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astronomy study of the universe 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 apogee the point where the moon is farthest from the Earth apparent magnitude the brightness of a star when viewed from Earth aquifer rock or soil throuugh which groundwater moves easily astronomical unit (AU) average distance from Earth to the sun atmosphere the gaseous portion of a planet; the planet's envelope of air; aqueduct a pipe or channel through which water flows from a higher elevation to a lower elevation aurora a bright display of ever changing light caused by solar radiation interacting with the upper atmosphere in the region of the poles barometer instrument that measures atmospheric pressure big bang theory the theory that proposes that the universe originated as a single mass, which subsequently exploded binary star one of two stars revolving around a common center of mass under their mutual gravitational attraction biosphere all life on Earth; the parts of the solid Earth, hydrosphere and atmosphere that living organisms can be found black hole massive star that has collapsed to such a small volume that its gravity prevents the escape of everything, including light caldera a large depression typically caused by collapse or ejection of the summit area of a volcano cementation solidification of sediments by the deposition of dissolved minerals in the tiny spaces between the sedimentary particles chromosphere the first layer of the solar atmosphere found directly aove the photosphere cinder cone a small volcano built primarily of pyroclastic material ejected from a singl vent cleavage tendency of a mineral to break along planes of weak bonding cold front a front along which a cold air mass thrusts beneath a warmer air mass comet a small body made of rocky and metallic pieces held together by frozen gases compaction process by which sediments are squeezed together by the weight of overlying materials driven out by water condensation the change of state from a gas to a liquid conduction the transfer of heat through matter by molecular activity; Energy is transferred through collisions from one molecule to another conservation the careful use of resources constellation an apparent group of stars originally named for mythical characters contact metamorphism changes in rock caused by the heat from a nearby magma body continental drift a hypothesis that originally proposed that the continents had once been joined to form a single supercontinent; the supercontinent broke into several pieces, which drifted to their present day positions 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 convergent boundary a boundary in which two plates move together core the innermost layer of Earth, located beneath the mantle Coriolis Effect the apparet 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 weak layer of the solar atmosphere crater the depression at the summit of a volcano or that which is produced by a meteorite impact cross-cutting relationships, principle of principle of relative dating; a rock or fault is younger than any rock or fault through which it cuts crust the thin, outer layer of Earth crystal form the external appearance of a mineral as determined by its internal arrangement of atoms cyclone a low-pressure center characterized by a counter-clockwise flow of air in the Northern Hemisphere deformation general term for the processes of folding, faulting, shearing, compression, or extension of rocks as the result of various natural forces density mass per unit volume of a substance, usually expressed as grams per cubic centimeter deposition the process by which an agent of erosion loses energy and drops the sediment it is carrying; divergent boundary a region where the rigid plates are moving apart, typified by the oceanic ridges Doppler effect the apparent change in frequency of electromagnetic or sound waves caused by the relative motions of the source and the observer earthquake the vibration of Earth produced by the rapid release of energy Doppler effect the apparent change in frequency of electromagnetic or sound waves caused by the relative motions of the source and the observer elastic rebound hypothesis the explanation stating that when rocks are deformed, they break, releasing the stored energy that results in the vibrations of an earthquake contour lines lines on a topographic map that indicates an elevation contour interval on a topographic map, tells the distance in elevation between adjacent contour lines Earth Science the name for all the sciences that collectively seek to understand Earth; it includes geology, oceanography, meteorology, electromagnetic spectrum the arrangement of electromagnetic radiation according to wavelength ellipse an oval El Nino the name given to the periodic warming of the ocean that occurs in the central and eastern Pacific emission spectrum a series of bright lines of particular wavelengths produced by a hot gas under low pressure epicenter the location on Earth's surface directly above the focus, or origin, of an earthquake erosion the incorporation and transportation of material by a mobile agent, such as water, wind, or ice evaporation the process of converting a liquid to a gas extrusive igneous rock igneous rock that has formed on Earth's surface fault a fracture in Earth along which movement has occurred fault-block mountain a mountain formed when large blocks of crust are tilted, uplifted or dropped between large normal faults flood occurs when the discharge of a stream becomes so great that it exceeds the carrying capacity of its channel and overflows its banks focus the point within Earth where an earthquake originates folded mountain a mountain created primarily by compressional stresses, which create folds in the rock layers foliated metamorphic rock a metamorphic rock with a texture that gives the rock a layered appearance foreshock a small earthquake that often proceeds a major earthquake fossil the remains or traces of an organism preserved from the geologic past fossil fuel general term for any hydrocarbon that may be used as a fuel, including coal, oil, and natural gas fracture any break or rupture in rock along which no appreciable movement has taken place front the boundary between two adjoining air masses having contrasting characteristics frost wedging the mechanical breakup of rock caused by the expansion of freezing water in cracks and crevices galaxy a group of stars, dust, and gases held together by gravity galaxy cluster a system of galaxies containing from several to thousands of member galaxies geocentric describes the concept of an Earth-centered universe geology the science that examines the Earth, its form and composition, and the changes it has undergone and is undergoing geosphere layer of Earth under both the atmosphere and the oceans; composed of the core, mantle and crust geothermal energy energy that can be extracted from Earth's internal heat, for example, natural steam used for power generation geothermal field an area of land where magma lies relatively close to the surface and heats the groundwater geothermal gradient the gradual increase in temperature with depth in the crust global warming the increase in average temperatures of Earth and the atmosphere due in part to increase carbon dioxide levels gradient the slope of a stream over a certain distance granitic composition a compositional group of igneous rocks that indicate a rock is composed almost entirely of light-colored silicates, mainly quartz and feldspar greenhouse effect the heating of Earth's surface and atmosphere from solar radiation being absorbed and emitted by the atmosphere, mainly by water vapor and carbon dioxide groundwater water underground in the zone of saturation hardness the resistance a mineral offers to scratching heliocentric describes the view that the sun is at the center of the solar system heat thermal energy transferred from one object to another hot spot a concentration of heat in the mantle capable of producing magma, which rises to Earth's surface; The Pacific Plate moves over a hot spot, producing the Hawaiian Islands H-R Diagram a plot of stars according to their absolute magnitudes and temperatures Hubble's Law a law that states that the galaxies are retreating from the Milky Way at a speed that is proportional to their distance 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 hurricane a tropical cyclonic storm having winds in excess of 119km per hour hydrogenous sediment seafloor sediment consisting of minerals that crystallize from seawater hydrosphere the water portion of Earth; 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 rock hypothesis a tentative explanation that is tested to determine if it is valid igneous rock a rock formed by the crystallization of molten magma infiltration the movement of surface water into rock or soil through cracks or pore spaces inner core the solid innermost layer of Earth 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 igneous rock igneous rock formed below Earth's surface jet stream swift, high altitude winds Jovian planet the Jupiter like planets; Jupiter, Saturn, Uranus, and Neptune. These planets have relatively low densities and are huge gas giants Koppen Classification System a system for classifying climates based on mean monthly and annual values of temperature and precipitation laccolith a massive igneous body intruded between preexisting strata latitude the distance north or south of the equator, measured in degrees lava magma that reaches Earth's surface light-year the distance light travels in a year, about 9.5 trillion km liquefaction a phenomenon, sometimes associated with earthquakes, in which soils and other unconsolidated materials saturated with water are turned into a liquid that is not able to support buildings lithosphere the rigid outer layer of earth, including the crust and upper mantle longitude the distance east or west of the prime meridian, measured in degrees lunar eclipse an eclipse of the moon; occurs when the moon passes through Earth's shadow lunar regolith a thin. gray layer on the surface of the moon, consisting of loosely compacted, fragmented material believed to have formed by repeated impacts of meteorites luster the appearance or quality of light reflected from the surface of a mineral magma a body of molten rock found at depth, including any dissolved gases and crystals main-sequence star a star that falls into the main sequence category on the H-R diagram; this category contains the majority of stars and runs diagonally from the upper left to the lower right on the H-R diagram mantle layer of Earth located below the crust mass movement the downslope movement of rock, regolith and soil under the direct influence of gravity mechanical weathering the physical disintegration of rock, resulting in smaller fragments mesosphere the layer of the atmosphere immediately above the stratosphere and characterized by decreasing temperatures with height metamorphic rock rock formed by the alteration of pre-existing rock deep within the 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 reaches Earth's surface mineral a naturally occurring, inorganic crystalline material with a unique chemical composition 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, which is derived from the amount of displacement that occurs along a fault zone and estimates the energy released by an earthquake monsoon seasonal reversal of wind direction associated with large continents, especially Asia; mudflow quickly moving downhill flow of soil and rock fragments containing a large amount of water natural hazard an event that results from Earth processes that can cause damage and endanger human life nebula a cloud of gas and/or dust in space neutron star a star of extremely high density composed entirely of neutrons nonfoliated metamorphic rock metamorphic rock that does not exhibit a banded or layered appearance nonrenewable resource resource that takes millions of years to form 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 nuclear fusion the way in which the sun produces energy; ocean current mass of ocean water that flows from one place to another oceanic ridge a continuous elevated zone on the floor of all the major ocean basins and varying in width from 1000-4000km; the rifts at the crests represent divergent plate boundaries oceanography the scientific study of the oceans and oceanic phenomena ore a material from which a useful mineral or minerals can be mined for profit original horizontality, principle of a principle of relative dating; Layers of sediments are generally deposited in a horizontal or nearly horizontal position. orogenesis the processes that collectively result in the formation of mountains ozone a molecule of oxygen containing three oxygen atoms P wave earthquake wave that pushes and pulls rocks in the direction of the wave; also known as a compression wave paleomagnetism the study of changes in Earth's magnetic field, as shown by patterns of magnetism in rocks that have formed over time Pangaea the proposed supercontinent that 200 million years ago began to break apart and form the present landmasses perigee the point at which the moon is closest to the Earth perihelion the point in the orbit of a planet where it is closest to the sun phases of the moon the progression of changes in the moon's appearance during the month photon a small packet of light energy photosphere the region of the sun that radiates energy into space; visible surface of the sun photosynthesis the process by which plants, algae, and certain prokaryotes use light energy to convert water and carbon dioxide into energy rich glucose molecules planetesimal small, irregularly shaped body formed by colliding matter plate one of numerous rigid section 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. pluton an intrusive igneous structure that results from the cooling and hardening of magma beneath the surface of Earth polar easterlies in the global pattern of prevailing winds, winds that blow from the polar high toward the polar low; polar front a stormy frontal zone separating cold air masses of polar origin from warm air masses of tropical origin polar zone the region between 66.5 degrees north and south latitudes and the poles; the sun's rays strike at a very small angle in the polar zone porosity the volume of open spaces in rock or soil precession a slow motion of Earth's axis that traces out a cone over a period of 26,000 years precipitation any form of water that falls from a cloud pressure gradient the amount of pressure change occurring over a given distance prevailing wind a wind that consistently blows from one direction more than from another prominence a concentration of gases above the solar surface that appears as a bright archlike structure protostar a collapsing cloud of dust and gas destined to become a star; a developing star not yet hot enough to engage in nuclear fusion pulsar a variable radio source of small size that emits radio pulses in very regular periods pyroclastic material the volcanic rock ejected during an eruption, including, ash, bombs, and blocks radiation the transfer of energy (heat) through space by electromagnetic waves radioactivity the spontaneous decay of certain unstable atomic nuclei radio telescope a telescope designed to make observations in radio wavelengths ray any of a system of bright elongated streaks, sometimes associated with a crater on the moon red giant a large, cool star of high luminosity; a star occupying the upper right portion of the H-R diagram reflecting telescope a telescope that concentrates light from distant objects by using a concave mirror reflection the process whereby light bounces back from an object at the same angle at which it encounters a surface and with the same intensity refracting telescope a telescope that uses a lens to bend and concentrate the light from distant objects 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 process by which rocks are placed in their proper sequence or order; Only the chronological order of events is determined, not the absolute age in years renewable resource a resource that is virtually inexhaustible or that can be replenished over relatively short time spans reservoir rocks porous rocks in which oil collects and becomes trapped 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 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 valley deep faulted structure found along the axes of divergent plate boundaries; can develop on seafloor or on land rille long channel associated with lunar maria 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 rotation the spinning of a body, such as Earth, about its axis runoff water the flows over the land surface rather than seeping into the ground S wave a seismic wave that shakes particles perpendicular to the direction the wave is traveling salinity the proportion of dissolved salts to pure water, usually expressed in parts per thousand scattering the redirecting (in all directions) of light by small particles and gas molecules in the atmosphere; the result is more light rays with weaker intensity seafloor spreading the process by which plate tectonics produces new oceanic lithosphere at ocean ridges sediment loose 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, compacted and cemented seismic gap an area along a fault where there has not been any earthquake activity for a long period of time seismic shaking a measure of how much ground movement occurs during and earthquake seismogram the record made by a seismograph seismograph an instrument that records earthquake waves 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 lava silicate any one of numerous minerals that have the oxygen and silicon tetrahedron as their basic structure 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 soil a combination of mineral and organic matter, water, and air; that portion of the regolith that supports plant life solar eclipse an eclipse of the sun; a solar eclipse occurs when the moon moves in a line directly between Earth and the sun, casting a shadow on earth solar flare a sudden and tremendous eruption in the solar chromosphere solar wind streams of protons and electrons ejected at high speed from the solar corona source rocks rocks in which oil forms spectroscopy the study of the properties of light that depend on wavelength stratosphere the layer of the atmosphere immediately above the troposphere, characterized by increasing temperatures with height, due to the concentration of ozone streak the color of a mineral in powdered form stress the force per unit area acting on a solid strike-slip fault a fault along which the movement is horizontal and parallel to the trend of the fault stalacite an icicle-like structure that hangs from the ceiling of a cavern stalagmite a columnlike form that grows upward from the floor of the cavern subarctic climate climate found north of the humid continental climate and south of the polar climate; characterized by bitterly cold winters and short cool summers subduction zone a destructive plate margin where oceanic crust is being pushed down into the mantle beneath a second plate sublimation the conversion of a solid directly to a gas without passing through the liquid state sunspot a dark spot on the sun, which is cool by contrast to the surrounding photosphere supergiant a very large, very bright red giant star supernova an exploding star that increases in brightness many 1000s of times superposition, law of a law that states that in any undeformed sequence of sedimentary rocks, each bed is older than the layers above and younger than the layers below surface current movement of water that flows horizontally in the upper part of the ocean's surface surface wave a seismic wave that travels along the surface of the Earth system any size group of interacting parts that form a complex whole temperate zone region located between 23.5 degrees and 66.5 degrees north and south of the equator temperature a measure of the average kinetic energy of individual atoms or molecules in a substance temperature inversion a layer of limited depth in the atmosphere of limited depth where the temperature increases rather than decreases with height terrane a crustal block bounded by faults, whose geologic history is distinct from the histories of adjoining crustal blocks