WACE ATAR Earth & Environmental Science key terms

The theory that Earth's rigid outer shell is broken into large slabs that drift over the softer mantle, colliding, separating or sliding past one another and generating most earthquakes, volcanoes and mountain belts.

The cool, rigid outer layer of Earth comprising the crust and uppermost mantle, broken into tectonic plates that move over the weaker asthenosphere beneath them.

The hot, partially molten and ductile layer of the upper mantle beneath the lithosphere. It flows slowly over geological time, allowing tectonic plates to move across its surface.

A convergent boundary where one denser plate sinks beneath another into the mantle. It produces deep ocean trenches, volcanic arcs, and powerful earthquakes along the descending slab.

A boundary where two plates move apart and new crust forms from upwelling magma. It creates mid-ocean ridges on the seafloor and rift valleys within continents.

A boundary where two plates move towards each other. Depending on the crust involved, it produces subduction zones with volcanic arcs, or continental collision forming fold mountain belts.

A boundary where two plates slide horizontally past each other without creating or destroying crust. Friction is released as shallow earthquakes along the fault line.

The process at mid-ocean ridges where magma rises, solidifies and pushes older oceanic crust sideways. Magnetic stripes and increasing sediment thickness away from ridges record this motion.

The record of Earth's past magnetic field preserved in cooling rocks. Reversals captured as symmetrical stripes on the seafloor provided key evidence for seafloor spreading and plate tectonics.

A naturally occurring, inorganic solid with a definite chemical composition and an ordered internal atomic structure, giving characteristic properties such as hardness, cleavage and crystal form.

A naturally occurring aggregate of one or more minerals, or of mineral-like material such as volcanic glass. Rocks are classified as igneous, sedimentary or metamorphic by origin.

Rock formed when molten material cools and solidifies. Slow cooling underground produces coarse-grained intrusive rock, while rapid cooling at the surface produces fine-grained or glassy extrusive rock.

Rock formed from compacted and cemented sediment, or from chemical precipitation, or from accumulated organic remains. Layers called strata preserve evidence of past environments and often contain fossils.

Rock altered in the solid state by heat, pressure or chemically active fluids, typically deep underground. New minerals and foliation develop without the rock melting.

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

A relative ranking from one (talc) to ten (diamond) of how easily minerals are scratched. It is a simple field test for identifying unknown mineral specimens.

A mineral built around silicon-oxygen tetrahedra, the most abundant mineral group in Earth's crust. Silicate structure controls properties such as cleavage, melting temperature and magma viscosity.

The breakdown of rocks and minerals in place by physical, chemical or biological processes. It produces sediment and dissolved ions that are then removed by erosion.

The removal and transport of weathered material by agents such as water, wind, ice and gravity. It shapes landforms and delivers sediment to depositional basins.

The laying down of transported sediment when the carrying agent loses energy, for example where a river slows or a glacier melts. Deposits build up in layers over time.

A fracture in rock along which movement has occurred. Sudden slip on faults releases stored elastic strain as earthquakes, while slow creep may occur without noticeable shaking.

A mountain range formed where compressional forces buckle layered rock into anticlines and synclines, often during continental collision. The Himalayas are a modern example.

The study of rock layers and their sequence. Principles such as superposition and cross-cutting relationships allow relative ages of rocks and events to be determined.

The standard division of Earth's 4.6-billion-year history into eons, eras, periods and epochs, based on major changes in rocks and fossils and calibrated with radiometric dates.

The spontaneous transformation of unstable isotopes into daughter products at a fixed rate. Measuring parent-to-daughter ratios in minerals gives absolute ages for rocks and events.

The time required for half the atoms of a radioactive isotope in a sample to decay. Different isotopes have very different half-lives, making them suitable for dating materials of different ages.

Preserved evidence of past life, such as mineralised bones, shells, impressions or trace marks in rock. Fossils indicate relative ages and reconstruct past environments and climates.

The point on Earth's surface directly above the focus of an earthquake. It usually experiences the strongest shaking, with intensity decreasing outwards from it.

An energy wave generated by an earthquake or explosion and transmitted through Earth. P-waves and S-waves travel at different speeds and reveal the planet's internal structure.

The layer of gases held around Earth by gravity, mainly nitrogen and oxygen with trace greenhouse gases. It regulates temperature, weather and climate and shields the surface from radiation.

The warming of a planet's surface because certain atmospheric gases absorb and re-emit outgoing infrared radiation. Human emissions have strengthened it, driving global warming.

The fraction of incoming solar radiation reflected by a surface. Ice and snow have high albedo, while oceans and forests are dark and absorb more energy, influencing climate feedbacks.

The apparent deflection of moving air or water caused by Earth's rotation. It turns winds and currents to the right in the northern hemisphere and to the left in the southern hemisphere.

A large-scale, persistent flow of seawater driven by wind, temperature and salinity differences and Earth's rotation. Currents redistribute heat and strongly influence regional climate.

The slow global overturning of the ocean driven by differences in temperature and salinity, which control seawater density. It transports heat, nutrients and dissolved gases between ocean basins.

The rise of cold, nutrient-rich water from depth to the surface, typically caused by winds moving surface water offshore. It supports highly productive fisheries and influences coastal climate.

A body of rock or sediment that stores and transmits groundwater in usable quantities. Its porosity and permeability determine yield, and over-extraction can cause subsidence or salinisation.

Water held in pores and fractures beneath the ground surface. It supplies drinking water and sustains streams and ecosystems, but recharges slowly and can be polluted or over-used.

The upper surface of the saturated zone in an aquifer, below which all pores are filled with water. It rises and falls with rainfall, pumping and seasonal demand.

The exchange of carbon among the atmosphere, oceans, living organisms, soils and rocks. Photosynthesis, respiration, combustion and weathering move carbon between reservoirs over varied timescales.

The pathways by which nitrogen moves between the atmosphere, organisms and soil. Fixation, nitrification, assimilation and denitrification, all largely microbial, make nitrogen available to life.

Nutrient enrichment of a water body, usually by nitrogen and phosphorus, causing algal blooms and later oxygen depletion. It degrades water quality and can kill fish and other aquatic life.

A vertical section through soil showing distinct horizons from surface litter down to weathered parent material. Horizon development reflects climate, vegetation, slope and time.

The relative proportions of sand, silt and clay particles in a soil. Texture controls water retention, drainage, aeration and fertility, and is often shown on a triangular classification diagram.

The ability of a rock or soil to allow fluids to pass through its connected pore spaces. High permeability aids drainage and groundwater flow but can also allow pollutants to spread quickly.

The variety of genes, species and ecosystems in a given area. It underpins ecosystem resilience and services, and is reduced by habitat loss, pollution, over-exploitation and climate change.

A benefit people obtain from ecosystems, such as food, clean water, pollination, carbon storage and recreation. These services are often invisible until degraded.

Meeting present needs without compromising the ability of future generations to meet theirs. It balances environmental, social and economic considerations in resource use and development decisions.

A natural resource replenished by natural processes at a rate comparable to or faster than human use, such as sunlight, wind, timber or fish stocks. Over-use can still deplete some renewable resources.

A process in which a change amplifies itself, pushing a system further in the same direction. Melting ice lowering albedo, which increases warming, is a well-known example.

Past climates reconstructed from proxies such as ice cores, tree rings, sediments and fossils. These records show natural variability and help place current warming in context.