MTLE Earth and Space Science (Grades 9-12) key terms

The theory that Earth's rigid outer shell is broken into large slabs that move over the softer mantle, causing earthquakes, volcanoes, mountain building, and the formation of ocean basins at their boundaries.

A place 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.

A place where two plates move toward each other, producing subduction, deep ocean trenches, volcanic arcs, or continental collision and high mountain ranges depending on the crust types involved.

A boundary where two plates slide horizontally past one another, generating shallow-focus earthquakes along strike-slip faults without significant volcanic activity or crust creation.

A convergent setting where denser oceanic lithosphere descends beneath another plate into the mantle, producing trenches, earthquakes, and chains of volcanoes above the sinking slab.

The process by which new oceanic crust forms at mid-ocean ridges as magma rises and solidifies, then moves away symmetrically, recording reversals of Earth's magnetic field in striped patterns.

The record of Earth's past magnetic field direction and strength preserved in magnetic minerals of rocks; seafloor magnetic stripes and apparent polar wandering support plate motion and field reversals.

A swap of Earth's magnetic polarity in which north and south magnetic poles exchange positions; these flips are recorded in cooling lava and seafloor crust and help date geologic events.

A curved chain of volcanic islands formed above a subducting oceanic plate, typically separated from the continent by a back-arc basin; common around the Pacific margin.

A long-lived zone of upwelling mantle heat that produces volcanism at a fixed location; as a plate moves over it, a chain of progressively older volcanoes forms.

A fracture in rock along which movement has occurred; classified as normal, reverse, or strike-slip according to the direction of slip and the stress that produced it.

The point on Earth's surface directly above the focus of an earthquake, usually the location of strongest shaking and the reference point used to report an earthquake's position.

The actual subsurface point where an earthquake rupture begins and seismic energy is released; its depth determines whether an earthquake is shallow, intermediate, or deep.

Elastic energy traveling through Earth after a rupture; P waves compress and stretch rock, S waves shear it, and surface waves travel along the surface and typically cause the most damage.

A logarithmic scale measuring earthquake size from the total energy released, based on rupture area, slip amount, and rock rigidity; it supersedes older Richter magnitude for large quakes.

Magma rich in magnesium and iron and relatively low in silica; it is fluid, allows gases to escape easily, and typically produces gentle lava flows and shield volcanoes.

Magma high in silica and lower in iron and magnesium; it is viscous, traps gases, and commonly erupts explosively, forming steep composite cones and rhyolitic domes.

A steep, layered cone built from alternating lava flows and explosive ash deposits, typical of subduction zones where viscous, gas-rich magma produces violent eruptions.

A broad, gently sloping volcano formed by repeated fluid lava flows; typical of hot spots and spreading centers where low-viscosity mafic magma erupts quietly.

A belt of volcanoes parallel to a subduction zone, formed where fluids released from the descending slab trigger melting in the overlying mantle wedge.

The in-place breakdown of rock by physical processes such as freeze-thaw and abrasion or by chemical reactions such as hydrolysis and oxidation, without transporting the material away.

The removal and transport of weathered material by agents such as flowing water, wind, ice, and gravity; it shapes landforms and supplies sediment to depositional basins.

Loose fragments of rock, mineral grains, or organic remains that have been weathered, transported, and deposited; when buried and cemented, sediment becomes sedimentary rock.

The set of processes, chiefly compaction and cementation, that convert loose sediment into solid sedimentary rock after deposition and burial.

Rock formed from compacted and cemented sediment or from chemical precipitation and organic accumulation; its layers preserve clues about past environments and often contain fossils.

Rock changed in the solid state by heat, pressure, or chemically active fluids, often developing foliation or new minerals that indicate the conditions of metamorphism.

A planar layering in metamorphic rock produced by aligned platy minerals or compositional banding under directed pressure, giving rocks such as slate and gneiss their distinctive fabric.

The set of processes by which igneous, sedimentary, and metamorphic rocks transform into one another through melting, cooling, weathering, deposition, burial, and metamorphism.

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.

A fossil of a species that lived over a short time span but had a wide geographic range, making it useful for correlating rock layers and determining relative ages.

A method of determining absolute age by measuring the ratio of a radioactive parent isotope to its decay product in a sample and applying the known half-life.

The time required for half of the radioactive atoms in a sample to decay; each isotope has a characteristic value, allowing decay ratios to serve as a geologic clock.

A surface in rock strata representing a gap in the geologic record, produced by erosion or a pause in deposition and often marked by missing layers or buried erosion surfaces.

Warming of a planet's surface as atmospheric gases absorb and re-radiate outgoing infrared radiation; it keeps Earth habitable but intensifies with added greenhouse gases.

The fraction of incoming solar radiation reflected back to space by a surface or planet; bright ice and clouds have high albedo, while dark oceans and land have low albedo.

The amount of solar radiation reaching a given area of Earth's surface; it varies with latitude, season, and angle of incidence and drives atmospheric and oceanic circulation.

The apparent deflection of moving air and water caused by Earth's rotation, to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.

A persistent, directed flow of seawater driven by wind, differences in density from temperature and salinity, tides, and Earth's rotation; currents redistribute heat globally.

The slow, global overturning of the ocean driven by differences in temperature and salinity that create density contrasts, linking surface and deep water and moving heat and nutrients.

The exchange of carbon among the atmosphere, oceans, land, and living things through photosynthesis, respiration, decay, combustion, and dissolution; it regulates atmospheric carbon dioxide.

The relationship stating that the square of a planet's orbital period is proportional to the cube of its semi-major axis, allowing orbital period to predict distance from the Sun.

The principle that each planet orbits the Sun along an ellipse with the Sun at one focus, so the planet-Sun distance changes over the course of a revolution.

A number describing how much an orbit or ellipse departs from a circle; zero is circular, values between zero and one are elliptical, and higher values mean more elongated orbits.

The time a body takes to complete one revolution around another body; for planets it increases with distance from the Sun according to Kepler's third law.

A continuous stream of charged particles flowing outward from the Sun's corona; it shapes planetary magnetospheres and produces auroras and comet tails.

An approximately eleven-year variation in the number and latitude of dark magnetic regions on the Sun, linked to the Sun's magnetic field reversal and space weather.

The model that the Solar System formed from a rotating cloud of gas and dust that collapsed, flattened into a disk, and accreted into the Sun and planets.

The growth of larger bodies by the collision and sticking together of smaller particles and planetesimals in the early solar nebula.

A small, solid body, roughly kilometers across, formed in the solar nebula and serving as a building block of planets through continued collisions and accretion.

A small, dense, rocky planet with a solid surface and thin atmosphere, characteristic of Mercury, Venus, Earth, and Mars because they formed close to the Sun.

A large, low-density planet of hydrogen, helium, and ices, with strong gravity and many moons; Jupiter, Saturn, Uranus, and Neptune formed beyond the frost line.

The formation of chemical elements through nuclear fusion inside stars, which builds heavier nuclei from lighter ones and releases energy; supernovae disperse these elements.

The long phase of a star's life when it fuses hydrogen into helium in its core and shines steadily; its position on an H-R diagram depends mainly on mass.

A graph of stellar luminosity versus temperature or spectral class that reveals the main sequence, giants, and white dwarfs, and helps explain stellar evolution.

The explosive death of a massive star or an accreting white dwarf, which briefly outshines a galaxy and disperses newly formed heavy elements into space.

The shift of spectral lines toward longer wavelengths when a source moves away; for galaxies it indicates recession and supports an expanding universe.

The observation that a galaxy's recession speed is proportional to its distance, implying that the universe is expanding uniformly in all directions.

The prevailing model that the universe expanded from an extremely hot, dense state roughly 13.8 billion years ago, supported by expansion, the microwave background, and light-element abundances.

The cooled afterglow of the early universe, observable as nearly uniform microwave radiation in every direction, with faint temperature ripples marking density variations.