Earth Science Glossary
(Most definitions taken from Earth Science 11e)
(Last update - July 27, 2008)
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§
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 reef – A 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 reef – A 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 |