QCAA Earth & Environmental Science cheat sheet

Biodiversity has three levels: genetic diversity within a species, species diversity within a community, and ecosystem diversity across a landscape; each level is measured with different indices.

Species richness counts the number of species present; species evenness describes how similar abundances are. Two communities can share richness yet differ greatly in evenness and therefore in diversity index value.

Simpson's diversity index: D = 1 − Σ(n/N)², where n is the number of individuals of a species and N is the total number of individuals. Values near 1 indicate high diversity; values near 0 indicate dominance by one species.

Shannon–Wiener index: H' = −Σ pᵢ ln pᵢ, where pᵢ is the proportional abundance of species i. Higher H' means greater diversity; the index is sensitive to rare species, whereas Simpson's is dominated by common species.

Ecological succession: primary succession begins on new substrate with no soil (e.g. bare rock after glaciation, lava flows); secondary succession follows disturbance where soil and seed banks remain (e.g. after fire or land clearing).

In succession, species composition changes directionally: pioneer species are fast-growing, tolerant of harsh conditions and disperse widely; later seral stages feature longer-lived, shade-tolerant species until a climax community forms, subject to disturbance regime and climate.

Energy flows one way through trophic levels; only about 10% of energy transfers between levels, so biomass pyramids are usually upright, but inverted biomass pyramids occur in some aquatic systems where producers turn over rapidly.

Nutrient cycles differ from energy flow: matter is recycled. Carbon cycles through photosynthesis, respiration, combustion and decomposition; nitrogen is fixed biologically or industrially, then nitrified, assimilated and returned by denitrification.

Population growth: exponential growth occurs with unlimited resources (dN/dt = rN); logistic growth includes carrying capacity K (dN/dt = rN(K−N)/K). Limiting factors are density-dependent or density-independent.

Human impacts on ecosystems include habitat fragmentation, introduced species, pollution, overharvesting and climate change; these interact, and small fragmented populations lose genetic diversity through drift and inbreeding, raising extinction risk.

Earth is a system of four interacting spheres: atmosphere, hydrosphere, geosphere (lithosphere) and biosphere. A change in one sphere produces feedbacks in the others, e.g. volcanic aerosols reduce insolation and cool the surface.

Plate tectonics: divergent boundaries create new crust (mid-ocean ridges, rift valleys); convergent boundaries produce subduction zones, trenches, volcanic arcs and fold mountains; transform boundaries generate strike-slip earthquakes.

The rock cycle links igneous, sedimentary and metamorphic rocks. Sedimentary rocks preserve stratigraphic order (superposition), so fossils and layers record relative age; radiometric dating of igneous rocks gives absolute age.

Relative dating principles: superposition (older below), original horizontality, cross-cutting relationships (a feature cutting another is younger), and inclusions (fragments inside a rock are older than the host).

Absolute dating uses radioactive decay: N = N₀(1/2)^(t/t½), where t½ is the half-life. After one half-life, half the parent remains; after n half-lives, (1/2)ⁿ remains.

Earth's climate is driven by energy balance: incoming solar radiation versus outgoing longwave radiation. Greenhouse gases absorb and re-emit longwave radiation, raising surface temperature; albedo changes and aerosols modify this balance.

Climate proxies extend records beyond instrumental data: ice cores (CO₂ and δ¹⁸O), tree rings, coral growth bands, sediment cores and speleothems. Multiple proxies are cross-checked to reduce uncertainty.

Natural climate drivers include orbital cycles (Milankovitch), solar variability, volcanic eruptions and ocean circulation (e.g. ENSO); anthropogenic drivers include greenhouse gas emissions, land-use change and aerosols.

Renewable resources regenerate on human timescales (solar, wind, sustainably managed forests); non-renewable resources (fossil fuels, most minerals) form over geological timescales and are depleted by extraction.

Sustainability requires that resource use stays within regeneration rates and waste output stays within assimilation capacity. Indicators include ecological footprint, water scarcity indices and life-cycle assessment.