Earth Science Lecture Notes Review

Flashcards of key vocabulary terms and definitions from Earth Science lecture notes.

Asthenosphere

The layer of the mantle that lies between 100–150 km and 350 km deep; the asthenosphere is relatively soft and can flow when acted on by force

Bathymetry

Variation in depth.

Crust

Outermost, solid layer of our planet, composed of rock, and is thinner than the layers beneath. It's divided into two main types: oceanic crust and continental crust.

Dipole

A magnetic field with a north and south pole, like that of a bar magnet

Isostasy

The condition that exists when the buoyancy force pushing lithosphere up equals the gravitational force pulling lithosphere down

Geothermal gradient

The rate of change in temperature with depth.

Lithosphere

The relatively rigid, nonflowable, outer 100- to 150-km-thick layer of the Earth, constituting the crust and the top part of the mantle.

Moho

The seismic-velocity discontinuity that defines the boundary between the Earth’s crust and mantle. Named for Andrija Mohorovičić.

Nebula

A cloud of gas or dust in space.

Igneous

Forms when hot molten rock (magma or lava) cools and freezes solid.

Silicate rock

Most of the rock in the geosphere, most common on earth

Accretionary prism

A wedge-shaped mass of sediment and rock scraped off the top of a downgoing plate and accreted onto the overriding plate at a convergent plate margin.

Active margin

A continental margin that is also a plate boundary

Apparent polar-wander path

A path on the globe along which a magnetic pole appears to have wandered over time; in fact, the continents drift, while the magnetic pole stays fairly-fixed.

Continental rift

A linear belt along which continental lithosphere stretches and pulls apart.

Convergent boundary

A boundary at which two plates move toward each other so that one plate sinks (subducts) beneath the other; only oceanic lithosphere can subduct

Divergent boundary

A boundary at which two lithosphere plates move apart from each other; they are marked by mid-ocean ridges.

Fracture zone

A narrow band of vertical fractures in the ocean floor; fracture zones lie roughly at right angles to a mid-ocean ridge, and the actively slipping part of a fracture zone is a transform fault.

Hot spot

A location at the base of the lithosphere, at the top of a mantle plume, where temperatures can cause melting.

Magnetic anomaly

The difference between the expected strength of the Earth’s magnetic field at a certain location and the actual measured strength of the field at that location.

Magnetic reversal

Earth’s magnetic field itself flips every now and then, and quickly

Mantle plume

A column of very hot rock that rises up through the mantle

Mid-ocean ridge

A 2-km-high submarine mountain belt that forms along a divergent oceanic plate boundary.

Passive margin

A continental margin that does not coincide with a plate boundary, and therefore does not display seismicity.

Plate

One of about 20 distinct pieces of the relatively rigid lithosphere

Plate boundary

The border between two adjacent lithosphere plates.

Rift

The process by which continental lithosphere stretches horizontally and thins vertically

Seafloor spreading

The gradual widening of an ocean basin as new oceanic crust forms at a mid-ocean ridge axis and then moves away from the axis.

Subduction

The process by which one oceanic plate bends and sinks down into the asthenosphere beneath another plate

Transform boundary

A boundary at which two plates slide sideways past each other

Trench

A deep, elongate trough bordering a volcanic arc; a trench defines the trace of a convergent plate boundary

Triple Junction

A point where three lithosphere plate boundaries intersect.

Volcanic arc

A curving chain of active volcanoes formed adjacent to a convergent plate boundary

Crystal

A single, continuous piece of a mineral bounded by flat surfaces that formed naturally as the mineral grew

Crystal habit

The general shape of a crystal or cluster of crystals that grew unimpeded.

Crystal lattice

Three dimensional geometry of points representing alternation of atoms

Glass

A solid in which atoms are not arranged in an orderly pattern.

Mineral

A homogenous, naturally occurring, solid inorganic substance with a definable chemical composition and an internal structure characterized by an orderly arrangement of atoms, ions, or molecules in a lattice. Most minerals are inorganic.

Polymorph

Two minerals that have the same chemical composition but a different crystal lattice structure.

Assimilation

The process of magma contamination in which blocks of wall rock fall into a magma chamber and dissolve.

Batholith

A vast composite, intrusive, igneous rock body up to several hundred km long and 100 km wide, formed by the intrusion of numerous plutons in the same region

Dike

A tabular (wall-shaped) intrusion of rock that cuts across the layering of country rock

Flood basalt

Vast sheets of basalt that spread from a volcanic vent over an extensive surface of land; they may form where a rift develops above a continental hot spot, and where lava is particularly hot and has low viscosity.

Magma

Molten rock beneath the Earth’s surface

Lava

Molten rock that has flowed out onto the Earth’s surface

Pluton

An irregular or blob-shaped intrusion; can range in size from tens of m across to tens of km across

Sill

A nearly horizontal tabletop-shaped tabular intrusion that occurs between the layers of country rock.

Vesicle

Open holes in igneous rock formed by the preservation of bubbles in magma as the magma cools into solid rock.

Xenolith

A relict of wall rock surrounded by intrusive rock when the intrusive rock freezes

Active volcano

A volcano that has erupted within the past few centuries and will likely erupt again

Ash

Tiny glass shards formed when a fine spray of exploded lava freezes instantly upon contact with the atmosphere.

Caldera

A large circular depression with steep walls and a fairly-flat floor, formed after an eruption as the center of the volcano collapses into the drained magma chamber below.

Columnar jointing

A type of fracturing that yields roughly hexagonal columns of basalt; columnar joints form when a dike, sill, or lava flow cools.

Crater

(1) A circular depression at the top of a volcanic mound; (2) a depression formed by the impact of a meteorite.

Dormant volcano

A volcano that has not erupted for hundreds to thousands of years but does have the potential to erupt again in the future.

Extinct volcano

A volcano that was active in the past but has now shut off entirely and will not erupt in the future.

Large Igneous Province

A region in which huge volumes of lava and/or ash erupted over a relatively short interval of geologic time.

Pyroclastic flow

A fast-moving avalanche that occurs when hot volcanic ash and debris mix with air and flow down the side of a volcano.

Shield volcano

A subaerial volcano with a broad, gentle dome, formed either from low-viscosity basaltic lava or from large pyroclastic sheets.

Stratovolcano

A large, cone-shaped subaerial volcano consisting of alternating layers of lava and tephra

Supervolcano

A volcano that erupts a vast amount (more than 1,000 cubic km) of volcanic material during a single event; none have erupted during recorded human history.

Chemical weathering

The process in which chemical reactions alter or destroy minerals when rock comes in contact with water solutions and/or air

Clast

A fragment or grain produced by the physical or chemical weathering of a pre-existing rock.

Physical weathering

The process in which intact rock breaks into smaller grains or chunks.

Sediment

An accumulation of loose mineral grains, such as boulders, pebbles, sand, silt, or mud, that are not cemented together.

Soil

Sediment that has undergone changes at the surface of the Earth, including reaction with rainwater and the addition of organic material.

Alluvial fan

A gently sloping apron of sediment dropped by an ephemeral stream at the base of a mountain in arid or semiarid regions.

Chemical sedimentary rock

Sedimentary rocks made up of minerals that precipitate directly from water solution

Cementation

The phase of lithification in which cement, consisting of minerals that precipitate from groundwater, partially or completely fills the spaces between clasts and attaches each grain to its neighbor.

Clastic sedimentary rock

Sedimentary rock consisting of cemented-together detritus derived from the weathering of preexisting rock.

Coal

A black, organic rock consisting of greater than 50% carbon; it forms from the buried and altered remains of plant material.

Conglomerate

Very coarse-grained sedimentary rock consisting of rounded clasts.

Diagenesis

All of the physical, chemical, and biological processes that transform sediment into sedimentary rock and that alter the rock after the rock has formed.

Evaporite

Thick salt deposits that form as a consequence of precipitation from saline water

Facies

A set of metamorphic mineral assemblages indicative of metamorphism under a specific range of pressures and temperatures.

Fossil

The remnant, or trace, of an ancient living organism that has been preserved in rock or sediment.

Lithification

The transformation of loose sediment into solid rock through compaction and cementation.

Mudstone

Very fine-grained sedimentary rock that will not easily split into sheets

Shale

Very fine-grained sedimentary rock that breaks into thin sheets.

Regression

The seaward migration of a shoreline caused by a lowering of sea level.

Sandstone

Coarse-grained sedimentary rock consisting almost entirely of quartz

Strata

A succession of several layers or beds together.

Transgression

The inland migration of shoreline resulting from a rise in sea level.

Turbidity current/turbidite

A submarine avalanche of sediment and water that speeds down a submarine slope

Aftershock

The series of smaller earthquakes that follow a major earthquake

Body wave

Seismic waves that travel along the Earth’s surface

Compressional wave

Waves in which particles of material move back and forth parallel to the direction in which the wave itself moves.

Displacement

The amount of movement or slip across a fault plane.

Epicenter

The point on the surface of the Earth directly above the focus of an earthquake.

Fault

A fracture on which one body of rock slides past another.

Focus

The location where a fault slips during an earthquake (hypocenter)

Magnitude

A representation of the energy released by an earthquake, as indicated by the amplitude of specific seismic waves as they would be recorded by a seismometer at a set distance from the epicenter.

Richter scale

A scale that defines earthquakes on the basis of the amplitude of the largest ground motion recorded on a seismogram

Shear wave

Seismic waves in which particles of material move back and forth perpendicular to the direction in which the wave itself moves.

Stick-slip behavior

Stop-start movement along a fault plane caused by friction, which prevents movement until stress builds up sufficiently.

Surface wave

Seismic waves that travel along the Earth’s surface.

Tsunami

A large wave along the sea surface triggered by an earthquake or large submarine slump.

Anticline

A fold with an arch-like shape in which the limbs dip away from the hinge.

Basin

A depression, created as a consequence of subsidence, that fills with sediment.

Brittle deformation

The cracking and fracturing of a material subjected to stress.