NCEA Level 3 Earth and Space Science key terms

The scientific theory that Earth's rigid outer shell is broken into large plates that move slowly over the mantle, and that earthquakes, volcanoes and mountain building happen mainly at plate boundaries.

A plate margin where two plates move towards each other. Oceanic crust may be forced beneath another plate, or two continental plates may collide and crumple up to form mountains.

A plate margin where two plates move apart, allowing hot mantle rock to rise and melt. New crust forms there, producing mid-ocean ridges under oceans and rift valleys on continents.

A plate margin where two plates slide horizontally past each other. Crust is neither created nor destroyed, but stress builds and is released as shallow earthquakes along the fault.

A long, inclined region where one plate sinks beneath another into the mantle. It produces deep ocean trenches, earthquakes at increasing depths, and chains of volcanoes above the descending plate.

A raised underwater mountain chain formed where plates pull apart and magma rises to create new oceanic crust. The ridge is cut by transform faults and is the site of seafloor spreading.

The process in which new oceanic crust forms at a mid-ocean ridge and moves away from the ridge on both sides, so the ocean floor widens over time at a few centimetres per year.

Symmetrical bands of alternating normal and reversed magnetisation in oceanic crust, recording reversals of Earth's magnetic field as new crust cooled at a spreading ridge. The pattern supports seafloor spreading.

A very deep, narrow depression in the ocean floor where a subducting plate bends downward. Trenches mark convergent margins and are the deepest parts of the ocean.

A curved chain of volcanoes lying above a subducting plate, formed as water released from the sinking slab causes the overlying mantle to melt. Arcs may be on a continent or form island chains.

A fixed, unusually hot region in the mantle where melting produces volcanoes at the surface. As a plate moves over it, a chain of progressively older volcanoes forms, such as the Hawaiian Islands.

A fracture in rock along which movement has occurred. Sudden slip on a fault releases stored elastic energy as an earthquake, and the type of fault reflects the local stress direction.

Ground shaking caused by the sudden release of energy when rock breaks or slips along a fault. Energy travels outward as seismic waves and is recorded by seismographs.

The point inside the Earth where an earthquake rupture begins and seismic energy is released. Its position beneath the surface determines how far away shaking is felt.

The point on Earth's surface directly above an earthquake's focus. Shaking is usually strongest near the epicentre, though local ground conditions also affect the damage caused.

An elastic wave travelling through the Earth from an earthquake or explosion. P waves are fastest and compressional, S waves are slower and transverse, and surface waves cause much of the damage.

A logarithmic scale describing the size of an earthquake from the amplitude of seismic waves. Each whole number increase represents about 32 times more energy released.

Molten rock beneath the surface, formed when mantle or crustal rock melts. It contains dissolved gases and crystals, and its composition controls how explosively it erupts when it reaches the surface.

Molten rock that has reached Earth's surface and is flowing or has solidified. Its behaviour depends on temperature and silica content, which control how viscous and gas-rich it is.

A fluid's resistance to flow. High-silica magma is viscous and traps gas, producing explosive eruptions, while low-silica basaltic magma is runny and usually erupts gently.

The process of mountain building, usually by compression and folding of crust at a convergent plate boundary. It may involve folding, faulting, metamorphism and igneous intrusion.

Bending of layered rock under compressional stress without breaking. Upfolds are anticlines and downfolds are synclines, and the shape of folds records the direction of the forces applied.

The set of processes by which igneous, sedimentary and metamorphic rocks are formed, broken down and transformed into one another over geological time, driven by heat and by surface processes.

The breakdown of rock in place by physical, chemical or biological processes. It produces loose material and dissolved ions but does not itself transport the broken material away.

The removal and transport of weathered material by moving agents such as water, wind, ice or gravity. Erosion shapes landforms and supplies sediment to rivers, coasts and ocean basins.

The laying down of sediment when the transporting agent loses energy, for example when a river slows or a glacier melts. Deposits build up in layers that may later become sedimentary rock.

The study of layered rocks and their sequence. Because younger layers generally lie above older ones, stratigraphy lets geologists order events and correlate rock units across distances.

The total collection of preserved remains and traces of past life found in rocks. It shows that life has changed over time and provides evidence for evolution and past environments.

The process by which individuals with inherited traits that improve survival and reproduction leave more offspring, so those traits become more common in later generations of a population.

An inherited feature or behaviour that increases an organism's chance of surviving and reproducing in its particular environment. Adaptations accumulate in populations through natural selection over many generations.

A standard system dividing Earth's 4.6-billion-year history into eons, eras, periods and epochs based on major changes recorded in rocks and fossils, with boundaries dated by radiometric methods.

A method of finding the age of rocks from the ratio of a radioactive parent isotope to its stable decay product, using the known half-life. Different isotopes suit different time spans.

The time taken for half of the radioactive atoms in a sample to decay. Half-lives are constant for each isotope and allow ages to be calculated from measured isotope ratios.

The Sun and all the objects bound to it by gravity, including the eight planets, dwarf planets, moons, asteroids and comets. It formed about 4.6 billion years ago from a collapsing cloud.

The growth of larger bodies by the collision and sticking together of smaller particles and planetesimals. Accretion built the planets from dust and gas in the early solar nebula.

A small, solid body a few kilometres across that formed in the early solar nebula. Planetesimals collided and merged to build protoplanets, and some survive today as asteroids.

Three rules describing orbital motion: orbits are ellipses with the Sun at one focus; a planet sweeps equal areas in equal times; and the square of the orbital period is proportional to the cube of the semi-major axis.

The attractive force between masses, described by Newton's law and by general relativity as curvature of space-time. It keeps planets in orbit and drives accretion, tides and atmospheric layering.

The collapse of a cold, dense cloud of gas and dust under gravity until the core becomes hot and dense enough for hydrogen fusion to begin, marking the birth of a main-sequence star.

The joining of light atomic nuclei at very high temperature and pressure to form heavier nuclei, releasing large amounts of energy. Fusion of hydrogen into helium powers stars like the Sun.