concept that Earth's crust is floating in gravitational bal­ance upon the material of the mantle

§  Isotherms - Lines connecting points of equal temperature.

§  Isotopes - Varieties of the same ele­ment that have different mass numbers; their nuclei contain the same number of protons but different num­bers of neutrons.

§  Jet stream - Swift (120--240 kilometers per hour), high-altitude winds.

§  Jetties - A pair of structures extending into the ocean at the entrance to a har­bor or river that are built for the pur­pose of protecting against storm waves and sediment deposition.

§  Joint - A fracture in rock along which there has been no movement.

§  Jovian planet - The Jupiter-like plan­ets: Jupiter, Saturn, Uranus, and Nep­tune. These planets have relatively low densities.

§  Kame - A steep-sided hill composed of sand and gravel originating when sed­iment is collected in openings in stag­nant glacial ice.

§  Karst -  A topography consisting of nu­merous depressions called sinkholes

§  Kettle holes - Depressions created when blocks of ice became lodged in glacial deposits and subsequently melted.

§  Koppen classification -  A system for classifying climates devised by Wladimir Koppen that is based on mean monthly and annual values of temperature and precipitation.

§  Kuiper belt - A region outside the orbit of Neptune where most short-pe­riod comets are thought to originate.

§  Laccolith - A massive igneous body intruded between preexisting strata.

§  lahar -  Mud flows on the slopes of vol­canoes that result when unstable lay­ers of ash and debris become saturated

§  Lake-effect snow -  Snow showers associated with a cP air mass to which moisture and heat ate added from below as the air mass traverses a large and relatively warm lake (such as on of the Great Lakes), rendering the air mass humid and unstable.

§  Laminar flow - The movement of water particles in straight-line paths that are parallel to the channel. The water particles move downstream without mixing.

§  Land breeze - A local wind blowing from land toward the water during the night in coastal areas.

§  La Niña - An episode of strong trade winds and unusually low sea-surface temperatures in the central and eastern Pacific. The opposite of El Nino.

§  Lapse rate (normal - The average drop in temperature (6.5°C per kilome­ter; 3.5°F per 1000 feet) with increased altitude in the troposphere.

§  Latent heat - The energy absorbed or released during a change in state.

§  Lateral maraine - A ridge of till along the sides of an alpine glacier composed primarily of debris that fell to the gla­cier from the valley walls.

§  Laurasia - The northern portion of Pangaea consisting of North America and Eurasia.

§  Lava - Magma that reaches Earth's surface.

§  Law of conservation of angular momentum -  The product of the veloci­ty of an object around a center of rotation (axis), and the distance squared of the object from the axis is constant.

§  Leaching - The depletion of soluble materials from the upper soil by downward-percolating water.

§  Lightning - A sudden flash of light generated by the flow of electrons be­tween oppositely charged parts of a cumulonimbus cloud or between the cloud and the ground.

§  Light-year - The distance light travels in a year; about 6 trillion miles.

§  Liquefaction - A phenomenon, some­times associated with earthquakes, in which soils and other unconsolidated materials containing abundant water are turned into a fluid-like mass that is not capable of supporting buildings.

§  Lithification - The process, generally cementation and/or compaction, of converting sediments to solid rock.

§  Lithosphere - The rigid outer layer of Earth, including the crust and upper mantle.

§  Local group - The cluster of 20 or so galaxies to which our galaxy belongs.

§  Localized convective lifting - Unequal surface heating that causes lo­calized pockets of air (thermals) to rise because of their buoyancy.

§  Loess - Deposits of windblown silt, lacking visible layers, generally buff-colored, and capable of maintaining a nearly vertical cliff.

§  Longitudinal (seif dunes) - Long ridges of sand oriented parallel to the prevailing wind; these dunes form where sand supplies are limited.

§  Longshore current -  A near-shore cur­rent that flows parallel to the shore

§  Low - A center of low pressure charac­terized by cyclonic winds.

§  Low cloud - A cloud that forms below a height of 2000 meters.

§  Lower mantle - The part of the mantle that extends from the core-mantle boundary to a depth of 660 kilometers.

§  Low-velocity zone - See Asthenosphere.

§  Luminosity - The brightness of a star. The amount of energy radiated by a star.

§  Lunar breccia - A lunar rock formed when angular fragments and dust are welded together by the heat generated by the impact of a meteoroid.

§  Lunar eclipse - An eclipse of the Moon.

§  Lunar highlands - See Terrae.

§  Lunar regolith -  A thin, gray layer on the surface of the Moon, consisting of loosely compacted, fragmented materi­al believed to have been formed by re­peated meteoritic impacts.

§  Luster - The appearance or quality of light reflected from the surface of a mineral.

§  Mafic - Igneous rocks with a low silica content and a high iron-magnesium content.

§  Magma -  A body of molten rock found at depth, including any dissolved gases and crystals.

§  Magmatic differentiation - The process of generating more than one rock type from a single magma.

§  Magnitude (earthquake) - The total amount of energy released during an earthquake.

§  Magnitude (stellar) - A number given to a celestial object to express its rela­tive brightness.

§  Main sequence - A sequence of stars on the Hertzsprung-Russell diagram, containing the majority of stars, that runs diagonally from the upper left to the lower right.

§  Maganese nodules -  Rounded lumps of hydrogenous sediment scat­tered on the ocean floor, consisting mainly of manganese and iron and usually containing small amounts of copper, nickel, and cobalt.

§  Mantle - The 2900-kilometer (1800­mile)-thick layer of Earth located below the crust.

§  Mantle convection - is the slow creeping motion of Earth's rocky mantle in response to perpetual gravitationally unstable variations in its density. This is likely caused by differential heating of mantle material by the core.

§  Mantle plume - A mass of hotter­-than-normal mantle material that as­cends toward the surface, where it may lead to igneous activity. These plumes of solid yet mobile material may originate as deep as the core-mantle boundary.

§  Maria - The Latin name for the smooth areas of the Moon formerly thought to be seas.

§  Marine terrace -  A wave-cut platform that has been exposed above sea level.

§  Marine west coast climate -  A cli­mate found on windward coasts from latitudes 40 to 65 degrees and domi­nated by maritime air masses. Winters are mild, and summers are cool.

§  Maritime (m) air mass -  An air mass that originates over the ocean. These air masses are relatively humid.

§  Mass number - The number of neu­trons and protons in the nucleus of an atom.

§  Mass wasting - The downslope move­ment of rock, regolith, and soil under the direct influence of gravity.

§  Meander - A loop-like bend in the course of a stream.


§  Mean solar day - The average time between two passages of the Sun across the local celestial meridian.

§  Mechanical weathering - The physi­cal disintegration of rock, resulting in smaller fragments.

§  Medial moraine - A ridge of till formed when lateral moraines from two coalescing alpine glaciers join.

§  Melt - The liquid portion of magma, excluding the solid crystals.

§  Melting - The change of state from a solid to a liquid.

§  Mercalli intensity scale See Modi­fied Mercalli intensity scale.

§  Mercury barometer - A mercury-filled glass tube in which the height of the mercury column is a measure of air pressure.

§  Mesocyclone - An intense, rotating wind system in the lower part of a thunderstorm that precedes tornado development.

§  Mesopause - The boundary between the mesosphere and the thermosphere.

§  Mesosphere - The layer of the atmos­phere immediately above the strato­sphere and characterized by decreasing temperatures with height.

§  Mesozoic era - A span on the geologic time scale between the Paleozoic and Cenozoic eras from about 248 million to 65 million years ago.

§  Metamorphic rock - Rocks formed by the alteration of preexisting rock deep within Earth (but still in the solid state) by heat, pressure, and/or chemically active fluids.

§  Metamorphism - The changes in min­eral composition and texture of a rock subjected to high temperature and pressure within Earth.

§  Meteor - The luminous phenomenon observed when a meteoroid enters Earth's atmosphere and burns up; popularly called a "shooting star."

§  Meteorite -  Any portion of a mete­oroid that survives its traverse through Earth's atmosphere and strikes Earth's surface

§  Meteoroid - Small solid particles that have orbits in the solar system.

§  Meteorology - The scientific study of the atmosphere and atmospheric phenomena; the study of weather and climate.

§  Meteor shower - Many meteors ap­pearing in the sky caused when Earth in­tercepts a swarm of meteoritic particles.

§  Middle cloud - A cloud occupying the height range from 2000 to 6000 meters.

§  Middle-latitude cyclone - Large cen­ter of low pressure with an associated cold front and often a warm front. Fre­quently accompanied by abundant precipitation.

§  Mid-ocean ridge See Oceanic ridge.

§  Mineral - A naturally occurring, inor­ganic crystalline material with a unique chemical composition.

§  Mineralogy - The study of minerals.

§  Mineral resource - All discovered and undiscovered deposits of a useful min­eral that can be extracted now or at some time in the future.

§  Mixed tidal pattern - A tidal pattern exhibiting two high tides and two low tides per tidal day with a large in­equality in high water heights, low water heights, or both. Coastal loca­tions that experience such a tidal pat­tern may also show alternating periods of diurnal and semidiurnal tidal pat­terns. Also called mixed semidiurnal.

§  Mixing depth -  The height to which convectional movements extend above Earth's surface. The greater the mixing depth, the better the air quality.

§  Mixing ratio -  The mass of water vapor in a unit mass of dry air; com­monly expressed as grams of water vapor per kilogram of dry air.

§  Model -  A term often used synony­mously with hypothesis but is less pre­cise because it is sometimes used to describe a theory as well.

§  Modified -  Mercalli intensity scale A 12-point scale developed to evaluate earthquake intensity based on the amount of damage to various structures.

§  Mohorovicic discontinuity (Moho) -  The boundary separating the crust from the mantle, discernible by an in­crease in seismic velocity.

§  Mohs scale -  A series of 10 minerals used as a standard in determining hardness.

§  Moment magnitude -  A more precise measure of earthquake magnitude than the Richter scale that is derived from the amount of displacement that occurs along a fault zone.

§  Monocline - A one-limbed flexure in strata. The strata are unusually flat-lying or very gently dipping on both sides of the monocline.

§  Monsoon - Seasonal reversal of wind direction associated with large conti­nents, especially Asia. In winter, the wind blows from land to sea; in sum­mer, from sea to land.

§  Monthly mean temperature - The mean temperature for a month that is calculated by averaging the daily means.

§  Mountain breeze - The nightly downslope winds commonly encoun­tered in mountain valleys.

§  Natural leeves - The elevated land-forms that parallel some streams and act to confine their waters, except dur­ing floodstage.

§  Neap tide - Lowest tidal range, occur­ring near the times of the first- and third-quarter phases of the Moon.

§  Nearshore zone -  The zone of beach that extends from the low-tide shore­line seaward to where waves break at low tide.

§  Nebula - A cloud of interstellar gas and/or dust.

§  Nebular hypothesis -  The basic idea that the Sun and planets formed from the same cloud of gas and dust in in­terstellar space.

§  Nekton - Pelagic organisms that can move independently of ocean currents by swimming or other means of propulsion.

§  Negative feedback mechanism -  A feedback mechanism that tends to maintain a system as it is—that is, maintain the status quo.

§  Neritic zone - The marine-life zone that extends from the low tideline out to the shelf break.

§  Neutron - A subatomic particle found in the nucleus of an atom. The neutron is electrically neutral and has a mass approximately that of a proton.

§  Neutron star - A star of extremely high density composed entirely of neutrons.

§  Nonconformity - An unconformity in which older metamorphic or intrusive igneous rocks are overlain by younger sedimentary strata.

§  Nonfoliated - Metamorphic rocks that do not exhibit foliation.

§  Nonmetallic mineral resource -  Mineral resource that is not a fuel or processed for the metals it contains

§  Nonrenewable resource - Resource that forms or accumulates over such long time spans that it must be consid­ered as fixed in total quantity

§  Normal fault -  A fault in which the rock above the fault plane has moved down relative to the rock below

§  Normal polarity -  A magnetic field that is the same as that which exists at present.

§  Nova -  A star that explosively increas­es in brightness.

§  Nucleus -  The small heavy core of an atom that contains all of its positive charge and most of its mass.

§  Nuee ardente -  Incandescent volcanic debris buoyed up by hot gases that moves downslope in an avalanche fashion.

§  Numerical age dating - establishing the approximate age in years of a particular layer of rock by analyzing the decay of radioactive elements.

§  Numerical date -  Date that specifies the actual number of years that have passed since an event occurred.

§  Objective lens -  In a refracting tele­scope, the long-focal-length lens that forms an image of the object viewed. The lens closest to the object.

§  Obliquity -  The angle between the planes of Earth's equator and orbit.

§  Obsidian -  A volcanic glass of felsic composition.

§  Occluded front -  A front formed when a cold front overtakes a warm front. It marks the beginning of the end of a middle-latitude cyclone.

§  Occlusion -  The overtaking of one front by another.

§  Occultation -  An eclipse of a star or planet by the Moon or a planet.

§  Ocean basinfloor -  Area of the deep-ocean floor between the continental margin and the mid-ocean ridge.

§  Oceanic plateau -  An extensive region on the ocean floor composed of thick accumulations of pillow basalts and other mafic rocks that in some cases exceed 30 kilometers in thickness.

§  Oceanic ridge -  A continuous elevat­ed zone on the floor of all the major ocean basins and varying in width from 500 to 5000 kilometers (300 to 3000 mites). The rifts at the crests of ridges represent divergent plate boundaries.

§  Oceanic zone -  The marine-life zone beyond the continental shelf.

§  Oceanography -  The scientific study of the oceans and oceanic phenomena.

§  Offshore zone -  The relatively flat submerged zone that extends from the breaker line to the edge of the conti­nental shelf.

§  Oort cloud -  A spherical shell com­posed of comets that orbit the Sun at distances generally greater than 10,000 times the Earth-Sun distance.

§  Open cluster -  A loosely formed group of stars of similar origin

§  Open system -  One in which both matter and energy flow into and out of the system. Most natural systems are of this type.

§  Orbit -  The path of a body in revolu­tion around a center of mass.

§  Ore -  Usually a useful metallic miner­al that can be mined at a profit. The term is also applied to certain non­metallic minerals such as fluorite and sulfur.

§  Original horizontality -  Layers of sediments are generally deposited in a horizontal or nearly horizontal position.

§  Orogenesis - The processes that col­lectively result in the formation of mountains.

§  Orographic lifting -  Mountains acting as barriers to the flow of air, forcing the air to ascend. The air cools adiabat­ically and clouds and precipitation may result.

§  Outer core -  A layer beneath the man­tle about 2200 kilometers (1364 miles) thick that has the properties of a liquid.

§  Outer planets See Jovian planets.

§  Outgassing - The escape of gases that had been dissolved in magma.

§  Outwash plain -  A relatively flat, gen­tly sloping plain consisting of materi­als deposited by meltwater streams in front of the margin of an ice sheet.

§  Overrunning - Warm air gliding up a retreating cold air mass.

§  Oxbow lake - A curved lake produced when a stream cuts off a meander.

§  Oxide - an oxide is a chemical compound containing at least one oxygen atom and other elements. Most of the earth's crust consists of oxides. Oxides result when elements are oxidized by oxygen in the air.

§  Ozone - A molecule of oxygen con­taining three oxygen atoms.

§  Pahoehoe - A lava flow with a smooth-to-ropey surface.

§  Paleomagnetism -  The natural rem­nant magnetism in rock bodies. The permanent magnetization acquired by rock that can be used to determine the location of the magnetic poles and the latitude of the rock at the time it be­came magnetized.

§  Paleontology - The systematic study of fossils and the history of life on Earth.

§  Paleozoic era - A span on the geo­logic time scale between the eons of the Precambrian and Mesozoic era from about 540 million to 248 million years ago.

§  Pangaea - The proposed superconti­nent that 200 million years ago began to break apart and form the present landmasses.

§  Parabolic dunes - The shape of these dunes resembles barchans, except their tips point into the wind; they often form along coasts that have strong on‑shore winds, abundant sand, and veg­etation that partly covers the sand.

§  Paradigm - A theory that is held with a very high degree of confidence and is comprehensive in scope.

§  Parallax - The apparent shift of an ob­ject when viewed from two different locations.

§  Parasitic cone - A volcanic cone that forms on the flank of a larger volcano.

§  Parcel - An imaginary volume of air enclosed in a thin elastic cover. Typi­cally it is considered to be a few hun­dred cubic meters in volume and is assumed to act independently of the surrounding air.

§  Parent isotope - An element that undergoes nuclear decay.

§  Parent material - The material upon which a soil develops.

§  Parent rock – when discussing a rock that has undergone change, the parent rock is the rock that existed before change took place, or from where the current rock was transported.

§  Parsec - The distance at which an ob­ject would have a parallax angle of 1 second of arc (3.26 light-years).

§  Partial melting - The process by which most igneous rocks melt. Since individ­ual minerals have different melting points, most igneous rocks melt over a temperature range of a few hundred de­grees. If the liquid is squeezed out after some melting has occurred, a melt with a higher silica content results.

§  Passive continental margin - Margins that consist of a continental shelf, con­tinental slope, and continental rise. They are not associated with plate boundaries and therefore experience little volcanism and few earthquakes.

§  Pegmatite - A very coarse-grained igneous rock (typically granite) com­monly found as a dike associated with a large mass of plutonic rock that has smaller crystals. Crystalliza­tion in a water-rich environment is believed to be responsible for the very large crystals.

§  Pelagic zone - Open ocean of any depth. Animals in this zone swim or float freely.

§  Penumbra - The portion of a shadow from which only part of the light source is blocked by an opaque body.

§  Perched water table - A localized zone of saturation above the main water table created by an impermeable layer (aquiclude).

§  Peridotite - An igneous rock of ultra­mafic composition thought to be abun­dant in the upper mantle.

§  Perihelion - The point in the orbit of a planet where it is closest to the Sun.

§  Period - A basic unit of the geologic calendar that is a subdivision of an era. Periods may be divided into smaller units called epochs.

§  Periodic table - The tabular arrange­ment of the elements according to atomic number.

§  Permeability -  A measure of a materi­al's ability to transmit water

§  Perturbation -  The gravitational dis­turbance of the orbit of one celestial body by another,

§  Phanerozoic eon - That part of geo­logic time represented by rocks con­taining abundant fossil evidence. The eon extending from the end of the Pro­terozoic eon (about 540 million years ago) to the present.

§  Phases of the Moon - The progres­sion of changes in the Moon's appear­ance during the month.

§  Pheoncryst - Conspicuously large crystals embedded in a matrix of finer-grained crystals.

§  Photic zone - The upper part of the ocean into which any sunlight pene­trates.

§  Photochemical reaction - A chemical reaction in the atmosphere that is trig­gered by sunlight, often yielding a sec­ondary pollutant.

§  Photon - A discrete amount (quan­tum) of electromagnetic energy.

§  Photosphere - The region of the Sun that radiates energy to space. The visi­ble surface of the Sum.

§  Photosynthesis - The process by which plants and algae produce carbohy­drates from carbon dioxide and water in the presence of chlorophyll, using light energy and releasing oxygen.

§  pH scale -  A common measure of the degree of acidity or alkalinity of a solu­tion, it is a logarithmic scale ranging from 0 to 14. A value of 7 denotes a neutral solution, values below 7 indi­cate greater acidity, and numbers above 7 indicate greater alkalinity

§  Physical environment -  The part of the environment that encompasses water, air, soil, and rock, as well as conditions such as temperature, humidity, and sunlight.

§  Phytoplankton - Algal plankton, which are the most important commu­nity of primary producers in the ocean.

§  Piedmont glacier - A glacier that forms when one or more valley gla­ciers emerge from the confining walls of mountain valleys and spread out to create a broad sheet in the lowlands at the base of the mountains.

§  Pipe - A vertical conduit through which magmatic materials have passed.

§  Placer - Deposit formed when heavy minerals are mechanically concentrat­ed by currents, most commonly streams and waves. Placers are sources of gold, tin, platinum, diamonds, and other valuable minerals.

§  Plane of the ecliptic - The imaginary plane that connects Earth's orbit with the celestial sphere.

§  Planetary nebula - A shell of incan­descent gas expanding from a star.

§  Plankton - Passively drifting or weakly swimming organisms that cannot move independently of ocean currents. In­cludes microscopic algae, protozoa, jelly­fish, and larval forms of many animals.

§  Plate - One of numerous rigid sections of the lithosphere that moves as a unit over the material of the asthenosphere.

§  Plate tectonics - The theory that pro­poses that Earth's outer shell consists of individual plates that interact in various ways and thereby produce earthquakes, volcanoes, mountains, and the crust itself.

§  Playa - A flat area on the floor of an undrained desert basin. Following heavy rain, the playa becomes a lake.

§  Playa lake - A temporary lake in a playa.

§  Pleistocene epoch - An epoch of the Quaternary period beginning about 1.8 million years ago and ending about 10,000 years ago. Best known as a time of extensive continental glaciations.

§  Plucking (quarrying) -  The process by which pieces of bedrock are lifted out of place by a glacier.

§  Pluton - A structure that results from the emplacement and crystallization of magma beneath the surface of Earth.

§  Pluvial lake -  A lake formed during a period of increased rainfall. During the Pleistocene epoch this occurred in some nonglaciated regions during pe­riods of ice advance elsewhere.

§  Polar (P) air mass -  A cold air mass that forms in a high-latitude source region.

§  Polar easterlies -  In the global pattern of prevailing winds, winds that blow from the polar high toward the subpo­lar low. These winds, however, should not be thought of as persistent winds, such as the trade winds.

§  Polar front - The stormy frontal zone separating air masses of polar origin from air masses of tropical origin.

§  Polar high - Anticyclones that are as­sumed to occupy the inner polar re­gions and are believed to be thermally induced, at least in part.

§  Polar wandering - As the result of pa­leomagnetic studies in the 1950s, re­searchers proposed that either the magnetic poles migrated greatly through time or the continents had gradually shifted their positions.

§  Population I - Stars rich in atoms heavier than helium. Nearly always relatively young stars found in the disk of the galaxy.

§  Population II - Stars poor in atoms heavier than helium. Nearly always relatively old stars found in the halo, globular clusters, or nuclear bulge.

§  Porosity - The volume of open spaces in rock or soil.

§  Porphyritic - An igneous texture con­sisting of large crystals embedded in a matrix of much smaller crystals. Positive feedback mechanism A feedback mechanism that enhances or drives change.

§  Precambrian -  All geologic time prior to the Paleozoic era.

§  Precession -  A slow motion of Earth's axis that traces out a cone over a peri­od of 26,000 years.

§  Precipitation fog - Fog formed when rain evaporates as it falls through a layer of cool air.

§  Pressure – is the force per unit area applied on a surface in a direction perpendicular to that surface.  (from Wikipedia free encyclopedia)

§  Pressure gradient - The amount of pressure change occurring over a given distance.

§  Pressure tendency - The nature of the change in atmospheric pressure over the past several hours. It can be a useful aid in short-range weather prediction.

§  Prevailing wind - A wind that consis­tently blows from one direction more than from another.

§  Primary pollutants - Those pollutants emitted directly from identifiable sources.

§  Primary productivity - The amount of organic matter synthesized by organisms from inorganic substances through photosynthesis or chemosynthesis within a given volume of water or habitat in a unit of time.

§  Primary (P=') wave - A type of seismic wave that involves alternating com­pression and expansion of the material through which it passes.

§  Principal shells See Energy levels. -  

§  Prominence - A concentration of ma­terial above the solar surface that ap­pears as a bright archlike structure.

§  Proterozoic eon - The eon following the Archean and preceding the Phanerozoic. It extends between about 2500 million (2.5 billion) and 540 million years ago

§  Proton-proton chain - A chain of thermonuclear reactions by which nu­clei of hydrogen are built up into nu­clei of helium.

§  Protostar - A collapsing cloud of gas and dust destined to become a star.

§  Psychrometer - A device consisting of two thermometers (wet bulb and dry bulb) that is rapidly whirled and, with the use of tables, yields the relative hu­midity and dew point.

§  Ptolemaic system -  An Earth-centered system of the universe.

§  Pulsar - A variable radio source of small size that emits radio pulses in very regular periods.

§  Pulsating variable - A variable star that pulsates in size and luminosity.

§  Pycnocline - A layer of water in which there is a rapid change of density with depth.

§  Pyroclastic - An igneous rock texture resulting from the consolidation of in­dividual rock fragments that are eject­ed during a violent eruption.

§  Pyroclastic flow - A highly heated mixture, largely of ash and porn ice fragments, traveling down the flanks of a volcano or along the surface of the ground.

§  Pyroclastic material - The volcanic rock ejected during an eruption, in­cluding ash, bombs, and blocks.

§  Radial pattern - A system of streams running in all directions away from a central elevated structure, such as a volcano.

§  Radiation -  The transfer of energy (heat) through space by electromagnet­ic waves

§  Radiation fog - Fog resulting from ra­diation heat loss by Earth.

§  Radiation pressure - The force exert­ed by electromagnetic radiation from an object such as the Sun.

§  Radioactivity - The spontaneous decay of certain unstable atomic nuclei. Radiocarbon (carbon-14) The ra­dioactive isotope of carbon, which is produced continuously in the atmos­phere and is used in dating events from the very recent geologic past (the last few tens of thousands of years).

§  Radio interferometer - Two or more radio telescopes that combine their sig­nals to achieve the resolving power of a larger telescope.

§  Radiornotric dating - The procedure of calculating the absolute ages of rocks and minerals that contain ra­dioactive isotopes.

§  Radio telescope - A telescope de­signed to make observations in radio wavelengths.

§  Raindrop – has a volume equal to roughly 1 million cloud droplets (Earth Science 11e pg 491).

§  Rainshadow desert - A dry area on the lee side of a mountain range. Many middle-latitude deserts are of this type.

§  Rapids - A part of a stream channel in which the water suddenly begins flow­ing more swiftly and turbulently be­cause of an abrupt steepening of the gradient.

§  Ray (lunar) - Any of a system of bright elongated streaks, sometimes associat­ed with a crater on the Moon.

§  Recessional moraine - An end moraine formed as the ice front stag­nated during glacial retreat.

§  Recorded History – started about 5,000 years ago (pg 586 Earth Science 11e).

§  Rectangular pattern - A drainage pat­tern characterized by numerous right-angle bends that develops on jointed or fractured bedrock.

§  Red giant - A large, cool star of high luminosity; a star occupying the upper-right portion of the Hertzsprung-Russell diagram.

§  Reef A strip or ridge of rocks, sand, or coral that rises to or near the surface of a body of water

§  Reflecting telescope -  A telescope that concentrates light from distant ob­jects by using a concave mirror.

§  Reflection - The process whereby light bounces hack from an object at the same angle at which it encounters a surface and with the same intensity.

§  Reflection nebula - A relatively dense dust cloud in interstellar space that is illuminated by starlight.

§  Refracting telescope - A telescope that employs a lens to bend and con­centrate the light from distant objects.

§  Refraction - The process by which the portion of a wave in shallow water slows, causing the wave to bend and tend to align itself with the underwa­ter contours.

§  Regional metamorphism - Metamorphism associated with large-scale mountain-building processes.

§  Regolith - The layer of rock and min­eral fragments that nearly everywhere covers Earth's surface.

§  Relative dating - Rocks are placed in their proper sequence or order. Only the chronological order of events is de­termined.

§  Relative humidity - The ratio of the air's water-vapor content to its water-vapor capacity.

§  Renewable resource - A resource that is virtually inexhaustible or that can be replenished over relatively short time spans.

§  Reserve - Already identified deposits from which minerals can be extracted profitably.

§  Residual soil - Soil developed directly from the weathering of the bedrock below.

§  Resolving power - The ability of a tel­escope to separate objects that would otherwise appear as one.

§  Retrograde motion - The apparent westward motion of the planets with respect to the stars.

§  Reverse fault - A fault in which the material above the fault plane moves up in relation to the material below.

§  Reverse polarity -  A magnetic field op­posite to that which exists at present.

§  Revolution - The motion of one body about another, as Earth about the Sun. Richter scale A scale of earthquake magnitude based on the motion of a seismograph.

§  Richter scale -  

§  Ridge push - A mechanism that may contribute to plate motion. It involves the oceanic lithosphere sliding down the oceanic ridge under the pull of gravity.

§  Rift zone -  A region of Earth's crust along which divergence is taking place.

§  Right ascension - An angular distance measured eastward along the celestial equator from the vernal equinox. Used with declination in a coordinate sys­tem to describe the position of celestial bodies.

§  Rime - A thin coating of ice on objects produced when supercooled fog droplets freeze on contact.

§  Rock -  A consolidated mixture of minerals.

§  Rock cycle - A model that illustrates the origin of the three basic rock types and the interrelatedness of Earth mate­rials and processes.

§  Rock flour - Ground-up rock produced by the grinding effect of a glacier.

§  Rockslide - The rapid slide of a mass of rock downslope along planes of weakness.

§  Rotation - The spinning of a body, such as Earth, about its axis.

§  Runoff - Water that flows over the land rather than infiltrating into the ground.

§  Salinity - The proportion of dissolved salts to pure water, usually expressed in parts per thousand (%o).

§  Saltation  -  Transportation of sediment through a series of leaps or bounces.

§  Santa Ana - The local name given a chinook wind in southern California.

§  Saturation - The maximum quantity of water vapor that the air can hold at any given temperature and pressure.

§  Scattering - The redirecting (in all di­rections) of light by small particles and gas molecules in the atmosphere. The result is diffused light.

§  Scoria - Hardened lava that has retained the vesicles produced by escaping gases. Scoria cone See Cinder cone.

§  Sea – that salt waters that cover the greater part of the earth's surface, or, a division of these waters, of considerable extent, more or less definitely marked off by land boundaries: the North Sea, or, a large lake or landlocked body of water.

§  Sea arch - An arch formed by wave erosion when caves on opposite sides of a headland unite.

§  Sea breeze - A local wind blowing from the sea during the afternoon in coastal areas.

§  Seafloor spreading - The process of producing new seafloor between two diverging plates.

§  Seamount - An isolated volcanic peak that rises at least 1000 meters (3000 feet) above the deep-ocean floor.

§  Sea stack - An isolated mass of rock standing just offshore, produced by wave erosion of a headland.

§  Seawall - A barrier constructed to pre­vent waves from reaching the area be­hind the wall. Its purpose is to defend property from the force of breaking

§  Secondary enrichment - The concen­tration of minor amounts of metals that are scattered through unweathered rock into economically valuable concentra­tions by weathering processes.

§  Secondary pollutants - Pollutants that are produced in the atmosphere by chemical reactions that occur among primary pollutants.

§  Secondary (S) wave -  A seismic wave that involves oscillation perpendicular to the direction of propagation.

§  Sediment - Unconsolidated particles created by the weathering and erosion of rock, by chemical precipitation from solution in water, or from the secre­tions of organisms and transported by water, wind, or glaciers.

§  Sedimentary rock -  Rock formed from the weathered products of preexisting rocks that have been transported, de­posited, and lithified.

§  Seismic sea wave - A rapidly moving ocean wave generated by earthquake activity capable of inflicting heavy damage in coastal regions.

§  Seismogram - The record made by a seismograph.

§  Seismograph - An instrument that records earthquake waves.

§  Seismology - The study of earth­quakes and seismic waves.

§  Semiarid See Steppe.

§  Semidiurnal tidal pattern - A tidal pattern exhibiting two high tides and two low tides per tidal day with small inequalities between successive highs and successive lows; a semi-daily tide.

§  Sensible heat – Is potential energy in the form of thermal energy or heat. The thermal body must have a temperature higher than its surroundings, (also see: latent heat). The thermal energy can be transported via conduction, convection, radiation or by a combination thereof. The quantity or magnitude of sensible heat is the product of the body's mass, its specific heat capacity and its temperature above a reference temperature. In many cases the reference temperature is inferred from common knowledge, i.e. "room temperature".

§  Shadow zone -  The zone between 104 and 143 degrees distance from an earthquake epicenter in which direct waves do not arrive because of refrac­tion by Earth's core.

§  Sheeting -  A mechanical weathering process characterized by the splitting off of slablike sheets of rock.

§  Shelf break -  The point where a rapid steepening of the gradient occurs, marking the outer edge of the conti­nental shelf and the beginning of the continental slope.

§  Shield -  A large, relatively flat expanse of ancient metamorphic rock within the stable continental interior.

§  Shield volcano -  A broad, gently slop­ing volcano built from fluid basaltic lavas.

§  Shore -  Seaward of the coast, this zone extends from the highest level of wave action during storms to the lowest tide level.

§  Shoreline -  The line that marks the contact between land and sea. It mi­grates up and down as the tide rises and falls.

§  Sidereal day -  The period of Earth's rotation with respect to the stars.

§  Sidereal month - A time period based on the revolution of the Moon around Earth with respect to the stars.

§  Silicate -  Any one of numerous miner­als that have the oxygen and silicon tetrahedron as their basic structure.

§  Silicon-oxygen tetrahedron -  A struc­ture composed of four oxygen atoms surrounding a silicon atom that consti­tutes the basic building block of sili­cate minerals.

§  Sill -  A tabular igneous body that was intruded parallel to the layering of pre­existing rock.

§  Sinkhole -  A depression produced in a region where soluble rock has been re­moved by groundwater.

§  Slab pull -  A mechanism that con­tributes to plate motion in which cool, dense oceanic crust sinks into the man­tle and "pulls" the trailing lithosphere along.

§  Sleet -  Frozen or semifrozen rain formed when raindrops freeze as they pass through a layer of cold air.

§  Slide -  A movement common to mass-wasting processes in which the material moving downslope remains fairly coherent and moves along a well-defined surface.

§  Slip face -  The steep, leeward slope of a sand dune; it maintains an angle of about 34 degrees.

§  Slump -  The downward slipping of a mass of rock or unconsolidated material moving as a unit along a curved surface.

§  Snow -  A solid form of precipitation produced by sublimination of water vapor.

§  Snowfield -  An area where snow per­sists year-round.

§  Snowline -  Lower limit of perennial snow.

§  Soil -  A combination of mineral and organic matter, water, and air; that por­tion of the regolith that supports plant growth.

§  Soil horizon A layer of soil that has identifiable characteristics produced by chemical weathering and other soil-forming processes.

§  Soil profile -  A vertical section through a soil showing its succession of horizons and the underlying parent material.

§  Soil Taxonomy -  A soil classification system consisting of six hierarchical categories based on observable soil characteristics. The system recognizes 12 soil orders.

§  Soil texture -  The relative proportions of clay, silt, and sand in a soil. Texture strongly influences the soil's ability to retain and transmit water and air.

§  Solar constant -  The rate at which solar radiation is received outside Earth's atmosphere on a surface per­pendicular to the Sun's rays when Earth is at an average distance from the Sun.

§  Solar eclipse -  An eclipse of the Sun.

§  Solar flare -  A sudden and tremendous eruption in the solar chromosphere.

§  Solar winds -  Subatomic particles eject­ed at high speed from the solar corona.

§  Solifluction -  Slow, downslope flow of water-saturated materials common to permafrost areas.

§  Solstice -  The time when the vertical rays of the Sun are striking either the Tropic of Cancer or the Tropic of Capri­corn. Solstice represents the longest or shortest day (length of daylight) of the year.

§  Solum -  The O, A, and B horizons in a soil profile. Living roots and other plant and animal life are largely con­fined to this zone.

§  Sorting -  The process by which solid particles of various sizes are separated by moving water or wind. Also, the degree of similarity in particle size in sediment or sedimentary rock.

§  Source region -  The area where an air mass acquires its characteristic proper­ties of temperature and moisture. Specific gravity The ratio of a sub­stance's weight to the weight of an equal volume of water.

§  Specific humidity – The mass of water vapor per unit mass of air, including the water vapor (usually expressed as grams of water vapor per kilogram of air).

§  Spectral class -  A classification of a star according to the characteristics of its spectrum.

§  Spectroscope -  An instrument for di­rectly viewing the spectrum of a light source.

§  Spectroscopy -  The study of spectra

§  Spheroidal weathering -  Any weath­ering process that tends to produce a spherical shape from an initially blocky shape.

§  Spicule -  A narrow jet of rising materi­al in the solar chromosphere.

§  Spiral galaxy -  A flattened, rotating galaxy with pinwheel-like arms of in­terstellar material and young stars winding out from its nucleus.

§  Spit -  An elongate ridge of sand that projects from the land into the mouth of an adjacent bay.

§  Spring -  A flow of groundwater that emerges naturally at the ground sur­face.

§  Spring equinox -  The equinox that oc­curs on March 21-22 in the Northern Hemisphere and on September 21-23 in the Southern Hemisphere.

§  Spring tide -  Highest tidal range that occurs near the times of the new and full moons.

§  Stable air -  Air that resists vertical displacement. If it is lifted, adiabatic cooling will cause its temperature to be lower than the surrounding environment; if it is allowed, it will sink to its original position.

§  Stable platform -  That part of the era-ton that is mantled by relatively unde­formed sedimentary rocks and underlain by a basement complex of igneous and metamorphic rocks.

§  Stalactite -  The icicle-like structure that hangs from the ceiling of a cavern.

§  Stalagmite - The columnlike form that grows upward from the floor of a cavern.

§  Star dune -  Isolated hill of sand that exhibits a complex form and develops where wind directions are variable.

§  Stationary front -  A situation in which the surface position of a front does not move; the flow on either side of such a boundary is nearly parallel to the position of the front.

§  Steam fog -  Fog having the appear­ance of steam, produced by evapora­tion from a warm water surface into the cool air above.

§  Stellar parallax -  A measure of stellar distance.

§  Steppe -  One of the two types of dry climate. A marginal and more humid variant of the desert that separates it from bordering humid climates.

§  Stony-iron meteorite -  One of the three main categories of meteorites. This group, as the name implies, is a mixture of iron and silicate minerals.

§  Stony meteorite -  One of the three main categories of meteorites. Such meteorites are composed largely of sili­cate minerals with inclusions of other minerals.

§  Storm surge -  The abnormal rise of the sea along a shore as a result of strong winds.

§  Strata -  Parallel layers of sedimentary rock.

§  Stratified drift -  Sediments deposited by glacial meltwater.

§  Stratopause -  The boundary between the stratosphere and the mesosphere.

§  Stratosphere -  The layer of the atmos­phere immediately above the tropo­sphere, characterized by increasing temperatures with height, owing to the concentration of ozone.

§  Stratovolcano See Composite cone.

§  Stratus -  One of three basic cloud forms; also, the name given one of the flow clouds. They are sheets or layers that cover much or all of the sky. Streak The color of a mineral in powdered form.

§  Stream valley -  The channel, valley floor, and sloping valley walls of a stream.

§  Striations (glacial) -  Scratches or grooves in a bedrock surface caused by the grinding action of a glacier and its load of sediment.

§  Strike-slip fault -  A fault along which the movement is horizontal.

§  Stromatolite -  Structures that are de­posited by algae and consist of layered mounds of calcium carbonate.

§  Subarctic climate -  A climate found north of the humid continental climate and south of the polar climate and characterized by bitterly cold winters and short cool summers. Places within this climatic realm experience the highest annual temperature ranges on Earth.

§  Subduction -  The process of thrusting oceanic lithosphere into the mantle along a convergent boundary

§  Subduction zone -  A long, narrow zone where one lithospheric plate de­scends beneath another.

§  Sublimation -  The conversion of a solid directly to a gas without passing through the liquid state.

§  Submarine canyon -  A seaward exten­sion of a valley that was cut on the continental shelf during a time when sea level was lower, or a canyon carved into the outer continental shelf, slope, and rise by turbidity currents.

§  Submergent coast -  A coast with a form that is largely the result of the partial drowning of a former land sur­face either because of a rise of sea level or subsidence of the crust or both.

§  Subpolar low -  Low pressure located at about the latitudes of the Arctic and Antarctic circles, In the Northern Hemisphere the low takes the form of individual oceanic cells; in the South­ern Hemisphere there is a deep and continuous trough of low pressure.

§  Subsoil -  A term applied to the B hori­zon of a soil profile.

§  Subtropical high -  Not a continuous belt of high pressure but rather several semipermanent, anticyclonic centers characterized by subsidence and diver­gence located roughly between lati­tudes 25 and 35 degrees.

§  Summer solstice -  The solstice that oc­curs on June 21-22 in the Northern Hemisphere and on December 21-22 in the Southern Hemisphere.

§  Sunspot -  A dark spot on the Sun, which is cool by contrast to the sur­rounding photosphere.

§  Supercooled -  The condition of water droplets that remain in the liquid state at temperatures well below 0°C.

§  Supergiant -  A very large star of high luminosity.

§  Supernova -  An exploding star that increases in brightness many thou­sands of times.

§  Superposition -  In any undeformed sequence of sedimentary rocks, each bed is older than the layers above and younger than the layers below.

§  Supersaturation -  The condition of being more highly concentrated than is normally possible under given temper­ature and pressure conditions. When describing humidity, it refers to a rela­tive humidity that is greater than 100 percent.

§  Surf -  A collective term for breakers; also, the wave activity in the area be­tween the shoreline and the outer limit of breakers.

§  Surface area - the area of a rock’s surface exposed to weathering. The more area exposed the faster chemical weathering can proceed.

§  Surface soil -  The uppermost layer in a soil profile: the A horizon.

§  Surface waves -  Seismic waves that travel along the outer layer of Earth.

§  Suspended load -  The fine sediment carried within the body of flowing water.

§  Swells -  Wind-generated waves that have moved into an area of weaker winds or calm.

§  Syncline -  A linear downfold in sedi­mentary strata; the opposite of anticline.

§  Synodic month -  The period of revo­lution of the Moon with respect to the Sun, or its cycle of phases.

§  System -  Any size group of interacting parts that form a complex whole (ES11e, pg 21).

§  Talus - An accumulation of rock debris at the base of a cliff.

§  Tarn -  A small lake in a cirque

§  Tectonics - The study of the large-scale processes that collectively deform Earth's crust.

§  Temperate – free of extremes, mild, (from

§  Temperature -  A measure of the de­gree of hotness or coldness of a sub­stance; a measure of the average kinetic energy of individual atoms or mole­cules in a substance.

§  Temperature inversion -  A layer in the atmosphere of limited depth where the temperature increases rather than decreases with height.

§  Temporary (local) base level -  The level of a lake, resistant rock layer, or any other base level that stands above sea level.

§  Terminal moraine -  The end moraine marking the farthest advance of a glacier.

§  Terrace -  A flat, benchlike structure produced by a stream, which was left elevated as the stream cut downward.

§  Terrae - The extensively cratered high­land areas of the Moon.

§  Terrane -  A crustal block hounded by faults, whose geologic history is dis­tinct from the histories of adjoining crustal blocks.

§  Terrestrial planets -  Any of the Earth-like planets, including Mercury, Venus, Mars, and Earth.

§  Terrigenous sediment -  Seafloorsedi­ments derived from terrestrial weath­ering and erosion.

§  Texture -  The size, shape, and distri­bution of the particles that collectively constitute a rock.

§  Theory -  A well-tested and widely ac­cepted view that explains certain ob­servable facts.

§  Thermal gradient -  The increase in temperature with depth. It averages 1°C per 30 meters (1-2°F per 100 feet) in the crust.

§  Thermal metamorphism See Contact metamorphism.

§  Thermocline -  A layer of water in which there is a rapid change in tem­perature in the vertical dimension.

§  Thermohaline circulation -  Movements of ocean water caused by density differences brought about by variations in temperature and salinity.

§  Thermosphere -  The region of the atmosphere immediately above the mesosphere and characterized by in­creasing temperatures due to absorp­tion of very shortwave solar energy by oxygen.

§  Thrust fault -  A low-angle reverse fault.

§  Thunder -  The sound emitted by rap­idly expanding gases along the chan­nel of lightning discharge.

§  Thunderstorm -  A storm produced by a cumulonimbus cloud and always ac­companied by lightning and thunder. It is of relatively short duration and usually accompanied by strong wind gusts, heavy rain, and sometimes hail.

§  Tidal current -  The alternating hori­zontal movement of water associated with the rise and fall of the tide.

§  Tidal delta -  A deltalike feature creat­ed when a rapidly moving tidal cur­rent emerges from a narrow inlet and slows, depositing its load of sediment.

§  Tidal flat - A marshy or muddy area that is covered and uncovered by the rise and fall of the tide.

§  Tide -  Periodic change in the elevation of the ocean surface.

§  Till -  Unsorted sediment deposited di­rectly by a glacier.

§  Tombolo -  A ridge of sand that con­nects an island to the mainland or to another island.

§  Tornado -  A small, very intense cy­clonic storm with exceedingly high winds, most often produced along cold front, in conjunction with severe thunderstorms.

§  Tornado warning -  A warning issued when a tornado has actually been sighted in an area or is indicated by radar.

§  Tornado watch -  A warning issued for areas of about 65,000 square kilometers (25,000 square miles), indicating that conditions are such that tornadoes may develop; it is intended to alert people to the possibility of tornadoes.

§  Trade winds -  Two belts of winds that blow almost constantly from easterly directions and are located on the equa­torward sides of the subtropical highs.

§  Transform fault  -  A major strike-slip fault that cuts through the lithosphere and accommodates motion between two plates.

§  Transform fault boundary -  A bound­ary in which two plates slide past one another without creating or destroying lithosphere.

§  Transpiration -  The release of water vapor to the atmosphere by plants.

§  Transported soil -  Soils that form on unconsolidated deposits.

§  Transverse dunes -  A series of long ridges oriented at right angles to the prevailing wind; these dunes form where vegetation is sparse and sand is very plentiful.

§  Travertine -  A form of limestone (CaCO3) that is deposited by hot springs or as a cave deposit.

§  Trellis pattern -  A system of streams in which nearly parallel tributaries oc­cupy valleys cut in folded strata.

§  Trench -  An elongated depression in the seafloor produced by bending of oceanic crust during subduction.

§  Trophic level -  A nourishment level in a food chain. Plant and algae producers constitute the lowest level, followed by herbivores and a series of carnivores at progressively higher levels.

§  Tropical depression -  By international agreement, a tropical cyclone with maximum winds that do not exceed 61 kilometers (38 miles) per hour.

§  Tropical rain forest -  A luxuriant broadleaf evergreen forest; also, the name given the climate associated with this vegetation.

§  Tropical storm -  By international agreement, a tropical cyclone with maximum winds between 61 and 119 kilometers (38 and 74 miles) per hour.

§  Tropical wet and dry -  A climate that is transitional between the wet tropics and the subtropical steppes.

§  Tropic of Cancer -  The parallel of lati­tude, 23 1/2 degrees north latitude, marking the northern limit of the Sun's vertical rays.

§  Tropic of Capricorn -  The parallel of latitude, 23 "1 /2 degrees south latitude, marking the southern limit of the Sun's vertical rays.

§  Tropopause -  The boundary between the troposphere and the stratosphere.

§  Troposphere -  The lowermost layer of the atmosphere. It is generally charac­terized by a decrease in temperature with height.

§  Tsunami -  The Japanese word for a seismic sea wave.

§  Tundra climate -  Found almost exclu­sively in the Northern Hemisphere or at high altitudes in many mountainous regions. A treeless climatic realm of sedges, grasses, mosses, and lichens that is dominated by a long, bitterly cold winter.

§  Turbidite -  Turbidity current deposit characterized by graded bedding.

§  Turbidity current -  A downslope movement of dense, sediment-laden water created when sand and mud on the continental shelf and slope are dislodged and thrown into suspension.

§  Turbulent flow -  The movement of water in an erratic fashion often characterized by swirling, whirlpool-like eddies. Most streamflow is of this type.

§  Ultimate base level -  Sea level; the lowest level to which stream erosion could lower the land.

§  Ultramafic -  Igneous rocks composed mainly of iron and magnesium-rich minerals.

§  Ultraviolet -  Radiation with a wave­length from 0.2 to 0.4 micrometer.

§  Umbra -  The central, completely dark part of a shadow produced during an eclipse.

§  Unconformity - A surface that repre­sents a break in the rock record, caused by erosion or nondeposition

§  Uniformitarianism - The concept that the processes that have shaped Earth in the geologic past are essentially the same as those operating today.

§  Unstable air - Air that does not resist vertical displacement. If it is lifted, its temperature will not cool as rapidly as the surrounding environment, so it will continue to rise on its own.

§  Upslope - fog Fog created when air moves up a slope and cools adia­batically.

§  Upwelling - The rising of cold water from deeper layers to replace warmer surface water that has been moved away.

§  Urban heat island - The fact that tem­peratures within a city are generally higher than in surrounding rural areas.

§  Valence electron -  The electrons in­volved in the bonding process; the electrons occupying the highest-princi­pal energy level of an atom.

§  Valley breeze -  The daily upslope winds commonly encountered in a mountain valley.

§  Valley glacier -  See Alpine glacier.

§  Valley train -  A relatively narrow body of stratified drift deposited on a valley floor by meltwater streams that issue from a valley glacier.

§  Vapor pressure -  That part of the total atmospheric pressure attributable to water-vapor content.

§  Vein deposit -  A mineral filling a frac­ture or fault in a host rock. Such de­posits have a sheetlike, or tabular, form.

§  Ventifact -  A cobble or pebble pol­ished and shaped by the sandblasting effect of wind.

§  Vesicular -  A term applied to igneous rocks that contain small cavities called vesicles, which are formed when gases escape from lava.

§  Viscosity -  A measure of a fluid's re­sistance to flow.

§  Visible light -  Radiation with a wave­length from 0.4 to 0.7 micrometer.

§  Volatiles -  Gaseous components of magma dissolved in the melt. Volatiles will readily vaporize (form a gas) at surface pressures.

§  Volcanic bomb -  A streamlined pyro­clastic fragment ejected from a volcano while molten.

§  Volcanic island arc -  A chain of vol­canic islands generally located a few hundred kilometers from a trench where active subduction of one ocean­ic slab beneath another is occurring.

§  Volcanic neck -  An isolated, steep-sided, erosional remnant consisting of lava that once occupied the vent of a volcano.

§  Volcano -  A mountain formed of lava and/or pyroclastics

§  Warm front   -  A front along which a warm air mass overrides a retreating mass of cooler air.

§  Wash -  A common term for a desert stream course that is typically dry ex­cept for brief periods immediately fol­lowing a rain.

§  Water table   -  The upper level of the saturated zone of groundwater.

§  Wave (ocean) - are surface waves that occur in the upper layer of the ocean. They usually result from wind or geologic effects and may travel thousands of miles before striking land. They range in size from small ripples to huge tsunamis. There is little actual forward motion of individual water particles in a wave, despite the large amount of energy and momentum it may carry forward.

§  Wave (not liquid) - a wave is a mode of energy transfer from one place to another, often with little or no permanent displacement of the particles of the medium (i.e. little or no associated mass transport); instead there are oscillations around almost fixed positions. Thus, while mechanical waves require a medium to transverse the distance, electromagnetic waves can travel through a vacuum.

§  Wave-cut cliff -  A seaward-facing cliff along a steep shoreline formed by wave erosion at its base and mass wasting.

§  Wave-cut platform -  A bench or shelf in the bedrock at sea level, cut by wave erosion.

§  Wave depth – for the purposes of CRC geology instructions, this is defined as ½ of the wavelength of an ocean wave. It is the depth beneath water surface at which a wave begins to “feel” the bottom.

§  Wave height   -  The vertical distance between the trough and crest of a wave.

§  Wavelength -  The horizontal distance separating successive crests or troughs.

§  Wave of oscillation -  A water wave in which the wave form advances as the water particles move in circular orbits.

§  Wave of translation -  The turbulent advance of water created by breaking waves.

§  Wave period   -  The time interval be­tween the passage of successive crests at a stationary point.

§  Wave refraction -  See Refraction.

§  Weather - The state of the atmosphere at any given time.

§  Weathering -  The disintegration and decomposition of rock at or near Earth's surface.

§  Welded tuff -  A pyroclastic rock com­posed of particles that have been fused together by the combination of heat still contained in the deposit after it has come to rest and by the weight of overlying material.

§  Well -  An opening bored into the zone of saturation

§  Westerlies -  The dominant west-to­east motion of the atmosphere that characterizes the regions on the pole-ward side of the subtropical highs.

§  Wet adiabatic rate   -  The rate of adia­batic temperature change in saturated air. The rate of temperature change is variable, but it is always less than the dry adiabatic rate.

§  White dwarf -  A star that has ex­hausted most or all of its nuclear fuel and has collapsed to a very small size; believed to be near its final stage of evolution.

§  White frost   -  Ice crystals instead of dew that form on surfaces when the dew point is below freezing.

§  Wind -  Air flowing horizontally with respect to Earth's surface.

§  Wind vane -  An instrument used to determine wind direction.

§  Winter solstice   -  The solstice that oc­curs on December 21-22 in the North­ern Hemisphere and on June 21-22 in the Southern Hemisphere.

§  Yazoo tributary -  A tributary that flows parallel to the main stream be­cause a natural levee is present.

§  Zodiac -  A band along the ecliptic containing the 12 constellations of the zodiac.

§  Zone of accumulation   -  The part of a glacier characterized by snow accumu­lation and ice formation. Its outer limit is the snowline.

§  Zone of aeration   -  Area above the water table where openings in soil, sediment, and rock are not saturated but filled mainly with air.

§  Zone of fracture   -  The upper portion of a glacier consisting of brittle ice.

§  Zone of saturation -  Zone where all open spaces in sediment and rock are completely filled with water.

§  Zone of wastage   -  The part of a gla­cier beyond the zone of accumulation where all of the snow from the previ­ous winter melts, as does some of the glacial ice.

§  Zooplankton -  Animal plankton.