NCEA Level 2 Earth and Space Science key terms

The theory that Earth's outer shell is broken into large rigid slabs that slowly move over the mantle, colliding, separating, or sliding past each other and causing earthquakes, volcanoes, and mountain building.

A place where two tectonic plates move towards each other. One plate may be pushed beneath the other, or the plates may crumple together, producing mountains, deep trenches, and frequent earthquakes.

A place where two tectonic plates move apart. Magma rises into the gap to form new crust, creating mid-ocean ridges under the sea or rift valleys on land, with shallow earthquakes and volcanic activity.

A place where two plates slide horizontally past each other without creating or destroying crust. Friction builds until it is released suddenly as earthquakes along faults such as the Alpine Fault.

The process in which a denser oceanic plate sinks beneath a lighter plate into the mantle. It creates deep ocean trenches, generates powerful earthquakes, and supplies water that triggers melting and volcanic arcs.

A long underwater mountain chain formed where plates pull apart and magma rises to create new oceanic crust. New rock is youngest at the ridge crest and becomes older with distance from it.

The gradual sideways growth of the ocean floor as new crust forms at mid-ocean ridges and older crust moves away. Matching magnetic stripes on either side of a ridge provide evidence for it.

The record of Earth's past magnetic field preserved in rocks. Magnetic minerals in cooling lava lock in the field direction, and the alternating stripes on the seafloor show that the field has reversed many times.

A fracture in rock where the two sides have moved relative to each other. Movement may be sudden, releasing stored energy as an earthquake, or slow and continuous, called creep.

The point on Earth's surface directly above the focus, where an earthquake began underground. It is usually the area of strongest shaking, and its distance from a seismograph is used to locate the quake.

The actual underground location where an earthquake starts and where rock first breaks and slips. Its depth helps classify an earthquake as shallow, intermediate, or deep.

An instrument that detects and records ground motion during an earthquake, producing a trace called a seismogram. The difference in arrival times of P and S waves helps find the distance to the epicentre.

A primary seismic wave that compresses and stretches rock in the direction it travels. It is the fastest seismic wave, passes through solids and liquids, and arrives first at a seismograph.

A secondary seismic wave that shakes rock sideways as it travels. It moves slower than a P wave and cannot pass through liquids, which is evidence that Earth has a liquid outer core.

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

A scale that describes the observed effects of an earthquake at a place, from barely felt to total destruction. It depends on distance, ground conditions, and building design, not just earthquake size.

The process where water-saturated loose soil loses strength and behaves like a liquid during strong shaking. Buildings may sink or tilt, and buried pipes can float upward.

A series of long ocean waves generated when a large volume of water is displaced, usually by an undersea earthquake, landslide, or volcanic eruption. Waves grow tall in shallow water near coastlines.

A curved chain of volcanoes that forms on the overriding plate above a subducting slab. Water released from the sinking plate lowers melting temperature in the mantle, producing magma that rises to the surface.

Molten rock beneath Earth's surface, containing dissolved gases and sometimes crystals. It is less dense than surrounding rock, so it rises and can feed a volcano or solidify underground as intrusive rock.

Molten rock that has reached Earth's surface through a volcanic vent. Its temperature and gas content control how runny or sticky it is, which in turn shapes the volcano's slope and eruption style.

A broad, gently sloping volcano built up by many layers of runny lava that flow far before cooling. It usually erupts quietly rather than explosively and is common at hot spots and spreading ridges.

A fixed region of unusually hot mantle that produces magma rising through a plate. As the plate moves over it, a chain of volcanoes forms, becoming older with distance from the hot spot.

The ongoing set of processes that change rock among igneous, sedimentary, and metamorphic forms through melting, cooling, weathering, erosion, burial, compaction, and heat and pressure.

Rock formed when magma or lava cools and solidifies. Slow cooling underground produces large crystals and coarse texture, while rapid cooling at the surface produces fine-grained or glassy rock.

Rock made from layers of sediment that are compacted and cemented over time, or from dissolved minerals precipitating. It commonly contains fossils and shows bedding layers and may hold groundwater.

Rock changed in the solid state by heat and pressure, usually deep underground or near magma. Its minerals recrystallise and often align in layers, producing foliation such as in schist.

The breakdown of rock in place by physical, chemical, or biological processes. Physical weathering includes freeze-thaw and root wedging; chemical weathering includes dissolution and oxidation by water and oxygen.

The transport of weathered material away from its source by agents such as water, wind, ice, or gravity. Erosion shapes landscapes and supplies the sediment that later forms sedimentary rock.

A very deep, narrow depression in the ocean floor formed where an oceanic plate bends and sinks into the mantle at a convergent boundary. Trenches mark the deepest parts of the ocean.

A scientist who proposed continental drift in the early twentieth century, arguing that continents once formed a single landmass and later moved apart. He used matching fossils, rock types, and coastlines as evidence.

The idea that continents move slowly across Earth's surface over geological time. Evidence includes matching fossils and rock layers on now-separated continents and the fit of their coastlines.

The Sun together with the objects gravitationally bound to it: eight planets, dwarf planets, moons, asteroids, comets, and dust. It formed about 4.6 billion years ago from a collapsing cloud of gas and dust.

A large body that orbits the Sun, is massive enough for gravity to make it nearly round, and has cleared other objects from its orbital path. The solar system has eight recognised planets.

A round body orbiting the Sun that has not cleared its orbital neighbourhood of other objects. Pluto, Ceres, Eris, and Makemake are examples; they share orbital regions with many smaller bodies.

A region between the orbits of Mars and Jupiter containing many rocky bodies that never combined into a planet. Its objects range from tiny fragments to hundreds of kilometres across.

A small icy body that develops a glowing coma and often a tail when it approaches the Sun and its ice vaporises. Tails point away from the Sun because of solar wind and radiation pressure.

A continuous stream of charged particles, mainly protons and electrons, flowing outward from the Sun's upper atmosphere. It shapes comet tails and can cause auroras when it interacts with Earth's magnetic field.

Coloured light in the night sky caused by charged particles from the Sun exciting gases in Earth's upper atmosphere. It is most often seen near the magnetic poles.

The region around a magnet or a body such as Earth where magnetic forces act. Earth's field, generated by motion in its liquid outer core, deflects much of the solar wind.

The liquid layer of Earth's interior between the solid inner core and the mantle, made mostly of iron and nickel. Its flowing motion generates Earth's magnetic field and it blocks S waves.

The full range of electromagnetic radiation arranged by wavelength, from radio waves through infrared, visible light, ultraviolet, X-rays, and gamma rays. Different wavelengths reveal different information about stars and planets.

The distance between two consecutive corresponding points on a wave, such as crest to crest. Shorter wavelengths carry more energy and correspond to bluer visible light.

The technique of splitting light into its component wavelengths to study it. Dark absorption lines reveal which elements are present in a star's atmosphere and how the star is moving.

The stretching of light towards longer, redder wavelengths when a source moves away from the observer. Distant galaxies show large redshifts, which is key evidence that the universe is expanding.

The model in which the universe began from an extremely hot, dense state about 13.8 billion years ago and has been expanding and cooling since. It is supported by cosmic expansion and background radiation.

Faint microwave radiation filling the universe, left over from the hot early universe. Its near-uniform temperature and tiny fluctuations are strong evidence for the Big Bang model.

The distance light travels in one year, about 9.5 trillion kilometres. Astronomers use it to express distances between stars and galaxies, not to measure time.

An enormous system of stars, gas, dust, and dark matter held together by gravity. Our Milky Way is a spiral galaxy, and billions of other galaxies exist across the observable universe.

A huge sphere of gas held together by gravity, producing light and heat through nuclear fusion in its core. Its colour and lifetime depend mainly on its mass.

The joining of light atomic nuclei into heavier ones, releasing large amounts of energy. In stars, hydrogen nuclei fuse to form helium, powering the star's light and heat.

A natural Earth process that threatens people, property, or infrastructure, such as earthquakes, volcanic eruptions, landslides, or tsunamis. Risk depends on both the hazard and how exposed and vulnerable a community is.

The chance of harm or loss from a hazard, combining the likelihood of the event with the exposure and vulnerability of what is affected. Risk can be reduced by planning, engineering, and preparedness.

A map showing where a particular hazard is likely to occur and how severe it may be. Planners use such maps to guide land use, building rules, and evacuation planning.

The systematic measurement of natural processes, such as seismic activity, ground movement, or gas emissions, to detect changes that may signal an impending hazard. Data support warnings and evacuation decisions.