ILTS Earth and Space Science (241) key terms

The state of gravitational balance in which lighter crustal blocks float at an elevation supported by denser mantle rock beneath them; loading or unloading the crust causes vertical adjustment until balance is restored.

The unifying theory that Earth's rigid lithosphere is broken into plates that move over the weaker asthenosphere, driven by mantle convection and slab pull, producing earthquakes, volcanoes, and mountain belts at their boundaries.

A boundary where two lithospheric plates move apart, allowing magma to rise and form new crust; expressed as mid-ocean ridges under oceans and rift valleys on continents, with shallow earthquakes and basaltic volcanism.

A boundary where plates move toward each other, producing subduction zones with deep earthquakes and arc volcanoes, or continental collision zones with fold-and-thrust mountain belts; oceanic lithosphere is destroyed here.

A boundary where two plates slide horizontally past one another without creating or destroying crust, generating shallow strike-slip earthquakes along faults such as the San Andreas fault system.

A convergent setting where one plate descends beneath another into the mantle, marked by a deep ocean trench, a dipping seismic zone, and a volcanic arc; the descending slab also drives plate motion through slab pull.

The process by which new oceanic crust forms at mid-ocean ridges as magma rises and solidifies, then moves away symmetrically on both sides; magnetic stripe patterns and age dates record the spreading history.

The record of ancient magnetic field direction and polarity preserved in magnetic minerals of rocks; alternating polarity stripes in oceanic crust and apparent polar wander provided key evidence for continental drift and seafloor spreading.

Wegener's early twentieth-century hypothesis that continents once formed a single landmass and later moved apart; supported by matching coastlines, fossils, rock units, and glacial deposits across ocean basins, though lacking a viable mechanism.

The explanation of earthquakes in which rock bends elastically as stress accumulates along a locked fault, then ruptures and snaps back to an unstrained shape, releasing stored energy as seismic waves.

Energy transmitted through Earth as vibrations; P waves are compressional and travel through solids and fluids, S waves are shear waves that cannot pass through liquids, and surface waves cause the strongest shaking.

The boundary separating Earth's crust from the underlying mantle, detected by an abrupt increase in seismic wave velocity; it lies about 5-10 km beneath ocean floors and 30-50 km beneath continents.

The order in which silicate minerals crystallize from cooling magma: olivine and calcium-rich plagioclase first at high temperature, then pyroxene, amphibole, biotite, and finally quartz and potassium feldspar at low temperature.

Rock formed by cooling and solidification of magma or lava; intrusive types such as granite cool slowly and have coarse crystals, while extrusive types such as basalt cool quickly and are fine-grained or glassy.

The process by which a single parent magma produces compositionally varied rocks, chiefly through fractional crystallization as early-formed minerals are removed, plus assimilation of wall rock and mixing of magmas.

The solid-state recrystallization of rock in response to changed temperature, pressure, or fluid conditions, producing foliated rocks such as schist and gneiss or nonfoliated rocks such as marble and quartzite without melting.

The set of processes that continually transform Earth materials among igneous, sedimentary, and metamorphic rocks through melting, crystallization, weathering, erosion, deposition, burial, and metamorphism.

The in-place breakdown of rock by physical processes such as frost wedging and abrasion or by chemical processes such as hydrolysis and oxidation; it produces regolith and soil but does not itself transport material.

The removal and transport of weathered material by moving agents such as water, wind, ice, and gravity; erosion shapes landforms and is distinct from weathering, which only breaks material down in place.

The laying down of sediment when a transporting medium loses energy, for example where a river slows at its mouth or a glacier melts; deposited layers may later lithify into sedimentary rock.

Rock formed from compacted and cemented sediment or from chemical precipitation; clastic types such as sandstone preserve grain size and sorting, while limestone and evaporites record chemical conditions of deposition.

The principle that in an undisturbed sequence of layered sedimentary rocks, each layer is older than the one above it and younger than the one below, providing the basis for relative dating.

A fossil used to correlate rock layers across regions because its species was widespread, abundant, and short-lived in geologic time; its presence narrows the age of the enclosing strata.

Determining absolute rock ages by measuring the ratio of a radioactive parent isotope to its stable daughter product and applying the known half-life; useful isotopes include carbon-14, potassium-40, and uranium-238.

The time required for half of the radioactive atoms in a sample to decay; after two half-lives one quarter of the original parent atoms remain, and the ratio allows calculation of sample age.

A surface in the rock record representing a gap in time caused by erosion or nondeposition; angular unconformities, disconformities, and nonconformities each reveal a different sequence of events.

A geologically rapid loss of a large share of species, documented in the fossil record; the end-Permian and end-Cretaceous events are the largest, the latter linked to an asteroid impact and flood volcanism.

The global deep-ocean conveyor driven by differences in water temperature and salinity, which control density; cold, salty water sinks in high latitudes and slowly returns elsewhere, redistributing heat and nutrients.

The apparent deflection of moving objects on a rotating planet, to the right in the Northern Hemisphere and left in the Southern; it steers winds and ocean currents but does not cause them.

The rise of cold, nutrient-rich water from depth to the surface, often caused by offshore winds and Ekman transport; upwelling zones support highly productive fisheries along western continental margins.

The periodic rise and fall of sea level caused mainly by the gravitational pull of the Moon and Sun; spring tides occur at new and full moons, neap tides at quarter moons, and coastal shape modifies the range.

The rate at which a rising or sinking air parcel changes temperature through expansion or compression without exchanging heat with surroundings; the dry rate is about 10 degrees Celsius per kilometer, the saturated rate smaller.

The change of water vapor into liquid droplets or ice crystals, occurring when air cools to its dew point; it releases latent heat and forms clouds, fog, and precipitation nuclei.

A large body of air with relatively uniform temperature and humidity acquired over a source region; classified as continental or maritime and polar, tropical, or arctic, it brings characteristic weather when it moves.

The boundary between two air masses of different density; a cold front brings steep uplift and short intense storms, a warm front brings gentle widespread precipitation, and a stationary or occluded front stalls or lifts.

Three descriptions of orbital motion: planets follow ellipses with the Sun at one focus, sweep equal areas in equal times, and have orbital periods squared proportional to semimajor axes cubed.

The nebular model in which a collapsing cloud of gas and dust flattened into a disk, forming the Sun at the center and accreting planets from planetesimals; inner planets are rocky, outer planets icy and gaseous.

The shift in observed wavelength caused by relative motion between source and observer; redshift of galaxy spectra indicates recession and underlies Hubble's law and the expanding-universe interpretation.

The systematic process of asking testable questions, forming hypotheses, gathering evidence through observation or controlled experiment, analyzing data, and revising explanations; conclusions are always provisional and open to replication.

Evaluating a proposed explanation by deriving predictions and comparing them with evidence; a hypothesis must be falsifiable, and results either support it, refute it, or call for revised methods and further investigation.

Ongoing, low-stakes gathering of evidence about student understanding during instruction, used to adjust teaching in real time; examples include questioning, exit tickets, and concept inventories in Earth science.