HSC Earth and Environmental Science key terms

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

The process where a denser tectonic plate sinks beneath another plate into the mantle. It generates deep ocean trenches, volcanic arcs and powerful earthquakes along the descending slab.

A plate margin where two plates move apart, allowing magma to rise and form new crust. Examples include mid-ocean ridges, where sea-floor spreading creates new oceanic lithosphere.

A plate margin where two plates move towards each other. Depending on crust type, this produces subduction zones, volcanic arcs, trenches or collisional mountain belts.

The creation of new oceanic crust at mid-ocean ridges as magma rises, cools and moves away from the ridge, carrying older crust outward and recording magnetic reversals in stripes.

A long underwater mountain chain formed where plates diverge and magma upwells. Ridges are sites of new crust formation, shallow earthquakes and hydrothermal vent communities.

A deep, narrow depression in the ocean floor formed where one plate subducts beneath another. Trenches mark the deepest parts of the ocean and border volcanic island arcs.

The record of Earth's past magnetic field preserved in rocks. Magnetic stripes on the sea floor and apparent polar wander provide evidence for sea-floor spreading and continental drift.

The historical hypothesis that continents have moved across Earth's surface over geological time, supported by matching coastlines, fossils, rock sequences and glacial deposits on now-separated landmasses.

The process of mountain building caused by compression and deformation of the crust, usually at convergent plate margins, producing folding, faulting, metamorphism and uplifted ranges.

The breakdown of rocks in place by physical, chemical or biological processes. Weathering produces sediment and soil without transporting material away from the original site.

The removal and transport of weathered rock, sediment or soil by agents such as water, wind, ice and gravity. Erosion shapes landforms and can degrade land when vegetation is removed.

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

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

The change of existing rock by heat, pressure or chemically active fluids without melting. Metamorphic rocks develop new minerals and textures that record the conditions they experienced.

The set of processes that continually transform rock among igneous, sedimentary and metamorphic types through melting, cooling, weathering, erosion, deposition and metamorphism over geological time.

A naturally occurring concentration of minerals that can be extracted economically. Whether a deposit is a resource depends on grade, accessibility, technology, price and environmental constraints.

A body of rock containing minerals in concentrations high enough to be mined profitably. Ore deposits form through processes such as magmatic segregation, hydrothermal activity and sedimentary concentration.

Preserved remains or traces of past life, usually found in sedimentary rock. Fossils provide evidence of evolution, past environments and the relative ages of rock layers.

Layers of sedimentary rock stacked over time. Because younger layers generally lie above older ones, strata allow relative dating and interpretation of past depositional environments.

The layer of gases held around Earth by gravity. It supplies oxygen and carbon dioxide, moderates temperature, shields the surface from radiation and drives weather and climate.

The warming of Earth's surface as certain atmospheric gases absorb and re-emit outgoing infrared radiation. The natural effect keeps Earth habitable; human emissions have strengthened it.

A gas such as carbon dioxide, methane, nitrous oxide or water vapour that absorbs infrared radiation and warms the atmosphere. Concentrations of several have risen due to human activity.

The additional warming caused when human activities increase greenhouse gas concentrations above natural levels, altering global temperature, rainfall patterns and sea level.

The proportion of incoming solar radiation reflected by a surface. Ice and snow have high albedo while oceans and dark land have low albedo, so albedo changes can amplify or dampen warming.

The lowest layer of the atmosphere, where most weather occurs and temperature generally falls with height. It contains most atmospheric water vapour and is well mixed by convection.

The movement of carbon between the atmosphere, oceans, soils, living organisms and rocks through processes such as photosynthesis, respiration, decomposition, combustion and dissolution.

The continuous movement of water through evaporation, transpiration, condensation, precipitation, runoff and infiltration, linking oceans, atmosphere, land and living things.

The downward movement of water from the surface into soil and rock. Infiltration rates depend on soil texture, vegetation, slope and moisture, and influence groundwater recharge and runoff.

A permeable rock or sediment layer that stores and transmits groundwater in usable quantities. Aquifers can be recharged slowly and may be depleted by over-extraction or pollution.

The area of land drained by a river and its tributaries, bounded by ridges and divides. Catchment characteristics such as land use, soil and vegetation affect water quality and flow.

A community of living organisms interacting with each other and their physical environment, linked by flows of energy and cycling of matter. Ecosystems vary in scale from a pond to a forest.

The variety of living things, including genetic diversity within species, diversity of species and diversity of ecosystems. High biodiversity generally increases ecosystem resilience to disturbance.

A feeding position in a food chain, such as producer, primary consumer or predator. Energy is lost at each transfer, so higher trophic levels support fewer organisms and less biomass.

A network of interconnected food chains showing which organisms eat which in an ecosystem. Food webs illustrate energy flow and the indirect effects of removing or adding species.

The process by which plants, algae and some bacteria use sunlight to convert carbon dioxide and water into glucose and oxygen, forming the base of most food webs and removing carbon from the atmosphere.

The release of energy from organic molecules by living cells, typically using oxygen and producing carbon dioxide and water. Respiration returns carbon to the atmosphere and supports metabolism.

The maximum population size an environment can sustain indefinitely given available resources such as food, water and space. Exceeding it leads to resource depletion and population decline.

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.

A formal process that predicts the likely environmental effects of a proposed project and identifies ways to avoid, reduce or manage them before approval is granted.

Actions taken to reduce the severity or likelihood of an environmental impact, such as designing lower-emission technology, restoring habitat or changing management practices.

The enrichment of water with nutrients, often from fertiliser or sewage, causing algal blooms that deplete oxygen when they decay and can kill aquatic animals.

A process in which a change triggers further changes that either amplify the original change, called positive feedback, or reduce it, called negative feedback. Feedback affects system stability.

A set of interacting components that exchange energy and matter and behave as a whole. Earth can be studied as interacting systems: geosphere, atmosphere, hydrosphere and biosphere.

The capacity of a system or ecosystem to absorb disturbance and recover its structure and function. Resilience is supported by biodiversity, connectivity and diverse response options.

A testable, specific statement proposing an explanation for an observation. A hypothesis must be able to be supported or rejected by evidence collected through investigation.

A factor that can change in an investigation. Independent variables are manipulated, dependent variables are measured, and controlled variables are kept constant to ensure fair comparison.

The extent to which repeated measurements give consistent results. Reliability is improved by repeated trials, larger samples and careful standardisation of measurement procedures.

The extent to which an investigation measures what it claims to measure and the conclusions are justified. Validity depends on appropriate design, controls and accurate measurement.

A line or strip across a study area along which samples or observations are recorded. Transects are used in fieldwork to detect patterns such as changes across a habitat boundary.

A defined sample area, often a square frame, placed in a habitat to count or estimate organisms. Quadrats allow representative sampling and comparison between sites or over time.

Selecting a subset of a population or area to estimate characteristics of the whole. Random or systematic sampling reduces bias and allows results to be generalised.