GeologyQ&A by dot point

Basin analysis: the definition of a sedimentary basin and the mechanisms of subsidence (thermal subsidence after lithospheric stretching, flexural loading and sediment loading); the concept of accommodation space and its control by subsidence and sea-level change; the main basin types (rift, passive-margin and foreland); the use of vertical facies successions and burial-history curves to reconstruct basin evolution.

Earth structure: the layered internal structure of the Earth (crust, mantle, outer core and inner core) and the contrasts between oceanic and continental crust; the seismic evidence for the layering (changes in wave velocity at boundaries such as the Moho); the P and S wave shadow zones as evidence for a liquid outer core; the link between the core and the Earth's magnetic field.

Sedimentary environments: the concept of facies as a body of rock reflecting a particular depositional environment; sedimentary structures (bedding, cross-bedding, graded bedding, ripple marks and desiccation cracks) and their interpretation; the characteristics of the main environments (fluvial, deltaic, shallow marine, deep marine and desert); the construction and interpretation of sedimentary logs to reconstruct environmental change.

Structural measurement: the definition and measurement of true dip, apparent dip and strike; the recording of orientation data; the calculation of the true (vertical and stratigraphic) thickness of a bed from its outcrop width, dip and the slope of the ground; the use of trigonometry in structural calculations.

Engineering geology: the engineering properties of rocks and soils (strength, jointing and discontinuities, weathering and the behaviour of clays, sands and gravels); the purpose and methods of site investigation (desk study, boreholes, trial pits and core logging); the ground conditions that cause problems for foundations (weak or compressible soils, swelling clays, solution cavities in limestone, made ground and high groundwater); the role of foundations and the ground model.

Fieldwork and maps: the recording of field observations (field sketches, measurements and logged sections); the interpretation of geological maps (outcrop patterns, the rule of Vs and the relationship between topography and dip); the construction of a geological cross-section from a map; the recognition of structures (folds, faults and unconformities) on maps and cross-sections.

Earthquake hazards: the primary and secondary hazards (ground shaking, surface rupture, liquefaction, landslides and tsunamis); the distinction between hazard, vulnerability, exposure and risk; the factors that determine the impact of an earthquake (magnitude, depth, ground conditions, population density, building design and preparedness); monitoring and mitigation (building codes, land-use planning, early-warning systems and education); the limits of earthquake prediction.

Mass movement: the types of slope failure (rockfall, translational and rotational slides, slumps and debris flows); the balance of driving and resisting forces on a slope; the factors that trigger failure (slope angle, rock and soil type, water content, discontinuities, weathering, earthquakes and human activity); the recognition of warning signs; the engineering methods used to stabilise slopes and reduce risk.

Volcanic hazards: the hazards of an eruption (lava flows, pyroclastic flows, ash falls, lahars, volcanic gases and sector collapse) and how they relate to magma type and the Volcanic Explosivity Index; the methods of monitoring a volcano (seismicity, ground deformation, gas emissions and thermal anomalies); the use of hazard maps, exclusion zones and evacuation to mitigate risk; the comparison with earthquakes in terms of predictability.

Evolution and the fossil record: evidence for evolution from the fossil record (morphological change through time, transitional forms, adaptive radiation); the models of evolutionary change (gradualism versus punctuated equilibrium); mass extinctions and their causes and effects (for example the end-Permian and end-Cretaceous events); the incompleteness and biases of the fossil record.

Fossils: the conditions that favour preservation (rapid burial, anoxia, hard parts, fine sediment); the modes of preservation (moulds and casts, permineralisation, carbonisation, and preservation in amber or ice); the properties of a good index (zone) fossil (abundant, widespread, easily recognised, short stratigraphic range); the distinction between body and trace fossils.

Radiometric dating: radioactive decay of unstable parent isotopes to stable daughter isotopes; the concept of half-life as a constant; the use of parent-to-daughter ratios to calculate absolute ages; the main isotopic systems (uranium-lead, potassium-argon and carbon-14) and their suitable age ranges; the assumptions and limitations of radiometric dating; the combination of absolute and relative dating.

Relative dating: the principles used to order geological events (superposition, original horizontality, cross-cutting relationships, included fragments and faunal succession); the recognition of way-up evidence; the application of these principles to construct the geological history of a cross-section, including faults, intrusions and unconformities.

The geological record: the hierarchy of the geological time scale (eon, era, period, epoch) and the major divisions (Precambrian and the Phanerozoic eras); correlation of strata by lithostratigraphy (matching rock units) and biostratigraphy (matching fossils and biozones); the use of marker horizons such as volcanic ash bands; the distinction between rock units (systems) and time units (periods).

Earthquakes: focus and epicentre; the elastic rebound mechanism; the types of seismic wave (P, S and surface waves) and their properties; magnitude (the logarithmic Richter and moment magnitude scales) versus intensity (Modified Mercalli); the use of P and S wave arrival times and travel-time graphs to locate an epicentre by triangulation.

Geological structures: the response of rocks to stress (folds and faults); fold elements and types (anticline and syncline, limb, hinge and axial plane); fault types and the stress regime they record (normal from tension, reverse and thrust from compression, strike-slip from shear); joints; dip and strike; the recognition and significance of unconformities (angular unconformity, disconformity and nonconformity).

Plate margins: the processes and features of constructive (divergent), destructive (convergent) and conservative (transform) margins; the sub-types of destructive margin (ocean-continent, ocean-ocean and continent-continent collision); the Benioff zone and subduction; the characteristic rocks, structures, earthquakes and volcanoes produced at each margin type.

Plate tectonics: the development of the theory from continental drift (Wegener's evidence) through sea-floor spreading to plate tectonics; the evidence of palaeomagnetism and symmetrical magnetic striping at mid-ocean ridges; the increasing age of oceanic crust away from ridges; the driving mechanisms of mantle convection, ridge push and slab pull.

Volcanism: the control of magma composition (silica content), viscosity and dissolved gas on eruption style; the contrast between basaltic effusive eruptions and andesitic or rhyolitic explosive eruptions; volcanic products (lava, tephra, pyroclastic flows and gases); volcanic landforms (shield volcanoes, stratovolcanoes, calderas and fissures); the link between volcanism and plate setting.

Groundwater: porosity and permeability and how they differ between rock types; aquifers, aquitards and the water table; confined and unconfined aquifers; the calculation of porosity from pore and total volumes; the use of a simple form of Darcy's law to relate groundwater discharge to hydraulic conductivity, hydraulic gradient and area; the issues of over-abstraction and contamination.

Hydrocarbons: the petroleum system (source rock, maturation, migration, reservoir rock, trap and seal); the formation of oil and gas from organic-rich source rocks by burial and heating; the properties needed in a reservoir (porosity and permeability) and a seal (low permeability); the types of trap (structural and stratigraphic); the formation of coal from plant material with increasing rank.

Ore formation: the processes that concentrate metals into economic mineral deposits (hydrothermal vein and disseminated deposits, magmatic segregation, placer deposits and residual deposits); the conditions and host rocks typical of each; the distinction between ore and gangue and the idea that a deposit is economic only if the metal is concentrated well above its crustal average.

Mining geology: the economic terms (ore grade, cut-off grade, reserves and resources) and the factors affecting whether a deposit is mined (grade, tonnage, depth, location, technology, price and environmental constraints); the calculation of contained metal from grade and tonnage; the extraction methods (open-pit and underground) and the geological and environmental issues of mining (waste, tailings and acid mine drainage).

Igneous processes: Bowen's reaction series as the order in which silicate minerals crystallise from a cooling magma; the discontinuous (olivine to biotite) and continuous (calcium-rich to sodium-rich plagioclase) branches; the use of the series to explain fractional crystallisation, magma differentiation and the resistance of minerals to weathering.

Igneous bodies: the forms of intrusive igneous bodies (batholiths, dykes, sills and laccoliths) and their relationship to the country rock (concordant versus discordant); chilled margins, baked margins and contact metamorphic aureoles as evidence of intrusion; the recognition of extrusive forms (lava flows and their cross-cutting relationships) and the use of these relationships to establish relative age.

Igneous rocks: classification by silica content (acid, intermediate, basic and ultrabasic) and by grain size (coarse-grained intrusive, fine-grained extrusive); the relationship between cooling rate and crystal size; igneous textures (phaneritic, aphanitic, porphyritic, glassy and vesicular) and what they show about the cooling history; naming common igneous rocks such as granite, gabbro, basalt and rhyolite.

Minerals and rocks: the structure of the silicate minerals based on the silica tetrahedron; the silicate groups (isolated, chain, sheet and framework silicates) and how the degree of polymerisation links to composition; the physical properties (colour, lustre, hardness, cleavage, fracture, streak, density and habit) used to identify the common rock-forming minerals quartz, feldspar, mica, olivine, pyroxene and amphibole in hand specimen.

Metamorphic rocks: the agents of metamorphism (heat, pressure and chemically active fluids); the types of metamorphism (regional, contact and dynamic) and their settings; the development of foliation under directed pressure; metamorphic grade and the prograde sequence from mudstone (slate, phyllite, schist, gneiss); the use of index minerals (chlorite, garnet, kyanite, sillimanite) to indicate grade.

Sedimentary rocks: the stages from sediment to rock (deposition, compaction and cementation as lithification); the classification of sedimentary rocks into clastic (by grain size, from conglomerate to mudstone), chemical (precipitates such as evaporites) and biogenic or biochemical (limestone and coal); the description of clastic texture using grain size, sorting and roundness.

The rock cycle: the continuous transformation between igneous, sedimentary and metamorphic rocks; the processes that link them (crystallisation, weathering, erosion, transport, deposition, lithification, metamorphism, melting, uplift and exposure); the role of plate tectonics in driving the cycle; recognising that any rock type can be converted into any other.

Surface processes: mechanical weathering (freeze-thaw, exfoliation and abrasion) and chemical weathering (solution, hydrolysis and oxidation); the difference between weathering and erosion; transport by water, wind and ice and its effect on the rounding and sorting of sediment; how the maturity and texture of a sediment record its transport history.