WGU Geology 1: Physical

Weathering

a mechanical or chemical process that disintegrates bedrock.

Sandy texture

a medium- to coarse-grained aggregate of fused sand grains that esembles sandstone. Unlike sandstone, the grains of these textured metamorphic rocks cannot be rubbed free

Neomorphism

a metamorphic process that changes the mineralogy of the protolith. During this, minerals not only recrystallize but also form new minerals from the existing elements within the protolith.

Regional metamorphism

also known as Barrovian metamorphism, occurs over large areas and is associated with tectonic plate collision, folding rock layers, and mountain building processes. Zones of this are characterized by high pressures, high temperatures, and by intrusions that cool over long periods of time.

Micas

are common metamorphic minerals that form when many different parent rocks undergo metamorphism.are shaped like pie plates. When metamorphism occurs without deformation—without causing the rocks to change shape—they grow with random orientations, like pie plates flying through the air. However, when tectonic force squeezes rocks as they are heated during metamorphism, the rock deforms into folds.

conchoidal fracture

creates smooth, curved surfaces. Some minerals break into splintery or fibrous fragments. Most fracture into irregular shapes.

texture

describes the sizes, shapes, and arrangements of its parts.

chemical weathering

dissolves rock in water and forms biochemical and chemical sedimentary rocks. The decomposition of rock when it chemically reacts with air, water, or other agents in the environment, altering its chemical composition and mineral content.

Foliated metamorphic rocks

exhibit layers or the alignment of minerals, also called foliation. Foliation results from the high stresses and recrystallization processes associated with regional metamorphism.

volcanic

finely crystalline

Chemical sedimentary rock

forms by direct precipitation of minerals from solution. Rock salt, for example, forms when halite precipitates from evaporating seawater or saline lake water.

Coal

forms from the accumulation of peat in swamps and similar environments where dead plants accumulate faster than they can be broken down by decay.

Gradualism

geologic change occurs over long periods of time, by a sequence of almost-imperceptible events.

Uniformitarianism

geologic processes operating today also operated in the past. 'The present is the key to the past.'

striations

hairline grooves, on the cleavage surfaces or crystal faces can also be used to identify minerals. Can be beneficial in distinguishing minerals of the same group, such as plagioclase feldspar.

Replacement chert

has a microcrystalline texture and is formed when minerals are replaced by cryptocrystalline quartz from the precipitation of silica. Petrified wood is an example of this, and is formed when volcanic ash buries a forest creating silica-rich sediment that dissolves in groundwater and precipitates cryptocrystalline quartz within the wood, replacing the wood's cellulose.

Crystalline texture

is a medium- or coarse-grained aggregate of inter-grown visible crystals.

Andesite

is a volcanic rock intermediate in composition between basalt and granite. It is commonly gray or green and consists of plagioclase feldspar and dark minerals (usually biotite, amphibole, or pyroxene). is typically very fine grained.

Peridotite

is an ultramafic (rich in magnesium and iron) igneous rock that makes up most of the upper mantle but is rare in Earth's crust. It is coarse grained and composed of olivine and small amounts of pyroxene, amphibole, or mica, but no feldspar

Bioclastic sedimentary rock

is composed of broken shell fragments and similar remains of living organisms. The fragments are clastic, but they have a biological origin. Many limestones are formed from broken shells and thus are this

nodular chert

is found as irregularly shaped lumps called "nodules" within other sedimentary rocks

Komatiite

is the finely crystalline, extrusive equivalent of peridotite. Geologists think that it was the material of the earliest crust that formed as the molten planet cooled more than 4 billion years ago. Only a few traces of this primordial crust are known to exist today.

Diorite

is the plutonic equivalent of andesite. It forms from the same magma as andesite and, consequently, often underlies andesitic mountain chains such as the Andes.

Evaporites

rocks that form when evaporation concentrates the salts to the point at which they precipitate from solution

Evaporites

salt deposits formed from the evaporation of saltwater. The type of rock formed is dependent on the amount of evaporation. For example, gypsum is formed when 50-75% of the saltwater has evaporated, whereas halite is formed when 90% of the saltwater has evaporated.

Composition

what the sediments are made of, whether it is rock fragments, mineral grains, or organic materials. An acid test using dilute HCl can also be used to determine the composition of sedimentary rocks.

playa lake

A temporary desert lake that dries up during the dry season.

Benioff zone

A three-dimensional zone of earthquake foci within and along the upper portion of a subducting plate; formed by release of strain as the subducting plate scrapes past the overriding plate.

Glaciation

A time when alpine glaciers descend into lowland valleys and continental glaciers grow over high-latitude continents;

drainage divide

A topographic high separating drainage basins.

thrust fault

A type of reverse fault that is nearly horizontal, with a dip of 45 degrees or less over most of its extent.

Slump

A type of slide in which blocks of material slide downslope as a consolidated unit over an upward-convave, curved fracture in rock or regolith; trees on these blocks tilt uphill. The uphill portion of this usually consists of several tilted slide blocks, whereas the toe of this usually consists of rumpled, folded sediment.

strike-slip fault

A vertical fault across which rocks on opposite sides move horizontally.

Chalk

A very fine-grained limestone made up of the remains of tiny marine microorganisms.

Histosols

A very organic-rich soil, typically formed in a poorly drained area where stagnant water inhibits organic decay. Typically composed of thick O and A horizons. Can be mined as peat.

Stratified drift

Glacial drift that was first carried by a glacier and then transported and deposited in layers by a stream.

parabolic dune

A crescent-shaped dune with tips pointing into the wind; forms in moist semidesert regions and along seacoasts where sparse vegetation is present to anchor the tips of the dune.

barchan dune

A crescent-shaped dune, highest in the center, with the tips pointing downwind; typically forms in rocky deserts where there is a general shortage of sand.

oxbow lake

A crescent-shaped lake created where a meander loop is cut off from a stream and the ends of the meander become plugged with sediment.

oligotrophic lake

A deep lake characterized by nearly pure water but with low concentrations of nutrients, thus sustaining relatively few living organisms.

Fjords

A deep, narrow, glacially carved valley on a high-latitude seacoast that was later flooded by encroaching seas as the glaciers melted.

point bar

A deposit of sediment in the slower water on the inside of a meander.

Sinkhole

A depression on Earth's surface caused by the collapse of a cavern roof or by the dissolution of surface rocks, usually limestone.

rain-shadow desert

A desert formed on the downwind side of a mountain range.

stagnant ice

Glacial ice that has broken away from the front of a terrestrial glacier and is no longer connected to the glacier's ice-delivery system.

Cinders

Glassy, pyroclastic volcanic fragments 4 to 32 millimeters in size.

Well

A hole dug or drilled into Earth, generally for the production of water, petroleum, natural gas, brine, or sulfur, or for exploration.

Loess

A homogenous, porous deposit of windblown glacial silt, typically unlayered, that forms vertical bluffs and cliffs. Fertile, agriculturally productive soils—usually mollisols—commonly form on this.

transverse dunes

A relatively long, straight dune with a gently sloping windward side and a steep lee face that is perpendicular to the prevailing wind; forms where sand is plentiful and evenly dispersed.

eutrophic lake

A relatively shallow lake characterized by abundant nutrients, thus sustaining multiple living organisms.

interglacial periods

A relatively warm, ice-free time separating glaciations.

end moraine

A ridge of till that forms at the end, or terminus, of a glacier that is neither advancing nor retreating and whose terminus has remained in the same place for years.

lateral moraine

A ridgelike moraine that forms from sediment on or adjacent to the sides of a mountain glacier.

metamorphic rock

A rock formed when igneous, sedimentary, or other metamorphic rocks recrystallize in response to elevated temperature, increased pressure, chemical change, and/or deformation.

intrusive igneous rock

A rock formed when magma solidifies within Earth's crust without erupting to the surface; usually medium to coarsely crystalline. Also called plutonic rock.

Mercalli scale

A scale of earthquake intensity that expresses the strength of an earthquake based on its destructive power and its effects on buildings and people; does not accurately measure the energy released by the quake

Richter scale

A scale of earthquake magnitude that expresses the amount of energy released; calculated from the amplitude of the largest body wave on a standardized seismograph, although not a precise measure of earthquake energy.

Icefall

A section of a glacier consisting of numerous crevasses and towering ice pinnacles

forearc basin

A sedimentary basin between the oceanic trench and the magmatic arc, either in an island arc or at an Andean margin.

foreland basin

A sedimentary basin formed by downward flexing of continental crust by the weight of thrust plates in a compressional orogen.

Cross-bedding

A sedimentary structure in which wind or water deposits sets of beds that are inclined to the main sedimentary layering.

Spring

A seep or flow of groundwater onto the surface; commonly occurs where the water table intersects the land surface.

paternoster lakes

A series of lakes in a glacial valley, strung out like beads and connected by short streams and waterfalls.

Meanders

A series of twisting curves or loops in the course of a stream.

Arête

A sharp narrow ridge of rock between adjacent valleys or between two cirques, created when two alpine glaciers moved along opposite sides of the mountain ridge and eroded both sides.

Horn

A sharp, pyramid-shaped rock summit where three or more cirques intersect near the summit.

Dike

A sheetlike igneous rock, cutting through layers of country rock, that forms when magma is injected into a fracture.

Sill

A sheetlike igneous rock, parallel to the grain or layering of country rock, that forms when magma is injected between layers.

Kettles

A small depression formed by a block of stagnant ice; many fill with water to become a kettle lake.

hanging valley

A small glacial valley lying high above the floor of the main valley.

Chondrules

A small grain about 1 millimeter in diameter embedded in a meteorite, often containing amino acids or other organic molecules.

Meteoroid

A small interplanetary body, most often an asteroid or comet fragment, traveling in an irregular orbit through the inner Solar System.

Tarn

A small lake at the base of a cirque.

Kame

A small mound or ridge of stratified drift deposited by a stream that flows on top of, within, or beneath a glacier.

cinder cone

A small volcano, typically less than 300 meters high, made up of loose pyroclastic fragments blasted out of a central vent; usually active for only a short time.

transported soils

A soil formed by the weathering of regolith that is transported from somewhere else and deposited.

residual soils

A soil formed from the weathering of bedrock below.

Oxisols

A soil formed in a hot, humid climate and characterized by intensive leaching of soluble cations from the A horizon, little ability to retain nutrients, and very poor fertility. Very insoluble iron and aluminum oxides are concentrated.

Aridisols

A soil formed in arid or semiarid environments and characterized by very low organic content, water deficiency, and precipitation of salts in the B horizon.

Alfisol

A soil formed in semiarid to humid climates, typically under hardwood cover. Characterized by accumulation of clay in the B horizon and relatively high fertility, making it productive for agriculture.

composite cone

A steep-sided volcano formed by an alternating series of lava flows and pyroclastic deposits and marked by repeated eruption.

Stratovolcano

A steep-sided volcano formed by an alternating series of lava flows and pyroclastic eruptions and marked by repeated eruption.

Cirque

A steep-walled, spoon-shaped depression eroded into a mountain peak by a glacier.

solar wind

A stream of electrons and positive ions radiating outward from the Sun at high speed.

intermittent streams

A stream that does not maintain some flow all the time and may be dry for long periods.

outwash stream

A stream that emerges from below the snout of a glacier and carries glacial sediment further downslope.

Tributaries

A stream that feeds water into another stream or river.

braided stream

A stream that flows in many shallow, interconnecting channels that are usually separated by emergent sediment bars; formed because the stream's capacity has been exceeded by its sediment supply.

perennial streams

A stream that maintains some flow even during dry seasons.

graded stream

A stream with a smooth, concave-upward profile, in equilibrium with its sediment supply; it transports all the sediment supplied to it, with neither erosion nor deposition in the streambed.

wash

A streambed that is dry for most of the year

Rockslide

A subcategory of slide mass wasting in which a segment of bedrock slides downslope along a fracture and the rock breaks into fragments and tumbles down the hillside; also called a rock avalanche.

zone of saturation

A subsurface zone below the water table in which all porosity within soil and bedrock is filled with water.

zone of aeration

A subsurface zone located between the ground surface and the water table and in which the pores are mostly filled with air; also called the unsaturated zone

Mollisol

Grassland soil characterized by rich A horizon, high cation exchange capacity, and B horizon rich in base cation salts; very fertile soil.

Compaction

Increased packing together of sedimentary grains, usually resulting from the weight of overlying sediment; causes a decrease in porosity and contributes to lithification.

Tail

The long trailing portion of a comet, always pointing away from the Sun, formed when solar winds blow away lighter particles from the comet's head. What appears to be a fiery arrow is actually reflected light from the Sun.

capillary action

The process by which water is pulled upward through the soil due to the natural attraction of water molecules to soil particles and the cohesion of water.

Subduction

The process in which two lithospheric plates of different densities converge and the denser one sinks into the mantle beneath the other.

orogeny

The process of mountain building; all tectonic processes associated with mountain building.

percentage base saturation

The proportion of a soil's cation exchange capacity that is saturated by basic cations

Porosity

The proportional volume of pores or open space within a material; indicates the maximum possible volume of fluid that could be held within the material.

Luster

The quality and intensity of light reflected from the surface of a mineral.

drainage basin

The region that is drained by a single stream.

Eluviation

The removal and downward movement of dissolved ions and clays from the O, A, and E horizons by infiltrating water.

Erosion

The removal of weathered rocks that occurs when water, wind, ice, or gravity transports the material to a new location.

Hardness

The resistance of a mineral to scratching, controlled by the bond strength between its atoms.

Banks

The rising slopes bordering the sides of a stream channel.

Venus

The second planet from the Sun; resembles Earth in size and density.

Europa

The second-closest of Jupiter's moons; similar to Earth in that much of its interior is composed of rock and much of its surface is covered with water, although the water is frozen into a vast planetary ice crust.

Saturn

The second-largest planet and sixth from the Sun; marked by its distinctive rings.

rock cycle

The sequence of events in which rocks are formed, destroyed, altered, and reformed by geological processes.

Uranus

The seventh planet from the Sun; similar to Neptune in size, composition, and atmosphere.

Limbs

The sides of a fold in rock.

texture

The size, shape, and arrangement of mineral grains, or crystals, in a rock.

volcanic ash

The smallest pyroclastic particles, less than 2 millimeters in diameter.

B horizon

The soil layer just below the A horizon, containing less organic matter and where ions and clays leached from the A and E horizon accumulate; also called subsoil.

Bedrock

The solid rock that lies beneath soil or unconsolidated sediments; it can be igneous, metamorphic, or sedimentary.

escape velocity

The speed that an object must attain to escape the gravitational field of a planet or other object in space.

slip face

The steep leeward side of a dune, typically at the angle of repose for loose sand, so that the sand flows or slips down the face, where it is deposited.

Gradient

The steepness or vertical drop of a stream over a specific distance.

Volcano

A hill or mountain formed from lava and rock fragments ejected from a volcanic vent.

Flood

A relatively high stream discharge that overtops the stream banks, covering land that is not usually underwater.

Isostasy

The concept that the lithosphere floats on the asthenosphere as an iceberg floats on water.

Foliation

The layering in metamorphic rocks resulting from regional dynamothermal metamorphism.

Avulsion

The process by which a stream channel is abandoned and the water and sediment diverted down a new channel

Lithification

The process by which loose sediment is converted to solid rock.

underthrusting

The process by which one continent subducts beneath the other during a continent-continent collision.

desert pavement

A continuous cover of closely packed gravel- or cobble-sized clasts left behind when wind erodes smaller particles such as silt and sand.

Hydrothermal metamorphism

(also called hydrothermal alteration or metasomatism) occurs when hot water and ions dissolved in the hot water react with a rock to change its chemical composition and minerals.

Calcrete

A hardpan that forms in the B soil horizon in arid and semiarid regions when calcium carbonate precipitates and cements the soil particles together.

Gelisol

A high-latitude soil formed over permafrost that is no deeper than two meters. Characterized by an organic-rich A horizon that usually extends to the permafrost boundary.

Charles Darwin

1800's. Natural Selection- nature selects the best adapted varieties to survive to reproduce. The 'fittest' will vary depending on circumstance and environment. Fittest is the most likely to live on to reproduce.

Harry Hess

1962. By studying ocean floor - Ocean floor is at most only a few hundred million years old compared to the 4 billion year old planet. Seafloor spreading led to new molten rock to ooze up in the cracks creating new surface. This supported Wegener's Continental Drift theory. Explained ocean ridges and volcanic islands.

Pluton

A body of intrusive igneous rock. in most cases granitic magma solidifies within Earth's continental crust to form a large mass of igneous rock

intrusion

A body of magma that cools and solidifies below Earth's surface

Aquifer

A body of rock that can yield economically significant quantities of groundwater; should be both porous and permeable.

Aquitards

A body of sediment or rock that has low porosity and permeability and that inhibits the flow of groundwater.

dwarf planets

A body that orbits the Sun, is not a satellite of a planet, and is massive enough to pull itself into a spherical shape, but is not massive enough to clear out other bodies in and near its orbit.

660-kilometer discontinuity

A boundary in the mantle, at a depth of about 660 kilometers, where seismic wave velocities increase because pressure is great enough that the minerals in the mantle recrystallize to form denser minerals.

Crater

A bowl-like depression at the summit of a volcano, created by volcanic activity.

Basin

A bowl-shaped synclinal structure, commonly filled with sediment.

Scarp

A break in the land surface caused by an earthquake.

gibbous moon

A bright moon, either waxing or waning, with only a sliver of dark visible.

lava plateau

A broad plateau covering thousands of square kilometers, formed by the accumulation of many individual lava flows that occur over a short period of geologic time.

Bajada

A broad, gently sloping depositional surface formed by the merging of alluvial fans from closely spaced canyons and extending outward into a desert valley.

Pediment

A broad, gently sloping erosional surface that forms along the front of desert mountains uphill from a bajada, usually covered by a patchy veneer of gravel only a few meters thick.

outwash plain

A broad, gently sloping surface formed when outwash spreads onto a wide valley or plain beyond a glacier.

Column

A cave deposit formed when a stalactite and a stalagmite meet and grow together.

magnetic reversal

A change in Earth's magnetic field in which the north magnetic pole becomes the south magnetic pole and vice versa; has occurred on average every years over the past million years.

Precipitation

A chemical reaction that produces a solid salt, called a precipitate, from a liquid solution.

Oxidation

A chemical weathering process in which a mineral decomposes when it reacts with oxygen.

Hydrolysis

A chemical weathering process in which a mineral reacts with water to form a new mineral that has water as part of its crystal structure.

Dissolution

A chemical weathering process in which mineral or rock dissolves, forming a solution.

salt cracking

A chemical weathering process in which salts that are dissolved in water in the pores of rock crystallize, exerting an outward pressure on pore walls and pushing the mineral grains apart.

Dome

A circular or elliptical anticlinal structure resembling an inverted cereal bowl.

Shale

A clastic sedimentary rock that consists of lithified clay minerals and minor amounts of silt-sized quartz, feldspar, other minerals, and organic particles.

Conglomerate

A clastic sedimentary rock that consists of lithified gravel.

Stalagmite

A cone-shaped deposit of calcite formed over time as drops of water fall to the same spot on the floor of a cavern, release carbon dioxide gas upon impact, and precipitate the mineral as a result of the increase in pH.

Andean margin

A continental margin characterized by subduction of an oceanic lithospheric plate beneath a continental plate; also called a continental arc.

Meteor

A falling meteoroid that enters Earth's atmosphere and glows as it vaporizes; colloquially called a shooting star.

alluvial fan

A fan-shaped accumulation of sediment created where a steep mountain stream rapidly slows down as it reaches a relatively flat plain.

Delta

A fan-shaped accumulation of sediment formed where a stream enters a lake or ocean;

normal fault

A fault in which the hanging wall has moved downward relative to the footwall.

reverse fault

A fault in which the hanging wall has moved up relative to the footwall.

Syncline

A fold in rock that arches downward, and whose center contains the youngest rocks.

Anticline

A fold in rock that arches upward; the oldest rocks are in the middle.

liquid metallic hydrogen

A form of hydrogen under extreme temperature and pressure, which forces the atoms together so tightly that the electrons move freely throughout the packed nuclei, and as a result the hydrogen conducts electricity.

Creep

A form of mass wasting in which loose material moves very slowly downslope, usually at a rate of only about 1 centimeter per year and usually on land with vegetation. Trees on this type of block tilt downhill and grow to have a trunk shaped like a pistol butt.

Mudflow

A form of rapid mass wasting that involves the downslope movement, usually on unvegetated land, of fine-grained soil particles mixed with water; can be slow moving, as slow as 1 meter per year, or as fast as a speeding car.

Joint

A fracture along which the rock on either side of the break does not move. Compare with fault.

Fault

A fracture in rock along which one side has moved relative to the other side. Compare with joint

plate boundary

A fracture or boundary that separates two tectonic plates.

Crevasse

A fracture or crack in the brittle upper 40 meters of a glacier, formed when the glacier flows over uneven bedrock.

Landslide

A general term for mass wasting (the downslope movement of rock and regolith under the influence of gravity) and the landforms it creates.

island arc

A gently curving chain of volcanic islands in the ocean formed by the convergence of two plates, each bearing ocean crust, and the resulting subduction of one plate beneath the other

Great Red Spot

A giant hurricane-like storm on the surface of Jupiter that has existed for centuries.

U-shaped valley

A glacially eroded valley with a broad, characteristic U-shaped cross section.

ice sheet, or continental glacier

A glacier that covers an area of 50,000 square kilometers or more and spreads outward in all directions under its own weight.

alpine glacier

A glacier that forms in mountainous terrain.

travel-time curve

A graph in which first arrival times of P and S earthquake waves are plotted against distance from epicenter; the separation distance between the resulting two curves determines the distance between the seismograph location and the epicenter.

pluvial lakes

A lake formed in a topographic basin as the result of a moist climate during a glacial interval.

kettle lake

A lake that forms in a depression created by a receding glacier, filled with the water from the melting glacier.

karst topography

A landscape that forms over limestone or other soluble rock and is characterized by abundant sinkholes, disappearing streams, and caverns.

Icebergs

A large chunk of ice that breaks from a glacier into a body of water.

Caldera

A large circular depression created by the collapse of the magma chamber after an explosive volcanic eruption.

Batholith

A large pluton, exposed across more than 100 square kilometers of Earth's surface.

shield volcano

A large, gently sloping volcanic mountain formed by successive flows of basaltic magma.

Lake

A large, inland body of standing water that occupies a depression in the land surface.

soil horizons

A layer of soil that is distinguishable from other layers because of differences in appearance and in physical and chemical properties. Five soil horizons can occur: O, A, E, B, and C

Coquina

A limestone made up entirely of shell fragments

perched aquifer

A local aquifer formed where a layer of impermeable rock or sediment exists above the regional water table and creates a locally saturated zone.

subduction zone

A long, narrow region at a convergent boundary where a lithospheric plate is sinking into the mantle during subduction; also referred to as subduction boundary.

Esker

A long, snakelike ridge formed as the channel deposit of a stream that flowed within or beneath a melting glacier.

longitudinal dunes

A long, symmetrical dune that forms as a result of two different wind directions with comparable magnitude.

crescent moon

A lunar phase in which the Moon appears as a thin crescent, when either waxing or waning.

normal magnetic polarity

A magnetic orientation the same as that of Earth's current magnetic field.

Glacier

A massive, long-lasting accumulation of compacted snow and ice that forms on land and moves downslope or spreads outward under its own weight.

Competence

A measure of the largest particles that a stream can transport.

organic activity

A mechanical weathering process in which a crack in a rock is expanded by tree or plant roots growing there.

pressure-release fracturing

A mechanical weathering process in which tectonic forces lift deeply buried rocks upward and then erosion removes overlying rock and sediment—the net result of which is to remove the pressure from overlying material, causing the rock to expand and fracture.

frost wedging

A mechanical weathering process in which water freezes in a crack in rock, and the resulting expansion wedges the rock apart.

Abrasion

A mechanical weathering process that consists of the grinding and rounding of rock and mineral surfaces by friction and impact.

Thermal expansion and contraction

A mechanical weathering process that fractures rock when temperature changes rapidly, causing the surface of the rock to heat or cool faster, and thereby to expand or contract faster, than the rock's interior.

slaty cleavage

A metamorphic foliation producing a parallel fracture pattern that cuts across the original sedimentary bedding.

Meteorite

A meteor that does not completely vaporize and that strikes Earth's surface.

stony meteorite

A meteorite with a mass ratio of rock to metal similar to the mass ratio of Earth's mantle to Earth's core, thus reflecting the primordial composition of the Solar System and representing a window into its past. Most meteorites are this.

Heliocentric

A model that places the Sun at the center of the Solar System.

Ganymede

A moon of Jupiter marked by a convecting, metallic core and a brittle water/ice crust that behaves much like rock.

ground moraine

A moraine formed when a glacier recedes steadily and deposits till in a relatively thin layer over a broad area.

recessional moraine

A moraine that forms at the new terminus of a glacier as the glacier stabilizes temporarily during retreat.

Moraine

A mound or ridge of till deposited directly by glacial ice.

Dune

A mound or ridge of wind-deposited sand.

Stream

A moving body of water confined in a channel and flowing downslope; a river is a large version of this fed by smaller ones.

Mineral

A naturally occurring inorganic solid with a definite chemical composition and a crystalline structure.

lunar eclipse

A phenomenon that occurs when Earth lies directly between the Sun and the Moon, causing Earth's shadow to fall on the Moon and darken it.

solar eclipse

A phenomenon that occurs when the Moon passes directly between Earth and the Sun; the Moon casts its shadow on Earth, thus blocking the Sun's light.

divergent boundary

A plate boundary where tectonic plates move apart from each other and new lithosphere is continuously forming; also called a spreading center or a rift zone.

convergent boundary

A plate boundary where two tectonic plates move toward each other and collide.

transform boundary

A plate boundary where two tectonic plates slide horizontally past one another.

Stock

A pluton exposed over less than 100 square kilometers of Earth's surface; similar to a batholith, but smaller.

Salinization

A process whereby salts accumulate in soil that is irrigated heavily, lowering soil fertility.

Turnover

A process, occurring in fall and spring in temperate climates, in which a lake's surface water changes temperature in response to seasonal weather changes and convection mixes the water to equalize temperature throughout the lake.

flash flood

A rapid, intense, local flood of short duration, usually following a rainstorm.

Entisols

A very young soil typically lacking horizons and formed on unconsolidated parent material. All soils not classified with a different order are classified as this, so much diversity exists within this order.

Earthflow

A viscous flow of fine-grained sediment or fine-grained sedimentary rock that is saturated with water and moves downslope as a result of gravity; usually slow moving, typically less than one to several meters per day.

ash-flow tuff

A volcanic rock formed when a pyroclastic flow solidifies.

artificial levee

A wall built along the banks of a stream to prevent rising floodwater from spilling out of the channel onto the floodplain.

Exfoliation

A weathering process resulting in fracture when concentric plates or shells split away from a main rock mass like the layers of an onion; frequently explained as a form of pressure-release fracturing, but many geologists consider it could result from hydrolysis-expansion.

Graben

A wedge-shaped block of rock that has dropped downward between two normal faults, forming a valley.

artesian well

A well drilled into a confined aquifer, in which the water rises without pumping and in some cases flows to the surface.

Penumbra

A wide band outside of the umbra, where only a portion of the Sun is hidden from view during a solar eclipse.

Inceptisol

A young soil exhibiting weak horizons and developed in subhumid to humid environments. Typically retains abundant unweathered material.

San Andreas Fault zone

A zone of strike-slip faults extending from Cape Mendicino in northern California to the northern Gulf of California in Mexico; fault zone forms the transform boundary between the Pacific Plate and the North American Plate and is the source of many earthquakes.

cation exchange capacity (CEC)

Ability of a soil to release cations, typically by exchanging basic cations K+, Na+, Ca++, Mg++ for H+ from plant rootlets.

Horizontal Tectonics:

According to one model, early continents formed through the process of subduction. As plates converged, small continents (called protocontinents) collided and coalesced with volcanic arcs. Sediments eroded from the growing landmass were deposited, then folded and uplifted. Some were subjected to so much heat and pressure that they became metamorphic rocks. Magma was generated from partial melting of the crust at the subduction zone, forming new igneous rock.

Solid

All minerals are this. Thus, ice is a mineral, but neither water nor water vapor is a mineral.

Talus

An accumulation of loose, angular rocks at the base of a cliff, created as rocks broke off the cliff as a result of frost wedging.

fault zone

An area of numerous, closely spaced faults.

moment magnitude

An earthquake scale in which the surface area of fault movement is multiplied by an estimate of the faulted rock's strength; this scale closely reflects the total amount of energy released.

seismic waves

An elastic wave that travels through rock, produced by an earthquake or explosion.

terminal moraine

An end moraine that forms when a glacier is at its greatest advance before beginning to retreat.

pyroclastic flow

An extremely destructive incandescent mixture of volcanic ash, larger pyroclastic particles, minor lava, and hot gas that forms from collapse of an eruptive column and flows rapidly along Earth's surface.

Stalactite

An icicle-like dripstone of precipitated calcite that hangs from the ceiling of a cavern.

axial surface

An imaginary surface that connects all the points of maximum curvature in a fold.

confined aquifer

An inclined aquifer sandwiched between layers of impermeable rock; typically, the water in the lower part of the aquifer is under pressure from the weight of water above.

Seismograph

An instrument that records seismic waves.

Comet

An interplanetary orbiting body composed of loosely bound rock and ice, which forms a bright head and extended fuzzy tail when it approaches the Sun. It appears to be fiery hot, but it is actually a cold object and its "flame" is reflected light.

Vent

An opening in a volcano, typically in the crater, through which lava and rock fragments erupt.

Cavern

An underground cavity or series of chambers created when groundwater dissolves large volumes of rock, usually limestone; also called a cave.

sedimentary structures

Any feature of sedimentary rock formed by physical processes during or shortly after deposition; examples include stratification, cross-bedding, ripple marks, and tool marks.

geologic structure

Any feature produced by rock deformation, such as a fold or a fault; also refers to the combination of all such features in an area or region.

Parent rock

Any original rock before it is changed by weathering, metamorphism, or other geological processes.

biogenic structures

Any physical trace left in the sedimentary record by a fossil organism; includes tracks, trails, burrows, and root casts.

Drift

Any rock or sediment transported and deposited by a glacier or by glacial meltwater.

Magma Production in a Spreading Center

As lithospheric plates separate at a spreading center, hot, plastic asthenosphere oozes upward to fill the gap. As the asthenosphere rises, pressure drops and pressure-release melting forms magma with a basaltic composition. Because the magma is of lower density than the surrounding rock, it rises buoyantly toward the surface.

The Mantle below the Asthenosphere

At the base of the asthenosphere, the increasing pressure overcomes the effect of rising temperature, and the strength of the mantle increases again. Although the mantle below 350 kilometers is stronger than the asthenosphere, it is not as strong as the lithosphere, but rather is plastic and capable of flowing slowly over geologic time.

flood basalt

Basaltic lava that erupts gently and in great volume from vents or fissures at Earth's surface, to cover large areas of land and form lava plateaus.

Mohs hardness scale

Based on a series of 10 fairly common minerals and numbered 1 to 10 (from softest to hardest), used to measure and express the hardness of minerals.

Waxing

Becoming full; the 14 to 15 days after a new moon and before a full moon when the visible portion of the Moon increases every day.

Waning

Becoming smaller; the 14 to 15 days after a full moon and before a new moon when the visible portion of the Moon decreases every day.

Kuiper

Belt objects Tiny ice dwarfs, similar to Pluto, orbiting in a disk-shaped region at the outer reaches of the Solar System.

Carbonate rocks

Bioclastic sedimentary rocks composed of the carbonate minerals. Calcite-rich rocks are called limestone, whereas rocks rich in dolomite are referred to as dolomite or dolostone.

P waves

Body waves that travel faster than other seismic waves and are the first or "primary" waves to reach an observer; formed by alternating compression and expansion of rock parallel to the direction of wave travel.

Erratics

Boulders, usually different from bedrock in the immediate vicinity, that were transported to their present location by a glacier.

Fissures

Breaks, cracks, or fractures in rocks.

Till

Glacial drift that was deposited directly by glacial ice.

distributary channels

Channels that split from the main stream feeding a delta or alluvial fan and spread out across its surface, depositing sediment in the process.

Vertisol

Clay-rich, dark-colored soil characterized by periodic desiccation and deep cracking. Nearly impermeable and sticky when wet.

Inge Lehmann

Danish seismologist. 1936 Measured p-waves from earthquakes to determine there was a solid inner core surrounded by a liquid outer core. Not confirmed until 1970.

Downcutting

Downward erosion by a stream into its bed, usually by cutting a V-shaped valley along a relatively straight path.

maria

Dry, barren, flat expanses of volcanic rock on the Moon, first thought to be seas.

precession

Earth rotates, its axis wobbles like a spinning top in this type of motion

Alfred Wegener

German early 20th century. Theory of 'Continental Drift'. He explained it was caused by continents plowing through oceanic crust, or that continental crust slides over oceanic crust. Both reasons were proven wrong.

Drumlins

Elongate hills, usually occurring in clusters, formed when a glacier flows over and reshapes a mound of till or stratified drift.

Deflation

Erosion by wind.

Channel characteristics

Features describing the shape and roughness of a stream channel.

Flow

Form of rapid mass wasting in which loose soil or sediment moves downslope as a slurry-like fluid, not as a consolidated mass; may occur slowly (less than 1 centimeter per year for some earthflows) or rapidly (several meters per second for some mudflows and debris flows).

Slide

Form of rapid mass wasting in which the rock or soil initially moves as a consolidated unit along a fracture surface.

Fall

Form of rapid mass wasting in which unconsolidated material falls freely or bounces down steep slopes or cliffs.

Hardpan

General term for a soil layer that is relatively impervious to water and impenetrable to plant roots. Commonly forms from precipitation of salts in a soil B horizon either by downward or upward translocation.

Vesicles

Holes in lava rock that formed when the lava solidified before bubbles of gas or water could escape.

extrusive igneous rock

Igneous rock formed from material that has erupted through the crust onto the surface of Earth; usually finely crystalline. Also called volcanic rock.

Mud cracks

Irregular polygonal downward-tapering fractures that develop when mud dries; may be preserved when the mud is lithified.

Callisto

Jupiter's outermost Galilean moon; marked by a heavily cratered surface.

James Hutton

Late 1700's. Principles of gradualism and uniformitarianism.

Aa

Lava that has a jagged, rubbly, broken surface.

Pahoehoe

Lava with a smooth, billowy, or ropy surface.

Bedding

Layering that develops as sediments are deposited; also called stratification.

Litter

Leaves, twigs, and other plant or animal materials that have fallen to the surface of the soil but have not decomposed.

reversed magnetic polarity

Magnetic orientations in rock that are opposite to the current orientation of Earth's magnetic field.

Revolution

Orbiting around a central point. A satellite revolves around Earth, and Earth revolves around the Sun.

granite

Medium or coarsely crystalline igneous rock

pressure-release melting

Melting caused by a decrease in pressure, expansion of rock volume, and melting. Usually occurs in the asthenosphere.

native elements

Minerals that consist of only one element and thus the element occurs in the native state (not chemically bonded to other elements)

Carbonates

Minerals whose chemical composition is based on the carbonate anion ; an example is calcite .

Sulfides

Minerals whose chemical composition is based on the sulfide anion bonded to a metal cation; an example is pyrite .

Silicates

Minerals whose chemical elements include silicon and oxygen and whose crystal structures contain silicate tetrahedra.

magma

Molten rock generated from melting of any rock in the subsurface; cools to form igneous rock. Less dense so it rises to the surface.

basal slip

Movement of a glacier in which the entire mass slides over bedrock.

plastic flow

Movement of a glacier in which the ice flows as a viscous fluid.

Pluto

Once considered to be the ninth planet from the Sun in our Solar System, reclassified in 2006 as a dwarf planet.

glacial striations

Parallel grooves and scratches in bedrock that form as rocks are dragged along at the base of a glacier.

protolith

Parent rock of a metamorphic rock

Metamorphism

The process by which rocks change texture and mineral content in response to variations in temperature, pressure, chemical conditions, and/or deformation.

Nicholas Steno

Principle of original horizontality' - rock layers form in the horizontal position, and any deviations from this position are due to the rocks being disturbed later. 'Steno's law of superposition'- layers of rock are arranged in a time sequence, with the oldest on the bottom and the youngest on the top, unless later processes disturb this arrangement. 'Father of Stratigraphy'.

Wetlands

Regions that are water soaked or flooded for all or part of the year; includes swamps, bogs, marshes, sloughs, mudflats, and floodplains.

columnar joints

Regularly spaced cracks that commonly develop in lava flows, grow downward starting from the surface, and typically form five- or six-sided columns.

Sedimentary rock

Rock formed when sediment becomes compacted and cemented through the process of lithification.

pyroclastic rock

Rock made up of liquid magma and solid rock fragments that were ejected explosively from a volcanic vent.

igneous rock

Rock that forms when magma cools and crystallizes.

kame and kettle topography

Rolling hill topography associated with glacial kames and kettles.

spodosols

Sandy, acidic soil developed in moist, temperate environments, commonly in coniferous or mixed coniferous-deciduous forests. Leaching has translocated base cations downward, resulting in a well-developed E horizon.

Titan

Saturn's largest moon; the only moon in the Solar System with an appreciable atmosphere.

Alluvium

Sediment deposited by moving water.

Outwash

Sediment deposited by streams flowing from the terminus of a melting glacier.

Fossil Dunes

Sedimentary structures are common when sand dunes are buried and lithified over geologic time to become fossil dunes.

S waves

Seismic body waves that travel slower, and are the "secondary" waves to reach an observer; sometimes called shear waves due to the shearing motion in rock caused as the waves vibrate perpendicular to the direction they travel.

Surface waves

Seismic waves that radiate from the earthquake's epicenter and travel along the surface of Earth or along a boundary between layers within Earth.

Body waves

Seismic waves that travel through the interior of Earth, carrying energy from the earthquake's focus to the surface.

Vertical Mantle Plume Tectonics

Several researchers have proposed, instead, that mantle plumes dominated early Precambrian tectonics. In this view, upwellings of mantle rock led to partial melting in parts of the upper mantle. This magma then solidified to form basaltic crust. Continued partial melting eventually formed granitic continental crust.

Asteroids

Small celestial bodies in orbit around the Sun, primarily in the region between Mars and Jupiter.

Ripple marks

Small, sem-iparallel ridges and troughs formed mostly in sand by wind, water currents, or waves; often preserved when the sediment is lithified.

E horizon

Soil horizon in which organic acids derived from overlying O and A horizons leach soluble cations and translocate them downward along with clays.

sediment

Solid rock or mineral fragments that are transported and deposited by wind, water, gravity, or ice; that are weathered by natural forces, precipitated by chemical reactions, or secreted by organisms; and that accumulate in loose, unconsolidated layers.

Ultisols

Strongly weathered soil formed in semihumid or humid environments. Intense weathering has removed most base cations, resulting in low fertility. Includes red clay soils of SE United States.

blob tectonics

Tectonic activity dominated by rising and sinking of the mantle and crust, believed to predominate on Venus, as opposed to the horizontal movement of plates associated with tectonic activity on Earth.

spheroidal weathering

The combined mechanical and chemical weathering of fractured crystalline bedrock into spheroidally-shaped boulders; caused by the faster weathering rate of sharp bedrock corners (where at least three faces of rock can be attacked by weathering), over edges and the faster weathering of edges over faces.

Floodplain

That portion of a river valley adjacent to the channel; it is built upward by sediment deposited during floods and is covered by water during a flood.

Permeability

The ability of a solid material such as a rock to transmit water or another fluid through its pore network; depends on the size,shape, and interconnectedness of pores within the material.

lateral erosion

The action of a low-gradient stream as it cuts into and erodes its outer bank while simultaneously depositing sediment onto its inner bank; results in slow lateral migration of the channel and, through time, formation of wide, flat alluvial valleys.

Saltation

The asymmetric jumping movement of sedimentary particles that are ejected off the bed through impact by another particle and are carried downstream by wind or water for some distance before falling back to the bed surface.

orogen

The belt of rocks that is deformed in an orogeny.

Horst

The block of rock between two grabens, which has moved relatively upward along normal faults as the grabens have settled downward.

Mohorovičič discontinuity

The boundary between the crust and the mantle, identified by a change in the velocity of seismic waves; also called the Moho.

Thermocline

The boundary between the upper warm layers and deeper cool layers of water in a lake.

equilibrium altitude line, or ELA

The boundary between the zone of accumulation and the zone of ablation.

Coma

The bright outer sheath of a comet, surrounding the nucleus.

Transformation

The change of soil constituents from one form to another, such as the hydrolysis of feldspar to clay.

Crystal habit

The characteristic shape of an individual crystal, and the manner in which aggregates of crystals grow.

Leaching

The chemical dissolution of ions from the O and A soil horizons and their removal, usually downward into the B horizon where they accumulate.

Mercury

The closest planet to the Sun.

Streak

The color of the fine powder of a mineral, usually obtained by rubbing the mineral on an unglazed porcelain streak plate.

Humus

The dark, organic component of soil consisting of litter that has decomposed enough so that the origin of the individual pieces cannot be determined.

weathering

The decomposition and disintegration of rocks and minerals at Earth's surface by chemical and physical processes.

base level

The deepest level to which a stream can erode its bed. The ultimate is usually sea level.

Nucleus

The dense, solid core of a comet.

facing direction

The direction, up or down, in which a fold limb faces. In overturned and recumbent folds, one limb is facing down.

Slip

The distance that rocks on opposite sides of a fault have moved relative to each other.

Mass wasting

The downslope movement of earth material, primarily caused by gravity. (See also landslide.)

Playa

The dry desert lake bed of a playa lake.

Neptune

The eighth planet from the Sun; similar to Uranus in size, composition, and atmosphere.

pore space

The empty space between particles of rock, sediment, or soil.

Terminus

The end, or foot, of a glacier.

Prodelta

The fine-grained, outermost edge of a delta, located offshore beyond the delta front.

Bed

The floor of a stream channel.

terrestrial planets

The four Earth-like planets closest to the Sun—Mercury, Venus, Earth, and Mars—which are composed primarily of nonvolatile metals and silicate rocks.

Mars

The fourth planet from the Sun.

downhill creep

The gradual downhill movement, under the force of gravity, of soil and loose rock material on a slope. Facilitated by the freeze-thaw cycle, in which soil particles move orthogonal to the slope surface during freezing but directly downward during thawing.

zone of accumulation

The higher-altitude part of an alpine glacier where snow accumulates from year to year and forms glacial ice.

soil order

The highest hierarchical classification of soils by the National Resource Conservation Service. Twelve soil orders are recognized.

seafloor spreading

The hypothesis that segments of oceanic crust are separating at the Mid-Oceanic Ridge.

Fossils

The imprint, remains, or any other trace of a plant or animal preserved in rock.

Focus

The initial rupture point of an earthquake, typically located below Earth's surface.

Io

The innermost moon of Jupiter and the most active volcanic body in the Solar System.

metamorphic grade

The intensity of metamorphism that formed a rock; the maximum temperature and pressure attained during metamorphism.

Triton

The largest of Neptune's moons; marked by craters filled with ice or frozen methane.

Jupiter

The largest planet in the Solar System and fifth from the Sun

A horizon

The layer of soil below the O horizon, composed of a mixture of humus, sand, silt, and clay; combines with the O horizon to form topsoil.

zone of ablation

The lower-altitude part of an alpine glacier where more snow melts in summer than accumulates in winter, and where the melting snow leaves behind a surface of old, hard glacial ice.

soil series

The lowest hierarchical classification of soils by the National Resource Conservation Service. Over 20,000 are recognized, including 50 designated "state soils."

C horizon

The lowest soil layer, consisting of weathered bedrock.

new moon

The lunar phase during which the Moon is dark when viewed from Earth, because it has moved to a position between Earth and the Sun and its sunlit side faces away from us.

full moon

The lunar phase when the Moon appears round and fully illuminated, because it is on the opposite side of Earth from the Sun and its entire sunlit area is visible.

Fracture

The manner in which minerals break, other than along planes of cleavage.

Capacity

The maximum quantity of sediment that a stream can transport at any one time.

delta front

The more steeply sloping, usually submerged, outer edge of a delta beyond the delta top.

Loam

The most fertile soil, a mixture especially rich in sand and silt with generous amounts of organic matter.

Pleistocene Glaciation

The most recent series of glaciations occurring during the Pleistocene Epoch and beginning around 2 million years ago

Umbra

The narrow band of the Moon's shadow where the Sun is completely blocked out during a solar eclipse.

rock-forming minerals

The nine minerals or mineral groups that are most abundant in the Earth's crust and that combine to make most rocks. They are olivine, pyroxene, amphibole, mica, the clay minerals, quartz, feldspar, calcite, and dolomite.

Basement rock

The older igneous and metamorphic rock that lies beneath the thin layer of sedimentary rocks and soil covering much of Earth's surface; forms the base of the crust.

country rock

The older rock already in an area, cut into by a younger igneous intrusion or mineral deposit.

Aspect

The orientation of a slope with respect to the Sun; the direction toward which the slope faces.

Corona

The outer atmosphere of the Sun, normally invisible but appearing as a halo around a black Moon during a solar eclipse.

Jovian planets

The outer planets—Jupiter, Saturn, Uranus, and Neptune—all massive, with relatively small rocky or metal cores surrounded by swirling liquid and gaseous atmospheres.

Seismogram

The physical or digital record of earthquake waves as measured by a seismograph.

Epicenter

The point on Earth's surface directly above the initial rupture point (focus) of an earthquake.

Mid-Atlantic Ridge

The portion of the Mid-Oceanic Ridge system that lies in the middle of the Atlantic Ocean, halfway between North America and South America to the west, and Europe and Africa to the east.

Asthenosphere

The portion of the upper mantle just beneath the lithosphere, extending from a depth of about 100 kilometers to about 350 kilometers below the surface of Earth and consisting of weak, plastic rock where magma may form.

continental rifting

The process by which a continent is pulled apart at a divergent plate boundary.

subduction complex

The structurally complicated mass of rock consisting of deformed seafloor sediment and fragments of basaltic oceanic crust and upper mantle material that is scraped from the upper layers of the subducting slab in a subduction zone and added to the overriding plate.

Seismology

The study of earthquakes and the nature of Earth's interior based on evidence from seismic waves.

Inertia

The tendency of an object to resist a change in motion.

Cleavage

The tendency of some minerals to break along flat surfaces, which are planes of weak bonds in the crystal.

Regolith

The thin layer of loose, unconsolidated, weathered material that overlies bedrock. Some earth scientists and engineers use the term for this and soil interchangeably

water table

The top surface of the zone of saturation; separates the zone of saturation from the zone of aeration above.

suspended load

The total mass of a stream's sediment load that is carried within the flow by turbulence and is free from contact with the streambed.

bed load

The total mass of a stream's sediment load that is transported along the bottom or in intermittent contact with the bottom of the streambed.

dissolved load

The total mass of ions dissolved in and carried by a stream at any one time; the ions are derived from chemical weathering.

Mid-Oceanic Ridge system

The undersea mountain chain that forms at the boundary between divergent tectonic plates within oceanic crust. It circles the planet like the seam on a baseball, forming Earth's longest mountain chain.

delta top

The upper surface of a delta, including the parts above and below water.

O horizon

The uppermost layer of soil, named for its organic component; this combined with A Horizon is called topsoil.

Translocation

The vertical, usually downward, movement of physical or chemical soil constituents from one horizon to another.

Discharge

The volume of water flowing downstream over a specified period of time, usually measured in units of cubic meters per second (m3/sec) or cubic feet per second (cfs).

Specific gravity

The weight of a substance relative to the weight of an equal volume of water.

metamorphic halo

The zone surrounding an intrusive igneous body in which the country rock has been metamorphosed by heat and hydrothermal fluids from the cooling magma.

Tillite

Till that was deposited by glaciers so long ago that it became lithified into solid rock.

Recharge

To replenish an aquifer by the addition of water.

Rotation

Turning or spinning on an axis. Tops and planets rotate on their axes.

obsidian

Volcanic glass. Because the magma hardens so quickly, the atoms have no time to align themselves to form crystals. As a result, the atoms are frozen into a random chaotic pattern, as happens in glass.

Catastrophism

Whewell - occasionally huge catastrophes have altered the course of Earth History

Andisol

Young soil developed on volcanic parent material and containing abundant unweathered volcanic glass and other volcanic debris, resulting in a high cation exchange capacity and high fertility.

fold

a bend in rock. Some of these rocks display little or no fracturing, indicating that the rocks deformed in a plastic manner.

extrusion

a body of magma that cools on Earth's surface

heat of fusion

a certain amount of heat is needed simply to melt ice and produce its phase change from solid to liquid.

Basalt

a common, very finely crystalline volcanic rock. consists of approximately equal amounts of plagioclase feldspar and pyroxene. It makes up most of the oceanic crust, as well as huge plateaus on continents.

Microcrystalline texture

a fine-grained aggregate of inter-grown microscopic crystals. The rock may appear either smooth or sugary.

Slaty cleavage

a flat foliation developed along parallel planes. typically are rich in clay or mica, lack observable crystals.

element

a fundamental component of matter that cannot be broken into simpler particles by ordinary chemical processes.

Recrystallization

a process whereby numerous, small mineral crystals of the protolith convert to fewer, larger crystals in the metamorphic rock.

Mantle plume

a relatively small rising column of plastic mantle rock that is hotter than surrounding rock. Some appear to rise from great depths in the mantle, probably because small zones of rock near the core-mantle boundary become hotter and more buoyant than surrounding regions of the deep mantle. Others form as a result of heating in shallower portions of the mantle.

Continental drift

a single supercontinent (pangea) broke apart to form the modern continents.

Phyllite texture

a wavy or wrinkled foliation of fine-grained crystals. typically have a satiny or metallic luster

Hot spot

as pressure decreases in a rising plume, rock melts to form magma. The rising heat and magma produce a hot spot in the upper mantle which in turn heats the overlying lithosphere, forming a volcanic center.

Contact metamorphism

associated with igneous intrusions and with fractures in contact with hydrothermal (hot) fluids. occurs locally and in conditions of intense heat and low to medium pressures. Zones of this are narrow and in close association with magma or hydrothermal fluids.

Magma Production in a Mantle Plume

at a mantle plume is a rising column of hot, plastic rock that originates within the mantle. The plume rises because it is hotter than the surrounding mantle and, consequently, is less dense and more buoyant. As a plume rises, pressure-release melting forms magma, which continues to rise toward Earth's surface

Regional Dynamothermal Metamorphism

ccurs where major crustal movements build mountains and deform rocks. the rocks are being deformed and heated at the same time. It is the most common and widespread type of metamorphism and affects broad regions of Earth's crust.

Travertine

chemical limestone, is a sedimentary rock composed of crystalline CaCO3 formed by the chemical precipitation of groundwater from hot or cold springs, or on the walls of caves.

plutonic

coarsely crystalline

chert

common organic sedimentary rock. is composed of very finely-crystalline quartz.

Clastic sedimentary rock

composed of particles of weathered rocks, such as sand grains and pebbles, called clasts, which have been transported, deposited, and lithified. (The generic term clastic refers to any rocks that are composed of fragments of older rocks.) This category includes conglomerate, sandstone, and shale. makes up about 85 percent of all sedimentary rock.

Organic sedimentary rock

consists of the lithified remains of plants or animals. Coal is this, and it contains such a high percentage of decomposed and compacted plant remains that the rock itself will burn.

Dolostone

contains dolomite (CaMg(CO3)2) mineral crystals that are usually microcrystalline, and are formed through the alteration of limestone.

Mantle convection

continually stirs the entire mantle as rock that is hotter than its surroundings rises toward Earth's surface and old plates that are colder than their surroundings sink into the mantle. Generated by heat from the core below, radioactive decay of unstable isotopes within the mantle, and the cooling of the upper surface that is in contact with the lithosphere.

Glassy texture

homogeneous with no visible grains or structures along glossy surfaces.

rhyolite

igneous rock is very finely crystalline

Bowen's Reaction Series

illustrates the progression of mineral crystalliza-tions produced by cooling magma.

Albedo

is a general term that refers to the reflectivity of sunlight. Things with low levels of this, tend to absorb heat well, such as forests. High level materials, such as snow and ice, reflect sunlight and thus absorb very little heat.

Gabbro

is the plutonic equivalent of basalt; it is mineralogically identical but consists of larger crystals. is uncommon at Earth's surface, although it is abundant in deeper parts of the oceanic crust, where basaltic magma crystallizes slowly.

The Mantle

lies directly below the crust. It is almost 2,900 kilometers thick and makes up percent of Earth's volume. composed mainly of peridotite, a rock that is denser than the basalt and granite of the crust.

Non-foliated

metamorphic rocks lack layers or cleavage planes, and may be produced by either regional or contact metamorphism.

Schistosity

n alignment of visible platy minerals and/or long prismatic crystals. break along foliations

bedded chert

occurs as sedimentary beds or layers

Contact Metamorphism

occurs where hot magma intrudes cooler rock of any type—sedimentary, metamorphic, or igneous. The highest grade metamorphic rocks form at the contact point, closest to the magma. Lower-grade rocks develop farther away.

reaction to acid test

performed to identify carbonate (CaCO3) minerals such as calcite or dolomite. Carbonate reacts with acid to form carbon dioxide gas (CO2), water, dissolved calcium (Ca+2), and dissolved chlorine (Cl-).

Arthur Holmes

pioneered radioactive dating to determine age of minerals. Determined the age of the earth was much bigger than thought before. Initially considered it 1.6 billion y.o., but landed on 4.5 billion. Also suggested the mechanism for Continental Drift was that the plates rested on and shifted across the top of the mantle.

Burial Metamorphism

results from the burial of rocks in a sedimentary basin. Younger sediment may bury the oldest layers to depths greater than 10 kilometers in a large basin. Over time, temperature and pressure increase within the deeper layers until burial metamorphism begins.

Mafic minerals

rich in magnesium, calcium, and iron and are darkly colored.

Felsic minerals

rich in silica, sodium, and potassium and are lightly colored.

Magma Production in a Subduction Zone

the addition of water, decreasing pressure, and heat from friction all combine to form huge quantities of magma. A subducting plate is covered by water-saturated oceanic sediments, and the upper portions of the underlying basalt also are saturated with water. As the wet rock and sediments dive into the hot mantle, the heated water ascends into the hot asthenosphere directly above the sinking plate.

Gneissic banding

the alternating layers of light and dark, medium- to coarse-grained crystals. typically rich in quartz

Metasomatism

the chemical alteration of a rock through fluid interaction.

Convection

the circulating flow of fluid material in response to heating and cooling.

crystal form

the geometric shape of a single crystal, bounded by flat crystal faces that intersect at specific angles. Classified into six systems: isometric, tetragonal, orthorhombic, hexagonal, monoclinic, and triclinic.

The Core

the innermost of Earth's layers. It is a sphere with a radius of about 3450 kilometers, about the same size as Mars, and is composed largely of iron and nickel. The outer core is molten because of the high temperature and relatively lower pressure there. In contrast, the temperature of the inner core is close to 7000 Degrees C, roughly similar to the temperature of the Sun's surface, and the pressure is 3.4 million times that of Earth's atmosphere at sea level. This extreme pressure compresses the inner section to a solid, despite the fact that it is even hotter than the molten outer section.

Color

the most obvious property of a mineral, and it is often used in identification. But can be unreliable, because small amounts of chemical impurities and imperfections in crystal structure can dramatically alter it.

Lithosphere

the outer part of Earth, including both the crust and the uppermost mantle. consists mostly of the cold, strong uppermost mantle; the crust is just a thin layer of buoyant rock forming the top of this.

The Crust

the outermost and thinnest layer. Because it is cool relative to the layers below, consists of hard, strong rock

mafic color index (MCI)

the percentage of its green, dark gray, and black mafic mineral crystals.

Mechanical weathering

the physical break down of rocks to form clasts by natural forces, such as rain, snow, wind, and ice. The disintegration of rock into smaller pieces by physical processes without altering the chemical composition of the rock.

soil

the upper layers of regolith.