WACE ATAR Earth & Environmental Science cheat sheet

Earth's four spheres: geosphere (rock), atmosphere (gas), hydrosphere (water), biosphere (living matter); matter and energy exchange across their boundaries.

Geosphere layers by composition: crust (oceanic ~5-10 km, continental ~30-70 km), mantle (~2900 km), core (outer liquid, inner solid iron-nickel).

Mechanical layering: lithosphere (crust + rigid upper mantle, ~100 km) rides on the weak, partially molten asthenosphere.

Density increases with depth: crust ~2.7-3.0 g/cm3, mantle ~3.3-5.6, core ~9.9-13.0 g/cm3.

Isostasy: continental crust floats higher because it is thicker and less dense than oceanic crust; loading by ice or sediment causes subsidence.

Two heat sources drive geosystem processes: primordial accretion heat and radioactive decay (U-238, Th-232, K-40).

Geothermal gradient averages ~25-30 C per km in the crust; conductive heat flow is highest at mid-ocean ridges.

Seismic waves reveal internal structure: P waves travel through solids and fluids; S waves cannot pass liquid, proving a liquid outer core.

Mineral definition: naturally occurring, inorganic, crystalline solid with a definite chemical composition (or limited solid-solution range).

Physical identification tests: hardness (Mohs 1 talc to 10 diamond), cleavage vs fracture, lustre, streak, colour, specific gravity, crystal habit.

Silicate framework: one SiO4 tetrahedron; classification by polymerisation - isolated (olivine), single chain (pyroxene), double chain (amphibole), sheet (mica, clay), framework (quartz, feldspar).

Bowen's reaction series: crystallisation order from olivine/calcic plagioclase (high temperature) to quartz/muscovite/K-feldspar (low temperature).

Common rock-forming minerals: quartz, feldspars, micas, amphibole, pyroxene, olivine, calcite, dolomite, halite, gypsum.

Carbonates fizz in dilute HCl (calcite strongly, dolomite weakly); halite has cubic cleavage and salty taste.

Ore minerals: oxides and sulfides such as hematite (Fe2O3), magnetite (Fe3O4), chalcopyrite (CuFeS2), galena (PbS), sphalerite (ZnS).

Economic concentration requires a source, transport mechanism and trap; gangue is the unwanted mineral matter in an ore.

Igneous rocks crystallise from magma or lava; intrusive (plutonic) types are coarse-grained, extrusive (volcanic) types fine-grained or glassy.

Igneous classification by silica: felsic (granite, rhyolite), intermediate (diorite, andesite), mafic (gabbro, basalt), ultramafic (peridotite).

Sedimentary rocks: clastic (sandstone, shale, conglomerate) by grain size; chemical (limestone, rock salt); biogenic (coal, chalk).

Sedimentary structures as palaeoenvironment indicators: graded bedding, cross-bedding, ripple marks, mud cracks, fossils.

Metamorphic rocks form by heat and pressure: foliated (slate, schist, gneiss) vs non-foliated (marble, quartzite, hornfels).

Metamorphic grade increases from slate to phyllite to schist to gneiss; index minerals (chlorite, biotite, garnet, staurolite) mark zones.

Rock cycle pathways: melting, crystallisation, weathering and erosion, deposition and lithification, metamorphism, remelting.

Relative dating principles: superposition, original horizontality, lateral continuity, cross-cutting relationships, inclusions, faunal succession.

Wegener's continental drift evidence: matching coastlines, fossil and rock correlations, palaeoclimate indicators; rejected until seafloor spreading evidence.

Seafloor spreading: new oceanic crust forms at mid-ocean ridges; magnetic polarity stripes record reversals and are symmetrical about the ridge.

Three plate boundary types: divergent (constructive), convergent (destructive), transform (conservative).

Convergent outcomes depend on crust type: ocean-ocean gives island arcs; ocean-continent gives volcanic arcs and fold mountains; continent-continent gives collision mountains.

Driving forces: slab pull (dominant), ridge push, mantle convection; slab pull correlates with subducting plate age and density.

Hotspots produce age-progressive volcanic chains (e.g. Hawaii) that record plate motion direction and rate.

Plate velocity is calculated from hotspot or magnetic anomaly spacing: v = distance / time (commonly cm/yr).

Earthquake and volcano distribution defines plate margins; Wadati-Benioff zones dip beneath volcanic arcs at subduction zones.

Stress types: compression (folding, reverse faults), tension (normal faults), shear (strike-slip faults).

Folds: anticline (upward arch, oldest rocks in core), syncline (downward trough, youngest in core); limbs, axial plane and hinge line describe geometry.

Fault types: normal (hanging wall down, extension), reverse/thrust (hanging wall up, compression), strike-slip (lateral displacement).

Unconformities: angular (tilted then eroded), disconformity (erosion surface between parallel beds), nonconformity (sediment over igneous/metamorphic rock).

Geological time scale eras: Precambrian, Palaeozoic, Mesozoic, Cenozoic; boundaries marked by major extinctions and faunal turnover.

Radiometric dating: parent-daughter decay gives age; half-life is the time for half the parent to decay; use closed-system minerals.

Isotopic systems: U-Pb (zircon, millions to billions of years), K-Ar and Ar-Ar (volcanic rocks), C-14 (organic material under ~50,000 years).

Stratigraphic correlation uses index fossils (short-lived, wide geographic range) and marker beds to match sequences between locations.

Atmospheric composition (dry air): N2 ~78%, O2 ~21%, Ar ~0.93%, CO2 ~0.04%; water vapour is variable (0-4%).

Atmospheric layering: troposphere (weather, temperature decreases with height), stratosphere (ozone absorbs UV, temperature increases), mesosphere, thermosphere.

Lapse rates: environmental lapse rate averages ~6.5 C/km; dry adiabatic ~10 C/km; saturated adiabatic ~5-6 C/km.

Air rises when it is warmer and less dense than surroundings (unstable); stability determines cloud type and thunderstorm potential.

Coriolis effect deflects moving air right in the Northern Hemisphere and left in the Southern; geostrophic wind flows parallel to isobars.

Global circulation cells: Hadley (0-30 degrees), Ferrel (30-60), Polar (60-90); pressure belts and prevailing winds follow.

Climate controls: latitude, altitude, distance from ocean, ocean currents, prevailing winds, and topography (rain shadow).

Greenhouse effect: gases absorb and re-emit longwave infrared; enhanced warming scales with CO2, CH4, N2O and water vapour feedbacks.

Global water distribution: ~97.5% saline ocean water; of freshwater, ~69% is ice and glaciers, ~30% groundwater, under 1% surface water.

Hydrological cycle fluxes: evaporation, transpiration, condensation, precipitation, infiltration, runoff, groundwater flow; residence times differ greatly.

Ocean circulation: surface currents wind-driven (gyres, western boundary currents); thermohaline circulation driven by temperature and salinity density differences.

El Nino-Southern Oscillation: weakened trade winds and warm eastern Pacific water alter rainfall; La Nina is the reverse phase.

Groundwater: water table is the top of the saturated zone; aquifer vs aquitard; porosity (storage) differs from permeability (flow).

Cone of depression and pumping drawdown; saltwater intrusion occurs where freshwater lenses are over-extracted in coastal aquifers.

Stream discharge Q = cross-sectional area x velocity; hydrographs show lag time between rainfall and peak flow, shortened by urbanisation.

Water quality indicators: turbidity, dissolved oxygen, pH, salinity, nutrients (N, P), biological oxygen demand, heavy metals.

Carbon cycle reservoirs: atmosphere, oceans, biomass, soils, fossil fuels, carbonate rocks; fluxes include photosynthesis, respiration, combustion, weathering.

Nitrogen cycle steps: fixation (biological, lightning, industrial Haber-Bosch), nitrification, assimilation, ammonification, denitrification.

Phosphorus cycle is sedimentary: no gaseous phase; released by rock weathering, cycled by organisms, lost via sedimentation and runoff.

Soil profile horizons: O (organic), A (topsoil), B (subsoil accumulation), C (weathered parent material), R (bedrock).

Soil texture triangle classifies sand/silt/clay; clay and organic matter raise cation exchange capacity and water-holding capacity.

Soil formation factors (CLORPT): climate, organisms, relief, parent material, time.

Ecosystem trophic levels and the 10% rule: energy transfer efficiency is low, so biomass pyramids narrow upward.

Eutrophication sequence: nutrient enrichment, algal bloom, decomposition, oxygen depletion, fish kills, dead zone formation.

Renewable vs non-renewable resources: rate of use must not exceed rate of regeneration for renewables; non-renewables are finite.

Sustainability triple bottom line: environmental integrity, economic viability, social equity; intergenerational equity is central.

Environmental impact assessment steps: screening, scoping, baseline study, prediction, mitigation, monitoring, public review.

Resource management tools: quotas, total allowable catch, protected areas, rotational harvest, recycling, efficiency standards, cap-and-trade.

Climate change mitigation (reduce emissions) vs adaptation (adjust to impacts); examples include renewables, reforestation, sea walls, drought-resistant crops.

Biodiversity loss drivers: habitat fragmentation, invasive species, overexploitation, pollution, climate change.

Ecological footprint compares resource demand with biocapacity; overshoot occurs when footprint exceeds available productive land.

Monitoring design: baseline data, repeatable methods, control sites, adequate sample size, and consideration of natural variability.

Continental crust is felsic and buoyant; oceanic crust is mafic, denser, and subducts because it cools and thickens with age.

Ridge push acts as gravitational sliding down the elevated lithosphere; slab pull acts as negative buoyancy of the descending plate.

Subduction zone features: trench, accretionary wedge, forearc basin, volcanic arc, back-arc basin, Wadati-Benioff seismic zone.

Transform boundaries produce shallow-focus earthquakes (e.g. San Andreas); they do not create or destroy lithosphere.

Tectonic plate motion rates are typically 1-10 cm/yr; GPS geodesy measures absolute and relative plate velocities.

Earthquake magnitude (moment magnitude) is logarithmic: one unit increase equals about 32 times more energy release.

Volcanic styles: mafic low-viscosity lava gives shield volcanoes and flood basalts; felsic high-viscosity magma gives explosive stratovolcanoes.

Ophiolites preserve fragments of oceanic crust and upper mantle on land, evidence of ancient spreading and obduction.

Air pressure decreases with altitude; isobars close together indicate strong pressure gradient and stronger wind.

Frontal systems: cold front (steep, fast, heavy short rain), warm front (gentle slope, prolonged light rain), occluded front (cold catches warm).

Mid-latitude cyclones form along polar fronts; tropical cyclones require sea surface temperature above ~26.5 C and low wind shear.

Cloud types by altitude: cirrus (high, ice), altostratus/altocumulus (middle), stratus and cumulus (low), cumulonimbus (vertical, storms).

Relative humidity is the ratio of actual vapour pressure to saturation vapour pressure; dew point is the temperature of saturation.

Climate proxies: ice cores (CO2, isotopes), tree rings, corals, sediment cores, speleothems, historical records.

Milankovitch cycles (eccentricity, obliquity, precession) pace glacial-interglacial cycles; feedbacks amplify or damp them.

Albedo contrasts: ice and snow high albedo, ocean and forest low; ice-albedo feedback amplifies warming.

Ocean salinity averages ~35 g/kg; it is controlled by evaporation, precipitation, river input, and sea ice formation/ melting.

Temperature-salinity (T-S) diagrams identify water masses; density increases with higher salinity and lower temperature.

Upwelling brings nutrient-rich deep water to the surface, supporting high productivity (e.g. Peru, Benguela).

Watershed (catchment) boundaries are drainage divides; stream order and drainage density describe network structure.

Groundwater flow follows Darcy's law: Q = K A (dh/dL), where K is hydraulic conductivity and dh/dL is the hydraulic gradient.

Aquifer types: unconfined (water table) vs confined (artesian, under pressure); recharge zones must be protected.

Water scarcity is physical (supply shortage) or economic (lack of infrastructure, finance); both require different management responses.

Desalination and water recycling reduce supply pressure but consume energy and produce brine or concentrate waste.

Biogeochemical cycles are driven by solar energy and gravity; reservoirs are atmosphere, hydrosphere, lithosphere and biosphere.

Human perturbations: fossil fuel combustion (carbon), fertiliser use (nitrogen, phosphorus), land clearing (carbon, nitrogen), mining (metals, sulfur).

Carbonate-silicate cycle regulates long-term CO2: weathering consumes CO2, carbonate precipitation and volcanism release it.

Nitrogen fixation is the rate-limiting step of the nitrogen cycle in most ecosystems; legumes use Rhizobium symbionts.

Phosphorus is often the limiting nutrient in freshwater; nitrogen often limits marine systems.

Ecological succession: primary (bare substrate) vs secondary (disturbed, soil present); pioneer species to climax community.

Trophic cascades occur when removal of a top predator alters lower trophic levels and ecosystem structure.

Ecosystem services: provisioning (food, water), regulating (climate, flood control), cultural, and supporting (nutrient cycling, soil formation).

Anthropocene signals: elevated CO2, radionuclides from testing, plastics, concrete, and altered nitrogen and phosphorus fluxes.

Proxy evidence for recent change: instrumental records, satellite data, ice cores, sediment cores, coral chemistry, tree rings.

Resource classification: reserves (known, economically extractable) vs resources (potential, not currently economic).

Life cycle assessment quantifies impacts from extraction, manufacture, use, and disposal; functional unit is essential for comparison.

Waste hierarchy: avoid, reduce, reuse, recycle, recover energy, dispose; higher tiers give greater environmental benefit.

Fisheries management: maximum sustainable yield is set below carrying capacity; quotas, size limits, and marine protected areas support recovery.

Mining impacts: acid mine drainage from sulfide oxidation, tailings dams, subsidence, and rehabilitation to stable landforms.

Sustainability indicators: water use efficiency, carbon intensity, biodiversity index, soil erosion rate, recycling rate.