Extremadura PAU Geology and Environmental Sciences Exam cheat sheet

Geology is a historical science: it builds testable hypotheses from rocks, fossils, isotopes and geophysics, because direct experiment on the whole planet is impossible.

Principle of uniformitarianism (Hutton, Lyell): present-day processes, acting over long times, explain ancient rocks; actualism adds that rates and conditions may differ in the past.

Steno's principles: superposition (younger above older in undisturbed sequences), original horizontality, lateral continuity, and cross-cutting relationships (a cut is younger than what it cuts).

Relative age order: superposition, cross-cutting, inclusion (clasts are older than the rock containing them), and fossil succession; absolute age from radiometric decay (e.g. ⁴⁰K→⁴⁰Ar, ²³⁸U→²⁰⁶Pb, ¹⁴C for <~50 ka).

Earth's internal layers by composition: crust (oceanic ~5–10 km, basaltic; continental ~30–70 km, granitic), mantle (to ~2900 km, peridotite), core (Fe-Ni; liquid outer core, solid inner core).

Layers by mechanical behaviour: lithosphere (crust + uppermost mantle, rigid, ~100 km), asthenosphere (partially molten, ductile, flows), mesosphere, outer core, inner core.

Seismic evidence: P waves (compressional, travel through solids and fluids, ~6–8 km/s in crust) and S waves (shear, blocked by liquids) define the Moho and the core-mantle boundary; S-wave shadow zone proves a liquid outer core.

Isostasy: lithospheric plates float on the asthenosphere; continental crust is thicker and less dense, so it stands higher (Airy model); post-glacial rebound shows mantle flow.

Geomagnetic field is generated by convection of liquid iron in the outer core (dynamo); magnetic stripes on the seafloor record reversals and support seafloor spreading.

Mineral definition: naturally occurring, inorganic, solid, definite chemical composition (or limited solid solution) and ordered internal structure; ~4000 known species, silicates dominate the crust.

Diagnostic mineral properties: hardness (Mohs 1 talc to 10 diamond), cleavage vs fracture, lustre, colour and streak, density, crystal habit, reaction with dilute HCl (calcite), magnetism, taste.

Silicate structures control properties: isolated tetrahedra (olivine), chains (pyroxene, amphibole), sheets (micas, clays), frameworks (quartz, feldspars); more shared oxygens = higher Si:O ratio and generally higher stability.

Bowen's reaction series: mafic minerals crystallize at higher temperature (olivine → pyroxene → amphibole → biotite) and felsic last (feldspar → muscovite → quartz); explains magma differentiation.

Igneous classification by SiO₂ and texture: plutonic/volcanic; felsic (granite/rhyolite), intermediate (diorite/andesite), mafic (gabbro/basalt), ultramafic (peridotite); slow cooling = coarse grains.

Sedimentary rocks: clastic (conglomerate, sandstone, shale by grain size), chemical (limestone, rock salt, chert) and organic (coal, some limestone); bedding, cross-bedding, ripples and fossils are key structures.

Metamorphic rocks: foliated (slate → schist → gneiss, increasing grade) and non-foliated (marble from limestone, quartzite from sandstone); index minerals (chlorite, biotite, garnet, staurolite, sillimanite) mark grade.

Rock cycle links the three types through melting, weathering, erosion, burial and metamorphism; any rock type can transform into any other; no fixed starting point.

Uses: limestone for cement, gypsum for plaster, clay for ceramics, granite and marble as ornamental stone, halite for salt, metal ores (hematite, galena, sphalerite) for industry, aggregates for construction.

Plate tectonics: rigid lithospheric plates move over the asthenosphere at 1–10 cm/yr, driven mainly by slab pull and ridge push, with mantle convection as the underlying engine.

Plate boundaries: divergent (mid-ocean ridges, rifts - normal faults, basaltic volcanism), convergent (subduction - deep earthquakes, andesitic arcs; collision - fold mountains), transform (strike-slip, e.g. San Andreas).

Subduction produces a Wadati-Benioff zone of deepening earthquakes, an accretionary wedge, a volcanic arc and a back-arc basin; ocean trenches mark the downgoing slab.

Magma forms by decompression melting at ridges and hot spots, by addition of water lowering the melting point at subduction zones, and by crustal heating in rifts.

Magma properties: higher SiO₂ and dissolved gas = higher viscosity and more explosive eruption; low-viscosity basaltic magma gives effusive flows and shield volcanoes; stratovolcanoes are andesitic.

Volcanic hazards and products: lava flows, pyroclastic falls and flows, lahars, ash on aviation; products include pumice, tuff, obsidian and columnar-jointed basalt.

Metamorphism types: regional (mountain belts, directed pressure, foliation), contact (around intrusions, non-foliated hornfels), dynamic (fault zones, mylonite), burial and hydrothermal.

Metamorphic grade rises with temperature and pressure; index minerals in pelites define zones; metamorphic facies (greenschist, amphibolite, granulite, blueschist, eclogite) record P-T conditions.

Earthquakes occur mainly at plate boundaries from elastic rebound on faults; magnitude (M) measures energy released, intensity (EMS/MM) measures observed damage; focus vs epicentre.

Weathering is in situ breakdown: physical (freeze-thaw, salt crystallization, thermal expansion, root wedging), chemical (hydrolysis of feldspars to clays, oxidation, carbonation/dissolution of limestone) and biological.

Climate controls weathering style: chemical weathering dominates in hot humid climates (thick laterite/kaolinite soils); physical weathering dominates in cold or arid climates (frost shattering, angular debris).

Karst: CO₂ + H₂O + CaCO₃ ⇌ Ca²⁺ + 2HCO₃⁻; dissolution produces caves, sinkholes, dolines, poljes and underground drainage; reprecipitation forms stalactites and stalagmites.

Erosion agents: water (sheet, rill, gully, river), wind (deflation, abrasion, dunes, loess), ice (glacial plucking and abrasion, U-shaped valleys, moraines, cirques), gravity (mass wasting: creep, slide, flow, fall).

Transport modes: dissolved load, suspended load, bedload (saltation, traction) in rivers; sorting and rounding increase with transport distance and time.

Deposition occurs when energy falls (gradient decreases, water enters a lake/sea, wind drops); larger and denser clasts settle first - graded bedding records waning energy.

River profile: erosion dominates in the upper course (V-valleys, waterfalls), transport in the middle (meanders, floodplain, point bars), deposition in the lower course (deltas, levees, oxbow lakes).

Sedimentary structures as palaeoenvironment indicators: cross-bedding (dunes, ripples), graded bedding (turbidites), mud cracks (subaerial exposure), ripple marks (current or wave action), fossils.

Diagenesis converts sediment to rock: compaction, cementation (calcite, silica, iron oxide), recrystallization and lithification; porosity and permeability control groundwater and hydrocarbon storage.

Atmospheric composition (dry air): ~78% N₂, 21% O₂, 0.93% Ar, 0.04% CO₂; variable water vapour (0–4%) is the main greenhouse gas by mass effect.

Vertical structure: troposphere (weather, temperature falls ~6.5 °C/km), stratosphere (ozone layer, temperature rises), mesosphere, thermosphere; pressure decreases exponentially with altitude.

Insolation is uneven: equatorial surplus and polar deficit drive atmospheric and oceanic circulation; the Coriolis effect deflects moving air (right in N hemisphere, left in S).

Global circulation cells: Hadley, Ferrel and Polar cells produce trade winds, westerlies, polar easterlies and the intertropical convergence zone; jet streams form at cell boundaries.

Greenhouse effect: gases (H₂O, CO₂, CH₄, N₂O, O₃, CFCs) absorb outgoing infrared radiation and re-emit it, warming the surface by roughly 33 °C above the blackbody value.

Climate vs weather: climate is the long-term statistical state (typically 30-year normals); climate is controlled by latitude, altitude, distance from sea, ocean currents, relief and atmospheric circulation.

Climate feedbacks: positive (ice-albedo loss, water vapour, permafrost methane release) amplify change; negative (increased cloud albedo, enhanced CO₂ uptake by oceans and vegetation) damp it.

El Niño–Southern Oscillation: weakened trade winds and warm eastern Pacific water alter rainfall worldwide; La Niña is the opposite phase; both are short-term (2–7 year) variability.

Ozone depletion is a separate problem from warming: CFCs release chlorine that destroys stratospheric O₃ over polar regions in spring; the Montreal Protocol addresses it.

Water cycle fluxes: evaporation and transpiration → condensation → precipitation → interception, infiltration, runoff and groundwater flow → oceans; residence times range from days (atmosphere) to millennia (deep groundwater, ice).

Distribution of water: ~97% saline ocean water; of freshwater, ~69% in glaciers and ice caps, ~30% groundwater, <1% in lakes and rivers and a tiny fraction in the atmosphere.

Watershed (cuenca hidrográfica): the area drained by a river and its tributaries, bounded by divides; river regime describes seasonal flow variation (nival, pluvial, mixed).

River discharge Q = cross-sectional area × mean velocity; hydrographs show lag time between rainfall and peak flow, shortened by impermeable surfaces and deforestation.

Groundwater: zone of aeration, water table, zone of saturation; aquifer types (free vs confined), porosity vs permeability; recharge areas must be protected from pollution.

Karst and thermal waters: limestone aquifers transmit water rapidly through conduits; mineral and thermal springs arise from deep circulation and heating, used in balneotherapy.

Marine water: average salinity ~35 g/L (3.5%), dominated by Na⁺ and Cl⁻; temperature and salinity control density, driving thermohaline circulation (deep ocean conveyor).

Tides result from gravitational attraction of the Moon and Sun plus centrifugal effects; spring tides at new and full moon, neap tides at quarter phases.

Waves are wind-driven energy moving through water; they refract, shoal and break near coasts, causing longshore drift and coastal erosion or deposition.

Biosphere: the zone occupied by life, from deep ocean and crustal microbes to the upper atmosphere; life modifies the atmosphere (oxygenic photosynthesis) and geochemical cycles.

Biogeochemical cycles: carbon (photosynthesis/respiration, ocean uptake, fossil fuel release), nitrogen (fixation, nitrification, denitrification), phosphorus (no gaseous phase, limiting nutrient), water and oxygen.

Soil is a three-phase system: mineral matter (~45%), organic matter (~5%), water and air in pore spaces; soil profile horizons O, A, E, B, C, R.

Soil formation factors (Jenny): climate, organisms, relief, parent material and time; texture (sand, silt, clay) determines water retention, aeration and fertility.

Soil degradation: erosion, salinization (irrigation in arid areas), compaction, loss of organic matter, contamination by heavy metals and pesticides; Mediterranean soils are prone to erosion after fires.

Ecosystem structure: producers, consumers, decomposers; trophic levels and food webs; energy flows one way (~10% transferred between levels) while matter cycles.

Biodiversity and endemism: Mediterranean and mountain habitats host high endemism; Extremadura holds important steppe bird populations (great bustard, little bustard) and dehesa habitat.

Succession: primary (bare substrate, e.g. lava, dunes) and secondary (after fire or abandonment) leads to a climax community; disturbance resets or diverts succession.

Human pressures: habitat fragmentation, invasive species, overexploitation, pollution and climate change are the main drivers of biodiversity loss.

Resource classification: renewable (solar, wind, hydro, biomass, geothermal) vs non-renewable (fossil fuels, nuclear fuels, most minerals); reserves are the economically extractable part of a resource.

Energy conversions and limits: fossil fuels release energy stored over millions of years; combustion produces CO₂, SO₂, NOₓ and particulates; SO₂ and NOₓ cause acid rain.

Renewable impacts are not zero: hydro alters river regimes and blocks fish migration; wind turbines affect birds and landscapes; solar farms occupy land; biomass competes with food.

Water resources: overexploitation of aquifers causes water-table decline, land subsidence and saltwater intrusion in coastal aquifers; irrigation is the largest consumptive use.

Mining and soil impacts: open-pit mining destroys landscapes, generates acid mine drainage (pyrite oxidation) and tailings; restoration requires reshaping, topsoil replacement and revegetation.

Waste management hierarchy: prevention > reuse > recycling > energy recovery > landfill; hazardous waste needs controlled storage; organic waste in landfills produces methane.

Environmental impact assessment (EIA): identifies, predicts and mitigates impacts before authorization; includes alternatives, monitoring and public participation.

Sustainability: meeting present needs without compromising future generations; indicators include ecological footprint, carbon footprint and carrying capacity.

Circular economy and energy transition: reduce material throughput, extend product life, recycle critical metals; decarbonizing electricity, transport and heating is central to climate goals.

Risk = hazard × exposure × vulnerability; hazard is the potentially damaging event, vulnerability the conditions that make people or assets susceptible; risk is not the same as hazard.

Natural hazards: earthquakes, volcanic eruptions, tsunamis, floods, landslides, droughts, storms and wildfires; each has a return period and a spatial distribution linked to geology and climate.

Flood risk factors: intense rainfall, impermeable or saturated soils, deforestation, urban sealing, floodplain occupation, channel narrowing; mitigation includes reforestation, retention basins, dikes and land-use zoning.

Landslide risk factors: steep slopes, weak or clay-rich lithology, heavy rain, earthquakes, deforestation and construction loading; mitigation includes drainage, retaining walls and slope stabilization.

Seismic risk depends on hazard (fault proximity, local amplification), exposure and vulnerability; construction codes and microzonation reduce damage; prediction remains impossible.

Drought and desertification: arid and semi-arid areas of Extremadura are vulnerable; overgrazing, deforestation and poor irrigation accelerate soil degradation (UNCCD framework).

Wildfire: Mediterranean summers with high temperature, low humidity and wind favour fire; risk reduction uses fuel management, firebreaks, early detection and post-fire erosion control.

Climate change adaptation vs mitigation: mitigation cuts greenhouse gas emissions; adaptation reduces vulnerability (early warning, water efficiency, resistant crops, coastal planning).

Protected areas and planning instruments (national parks, Natura 2000, river basin plans, civil protection plans) integrate risk prevention with conservation and land-use management.