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 magmarises 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