CHAPTER 9 DEFINITIONS
geologic column – an ordered arrangement of rock layers that is based on the relative ages of the rocks and in which the oldest rocks are at the bottom
era – a unit of geologic time that includes two or more periods
period – a unit of geologic time that is longer than an epoch but shorter than an era
epoch – a subdivision of geologic time that longer than an age but shorter than a period
evolution – a heritable change in the characteristic within a population from one generation to the next; the development of new types of organisms from preexisting types of
organisms over time
Precambrian time – the interval of time in the geologic time scale from Earth’s formation to the beginning of the Paleozoic era, from 4.6 billion to 542 million years ago
Paleozoic era – the geologic era that followed Precambrian time and that lasted from 542 million to 251 million years ago
mass extinction – an episode during which large numbers of species became extinct
Mesozoic era – the geologic era that lasted from 251 million to 65.5 million years ago, also called the Age of Reptiles
Cenozoic era – the current geologic era, which began 65.5 million years ago; also called the Age of Mammals
geologic time scale – a scale that outlines the development of Earth and of life on Earth that is recorded in the rock layers of Earth’s crust
mega-annum – abbreviated “Ma” which means one million years
eon – the largest unit of geologic time
nebula – a large cloud that is said to be the beginning of the formation of Earth
ages – smaller units of time that are divisions of epochs
shields – large areas of exposed Precambrian rocks that are found on every continent
invertebrates – animals that do have a backbone
index fossils – a fossil that is used to establish the age of a rock layer because the fossil is distinct, abundant, widespread and existed for only a short span of geologic time
vertebrates – animals that have a backbone
Age of Fishes – reference to the Mesozoic era because conditions favored the survival of reptiles
impact hypothesis – a hypothesis that about 65 million years ago, a giant meteorite crashed into the Earth causing a mass extinction at the end of the Cretaceous period
Age of Mammals – reference to the Cenozoic era because mammals became the dominant life form
Tertiary period – the Paleocene, Eocene, Oligocene, Miocene and Pliocene Epochs that lasted 65.5 million to 1.8 million years ago
Quaternary period – the Pleistocene and Holocene Epochs that lasted from 1.8 million years ago to present day
CHAPTER 10 DEFINITIONS
continental drift – the hypothesis that states that the continents once formed a single landmass, broke up and drifted to their present location
supercontinent – a single landmass
mid-ocean ridge – a long, undersea mountain that has a steep, narrow valley at its center, that forms as magma rises from the asthenosphere and that creates new oceanic
lithosphere as tectonic plates move apart
rift – a crack in Earth’s crust located at the center of a ridge
magma – molten rock located beneath Earth’s surface
sea-floor spreading – the process by which new oceanic lithosphere forms as magma rises to Earth’s surface and solidifies at a mid-ocean ridge
paleomagnetism – the study of the alignment of magnetic minerals in rock, specifically as it relates to the reversal of Earth’s magnetic poles; also the magnetic properties that
rock acquires during formation
normal polarity – rocks with magnetic fields that point North
reversed polarity – rocks with magnetic fields that point South
geomagnetic reversal time scale – the placing of period of normal and reversed polarity in chronological order to form a pattern of alternating normal and reversed polarity in
rocks
plate tectonics – the theory that explains how large pieces of the lithosphere called plates move and change shape
lithosphere – the solid, outer layer of Earth that consists of the crust and the upper, rigid part of the mantle
tectonic plates – large, individual blocks of the lithosphere that rides on the asthenosphere
asthenosphere – the solid, plastic layer of the mantle beneath the lithosphere; made of mantle rock that very slowly, which allows tectonic plates to move on top of it
oceanic crust – lithosphere that is dense and is made of rock rich in iron and magnesium
continental crust – lithosphere that has a low density and is made of rock that is rich in silica
earthquake – a movement or trembling of the ground that is caused by a sudden release of energy when rocks along a fault move
divergent boundary – the boundary between tectonic plates that are moving away from each other
convergent boundary – the boundary between tectonic plates that are colliding
subducts – the sinking of one plate under another plate due to the differences in density
subduction zone – an area along a convergent boundary where one plate subducts under another plate
island arc – a string of volcanic islands that form along a subduction zone
transform boundary – the boundary between tectonic plates that are sliding past each other horizontally
fracture zone – short segments of a mid-ocean ridge that are connected by a transform boundary
convection – movement of heated materials due to differences in density that are caused by differences in temperature
convection cell – a cycle of hotter, less dense material rising and cooler, more dense material sinking
ridge push – a force exerted on a plate by the asthenosphere caused by the sinking of cooling rocks of the lithosphere
slab pull – the force exerted on a plate that results in the pulling of the plates as it subducts into the asthenosphere
craton – large area of stable rock located on all continents
shields – cratons that have been exposed at Earth’s surface
rifting – the process by which Earth’s crust breaks apart; can occur within continental or oceanic crust
terrane – a piece of lithosphere that has unique geologic history and that may be part of a larger piece of lithosphere, such as a continent
accretion – the process in which a terrane becomes part of a continent
sea mounts – underwater mountains that may become a terrane
atolls – small coral islands that may be terranes
supercontinent cycle – the process by which supercontinents form and break apart over millions of years
Pangaea – the supercontinent that formed 300 million years ago and that began to break up 250 million years ago.
Panthalassa – the single, large ocean that covered Earth’s surface during the time Pangaea existed
Laurasia – one of two continents that formed from the break up of Pangaea and contained North America, Europe and Asia
Gondwanaland - one of two continents that formed from the break up Pangaea and contained India, Africa South America, Australia and Antarctica
CHAPTER 11 DEFINTIONS
deformation – the bending, tilting and breaking of Earth’s crust; the change in shape or volume of rock in response to stress
asthenosphere – plastic part of the mantle
isostacy – a condition of gravitational and buoyant equilibrium between Earth’s lithosphere and asthenosphere
isostatic adjustments – the movements of the lithosphere to reach isostacy
uplift – the upward movement of the lithosphere as a result of weathering of mountains
subsidence – sinking of the ocean floor in reaction to the added weight of deposited sediments
stress – the amount of force per unit area that acts on rock
compression – a stress that squeezes and shortens a body commonly reducing the amount of space that rock occupies
tension – stress that stretches and pulls a body apart and tends to cause rocks to become thinner
shear stress – distorts a body by pushing parts of the body in opposite directions and is common at transform boundaries
strain – any change in a rock’s shape or volume caused by stress
brittle – materials that respond to stress by breaking or fracturing
ductile – materials that respond to stress by bending or deforming without breaking
fold – a form of ductile strain in which rock layers bend, usually as a result of compression
limbs – sloping sides of a fold
hinge – the bend in the rock where limbs meet
axial plane – a plane that can separate a fold into two symmetrical halves
overturned – a term to describe a fold that appears to be lying on its side
anticline – a fold in which the oldest layer is in the center of the fold
syncline – a fold in which the youngest layer is in the center of the fold
monocline – a fold in which the limbs are horizontal or almost horizontal
ridge – a large, narrow strip of elevated land that can occur near mountains
fracture – a break along which there is no movement of the surrounding rock
fault – a break in a body of rock along which one block slides relative to another; a form of brittle strain
fault plane – the surface or plane along which the motion occurs in fault
hanging wall – the rock above the fault plane
footwall – the rock below a fault plane
normal fault – a fault in which the hanging wall moves downward relative to the footwall
reverse fault – a fault in which the hanging wall moves upward relative to the footwall
thrust fault – a special type of reverse fault in which the fault plane is at a low angle or nearly horizontal
strike-slip fault – the rock on either side of the fault plane slide horizontally in response to shear stress
slip – the sliding of rocks past each other
strike – the length of the fault
mountain range – a series of mountains that are closely related in orientation, age, and mode of formation
mountain system – a group of mountain ranges that are adjacent
mountain belts – two larger systems that encompass the largest mountain systems
terrane – pieces of lithosphere that are scraped off of oceanic lithosphere at convergent boundaries that become mountains on continental lithosphere
folded mountains – a mountain that forms when rock layers are squeezed together and uplifted
plateau – large, flat areas of rock high above sea level
fault-block mountain – a mountain that forms where break Earth’s crust into large blocks and some blocks drop down relative to other blocks
graben – long, narrow valleys that develop when steep faults break the crust into blocks and one block slips downward relative to other blocks
dome mountain – a circular or elliptical, almost symmetrical elevation or structure in which the stratified rock slopes downward gently from the central point of folding
volcanic mountain – mountain that forms when magma erupts onto Earth’s surface and commonly form along convergent boundaries
hot spot – a volcanically active are of Earth’s surface, commonly far from tectonic plate boundaries
CHAPTER 12 DEFINITIONS
earthquake – a movement of the ground that is caused by the sudden release of energy when rocks move along a fault
fault – a break in a body of rock along which one block slides relative to another
locked – an immobile state of a fault due to the presence of friction between the plates
elastic rebound – the sudden return of elastically deformed rock to its undeformed state
rebound – the springing back of rock after they separate at their weakest point
focus – the location within Earth along a fault which the first motion of an earthquake occurs
epicenter – the point on Earth’s surface directly above an earthquake’s starting point or focus
seismic waves – vibrations in or on the Earth caused when rocks release energy as a result of slipping into new positions
body wave – a seismic wave that travels through the body of a medium
surface wave – a seismic wave that travels along the surface of a medium
P wave – a seismic wave that causes particles of rock to move in a back-and-forth direction parallel to the direction in which the wave is traveling. The fastest moving seismic
wave and can travel through solids, liquids and gases
primary wave – another name for a P wave or a compression wave
compression wave – another name for a P wave or a primary wave
S wave – a seismic wave that causes particles of rock to move in a side-to-side direction perpendicular to the direction in which the wave is traveling; second fastest seismic
wave and can only travel through solids
secondary wave – another name for an S wave or shear wave
shear wave – another name for an S wave or secondary wave
Love wave – surface wave that causes the rock to move side-to-side and perpendicular to the direction in which the wave is traveling
Rayleigh wave – surface wave that causes the ground to move with an elliptical, rolling motion
shadow zone – an area on Earth’s surface where no direct seismic waves from a particular earthquake can be detected
fault zone – a region of numerous, closely space faults
seismology – the study of earthquakes and seismic waves
seismograph – an instrument that records vibrations in the ground
seismogram – a tracing of earthquake motion that is recorded by a seismograph
magnitude – a measure of the strength of an earthquake
Richter scale – a scale used to measure the ground motion from an earthquake to find the earthquake’s strength
moment magnitude – a measurement of earthquake strength based on the size of the area of the fault that moves, the average distance that the fault blocks move and the
rigidity of the rock’s in the fault zone
intensity – the amount of damage caused by an earthquake
Mercalli scale – a modified scale that expresses intensity in Roman numerals from I to XII and provides a description of the effects of each earthquake intensity
tsunami – a giant ocean wave that forms after a volcanic eruption, submarine earthquake or landslide
seismic gap – an along a fault where relatively few earthquakes have occurred recently, but where strong earthquakes are known to have occurred in the past
foreshock – little earthquakes that precede a major earthquake are of Earth’s surface, commonly far from tectonic plate boundaries
CHAPTER 13 DEFINITIONS
magma – liquid rock produced under Earth’s surface
volcanism – any activity that includes the movement of magma toward or onto Earth’s surface
lava – liquid rock located on Earth’s surface
vent – an opening in Earth’s lithosphere through which magma flows
volcano – a vent or fissure in Earth’s surface through which magma and gases are expelled
subduction – an area along a convergent boundary where one plate sinks beneath another plate
trench – a long, narrow and steep depression that forms in the ocean floor as a result of subduction of a tectonic plate, that runs parallel to the trend of a chain of volcanic
islands or the coastline and that may be as deep as 11km below sea level
island arc – a string of volcanic islands that form along a subduction zone
fissures – cracks through which lava flows to Earth’s surface
hot spot – a volcanically active area of Earth’s surface, commonly far from tectonic plate boundaries
mantle plume – columns of solid, hot material from the mantle
intrudes – magma that comes into contact with overlying rock
igneous rock – rock that forms from solidified magma or lava
pluton – magma that cools inside Earth’s crust and results in large formations of igneous rock
dike – magma that forces through rock layers by following existing vertical fractures and then solidifies
batholiths – large pluton that covers an area of at least 100 km2 when exposed at Earth’s surface
mafic – magma or igneous rock that is rich in magnesium and iron and that is generally dark in color
felsic – magma or igneous rock that is rich in feldspar and silica and that is generally light in color
viscosity – used to describe a fluid’s resistance to flow
pahoehoe – forms from hot, fluid lava that forms a smooth, ropy texture on the surface as it cools
aa – lava whose crust deforms rapidly or grows too thick to from wrinkles, the surface breaks into chunks
blocky lava – highly viscous lava that causes the surface to break into large chunks as the surface cools while the hot lava underneath continues to flow
pyroclastic material – fragments of rock that form during a volcanic eruption
volcanic ash – pyroclastic particles that are smaller than 22mm but larger than 0.25mm in diameter
volcanic dust – pyroclastic particles that are smaller than 0.25mm in diameter
lapilli – a Latin term that means “little stones” which is pyroclastic particles that are smaller than 64mm in diameter
volcanic bombs – large clots of lave that are thrown from the vent and spin in the air and develop a round or spindle shape as they cool
volcanic blocks – the largest pyroclastic material forms from solid rock that is blasted from the vent and may be as large as a small house
crater – the funnel-shaped pit at the top of a volcanic vent
caldera – a large, circular depression that forms when the magma chamber below a volcano partially empties and causes the ground above to sink
CHAPTER 14 DEFINITIONS
weathering – the natural process by which atmosphere and environmental agents, such as wind, rain and temperature changes, disintegrate and decompose rock
mechanical weathering – the process by which rocks break down into smaller pieces by physical means
joints – long, curved cracks in rocks
exfoliation – the process by which rock breaks into curved sheets that peel away from underlying rock because joints are parallel to the surface of the rock
ice wedging – process of mechanical weathering where water seeps into cracks of rock and freezes increasing the volume of water causing the cracks to increase in size and
eventually breaking the rock into smaller pieces
abrasion – the grinding and wearing away of rock surfaces through the mechanical action of other rock or sand particles
chemical weathering – the process by which rock breaks down as a result of chemical reactions
oxidation – the process by which a metallic element combines with oxygen
hydrolysis – a chemical reaction between water and another substance to form two or more new substances
leaching – carrying of dissolved minerals to lower layers of rock by water
carbonation – the conversion of a compound into a carbonate
acid precipitation – precipitation that contains a high concentration of acids, often because of the pollution of the atmosphere
differential weathering – the process by which softer, less weather resistant rocks wear away at a faster rate than arder, more weather resistant rocks
surface area – the part of the rock that is exposed to air, water and other agents of weathering
topography – the size and shape of the land surface features of a region, including its relief
regolith – layer of weathered rock fragments that cover much of Earth’s surface
bedrock – solid, unweathered rock that lies beneath the regolith
soil – loose mixture of rock fragments and organic material that can support the growth of vegetation
parent rock – the original rock from which the soil was weathered
residual soil – soil that is directly over the parent rock it formed from
transported soil – soil that is transported away from its parent rock
soil profile – a vertical section of soil that shows the layer of horizons
horizon – a horizontal layer of soil that can be distinguished from the layers above and below it
A horizon (topsoil) – a mixture of organic materials and small rock particles and the zone from which water leaches minerals
humus – dark, organic material formed in soil from the decay of remains of plants and animals
B horizon (subsoil) – contains minerals leached from the topsoil, clay and sometimes humus, may also contain minerals that accumulate as water in the soil evaporates
C horizon – consists of partially weathered bedrock
laterites - thick, tropical soils that contain iron and aluminum minerals that do not dissolve easily in water
pedalfer – soil that contains clay, quartz and iron compounds and is found in areas that receive more than 65cm of rain per year
pedocal – soil that contains large amounts of calcium carbonate, which makes the soil very fertile and less acidic and is found in areas that receive less than 65cm of rain per year
erosion – a process in which the materials of Earth’s surface are loosened, dissolved or worn away and transported from one place to another by a natural agent such as wind,
water, ice or gravity
gullying – a process of accelerated erosion caused by the plowing of furrows up and down slopes allowing for rainfall to wash away the soil
sheet erosion – the process by which water flows over a layer of soil and removes the topsoil
fertile soil – soil that can support the growth of healthy plants
land degradation – human activity and natural processes that damage the land to the point that it can no longer support the local ecosystem
urbanization – the movement of people from rural areas to cities that may lead to land degradation
overgrazing – a process that occurs when more animals are allowed to graze an area than the plants in the area can support
deforestation – a process of clearing of trees from an area without replacing them
desertification – a process by which land in dry areas become more desert like because of human activity or climate change
contour plowing – soil is plowed in curved bands that follow the contour, or shape of the land
strip-cropping – a process in which crops are planted in alternating bands with a cover crop planted in between
cover crop – a crop that is planted in between the main crop in strip-cropping and covers the soil completely reducing the amount of soil erosion
terracing – the construction of step-like ridges that follow the contours of sloped field
crop rotation – farmers plant one type of crop one year and a different crop the next
mass movement – the movement of a large mass of sediment or a section of land down a slope
rockfall – the fasted kind of mass movement that occurs when rocks fall from a steep cliff
landslide – a process in which masses of loose rock combined with soil suddenly fall down a slope
mudflow – the rapid movement of a large amount of mud and generally occurs in dry, mountainous regions during sudden, heavy rainfall or as a result of volcanic eruptions
slump – a process in which a large block of soil and rock becomes unstable and moves downhill in one piece usually occurring along very steep slopes
solifluction – the slow, downslope flow of soil saturated with water in areas surrounding glaciers at high elevations
creep – the extremely slow, downhill movement of weathered rock material
talus – an accumulation of rock fragments at the base of a slope
landform – a physical feature on Earth’s surface
peneplains – a low, featureless surface formed from mountains that are no longer being uplifted and occurs over millions of years
plain – a relatively flat landform near sea level
plateau – a broad, flat landform that has a high elevation
mesa – a landform that is formed when a plateau ages and erosion dissects the plateau into smaller, table-like areas
buttes – landforms that form when mesas erode to small, narrow-topped formations
CHAPTER 15 DEFINITIONS
water vapor – water in the atmosphere in gaseous form
water cycle – the continuous movement of water between the atmosphere, the land and the oceans
evaporation – the process by which water turns to vapor at the surface of the liquid
transpiration – the process by which plants release water vapor into the atmosphere
evapotranspiration – the total loss of water from an area which the sum of the water lost by evaporation and the water lost by transpiration
condensation – the change of state from a gas to a liquid
precipitation – any from of water that falls to Earth’s surface from the clouds; includes, rain, snow, sleet and hail
water budget – the total amount of water coming in and going out
local water budget – the water budget of a given area
desalination – a process of removing salt from ocean water
gully – a narrow ditch that is formed as rain runoff erodes rock and soil
tributaries – a stream that flows into a lake or into a larger stream
watershed – the area of land that is drained by a river system
divides – ridges or elevated regions that separate watersheds
channel – the relatively narrow depression that a stream follows as it flows downhill
banks – the edges of a stream channel that are above water level
bed – the part of the stream channel that is below the water level
headward erosion – the process in which channels lengthen and branch out at the upper ends, where runoff enters the streams
stream piracy – a process in which a stream from one watershed is “captured” by a stream from another watershed that has a higher rate of erosion
stream load – the materials other than water that are carried by a stream
suspended load – particles of fine sand and silt that are suspended in the stream by the stream’s velocity
bed load – larger, coarser materials located at the bed of a stream and move by sliding and jumping along the bed
dissolved load – mineral matter transported in liquid solution of the stream
discharge – the volume of water that flows within a given time
gradient – the change in elevation over a given distance
headwaters – the beginning of a stream
mouth – the part of the stream that enters a larger body of water
river – a stream that becomes larger and wider over time as a result of erosion
meander – one of the bends, twists or curves in a low gradient stream or river
bar – deposited sediment on the inside curve of a river that forms because of a decrease of stream velocity
oxbow lake – a crescent shaped lake that forms as a result of a river that cuts across a narrow neck and the meander becomes isolated from the river
braided stream – a stream or river that is composed of multiple channels that divide and rejoin around sediment bars
delta – a fan-shaped mass of rock material deposited at the mouth of a stream
alluvial fan – a fan-shaped mass of rock material deposited by a stream when the slope of the land decreases sharply
floodplain – an area along a river that forms from sediments deposited when a river overflows its banks
natural levee – the accumulation of deposited sediment along the banks of a channel are a result of a stream losing velocity as it overflows its banks and spreads out
dam – an artificial structure built to control flooding and create an artificial lake
artificial levee – an artificial structure built along the banks of a stream or river to prevent flooding and overflowing of the stream or river
CHAPTER 16 DEFINITIONS
pores – spaces or openings in rock particles
groundwater – the water that is beneath Earth’s surface
aquifer – a body of rock or sediment that stores groundwater and allows the flow of groundwater
porosity – the percentage of the total volume of rock or sediment that consists of open spaces
sorting – the amount of uniformity in the size of the rock or sediment particles shows
permeability – the ability of rock or sediment to let fluids pass through
impermeable – the inability of rock or sediment to let fluids pass through
zone of saturation – the layer of an aquifer in which the pore space is completely filled with water
saturated – a term to describe that the pores and spaces of rock are filled to capacity with water
water table – the upper surface of underground water; the upper boundary of the zone of saturation
zone of aeration – the zone that lies between the water table and Earth’s surface
capillary fringe – the process of drawing water up from the zone of saturation into the capillary fringe caused by the adhesion of water molecules to other materials
gradient – the steepness of a slope
perched water table – water that collects above an impermeable layer that is located above the water table and creates a second water table
recharge zone – anywhere that water from the surface can travel through permeable rock to reach an aquifer
well – a hole that is dug to below the level of the water table and through which groundwater is brought to Earth’s surface
spring – a natural flow of groundwater to Earth’s surface in places where the ground surface dips below the water table
artesian formation – a sloping layer of permeable rock sandwiched between two layers of impermeable rock and exposed at the surface
caprock – the top layer of impermeable rock in an artesian formation
artesian well – a well through which water flows without being pumped
artesian spring – a formation that forms when water flows from an aquifer through natural cracks in the caprock
hot spring – groundwater that is at 37 oC and rises to Earth’s surface before cooling
travertine – step-like terraces of calcite that form when minerals are deposited when hot springs cool
mud pots – from when chemically weathered rock mixes with hot water to form a sticky, liquid clay that bubbles at the surface
paint pots – forms when the clay in mud pots is brightly colored by minerals or organic material
geysers – hot springs that periodically erupt from surface pools or through small vents
hard water – water that contains relatively high concentrations of dissolved minerals
soft water – water that contains relatively low concentrations of dissolved minerals
cavern – a natural cavity that forms in rock as a result of the dissolution of minerals; also a large cave that commonly contains many smaller, connecting chambers
stalactite – a suspended, cone-shaped deposit of calcite hanging from the ceiling of a cavern
stalagmite – an upward-pointing cone of calcite that forms on the floor of a cavern
column – a calcite deposit that forms when a stalactite and stalagmite meet to form a single calcite deposit
sinkhole – a circular depression that forms when rock dissolves, when overlying sediment fills an empty cavity or when the roof of an underground cavern or mine collapses
collapse sinkhole – a sinkhole that forms when sediment below the surface is removed and an empty space forms within the sediment causing the overlying sediment to collapse
into the empty space
subsidence sinkhole – forms as rock dissolves, overlying sediments fill the cracks in the rock and a depression forms
natural bridge – the uncollapsed rock between each pair of sinkholes forming an arch or rock
Karst topography – a type of irregular topography that is characterized by caverns, sinkholes and underground drainage and the forms on limestone or other soluble rock