Topic 1: ELEMENTS, MINERALS AND ROCKS Key Idea 1: The Earth is composed of rocks which have distinctive mineralogies and textures Knowledge and understanding Geological techniques and skills Comments a. The Earth’s elements may be classified according to the Goldschmidt system (lithophile, siderophile, chalcophile, atmophile) which aids subdivision of the Earth on the basis of geochemistry (atmosphere, hydrosphere, crust, mantle and core). Candidates should be aware of the four-fold classification and its delineation and be able to name at least one element from each group. lithophile: elements that combine well with oxygen and are concentrated in the crust; siderophile: ‘iron loving’ elements typical of the core; chalcophile: ‘ore loving’ elements which combine well with sulfur near the Earth’s surface; atmophile: volatile elements within liquids and gases on or above the Earth’s surface. b. The bulk composition of the Earth is comparable with that of undifferentiated meteorites (chondrites). Candidates should know that evidence for the internal composition of the Earth partly comes from chondrite meteorites. c. The Earth’s crust is composed of eight main elements. Recognition of the relative abundance of O, Si, Al, Fe, Ca, Na, K and Mg in the crust and the role of the silicates as rock-forming minerals. Candidates should know that 99% of the Earth’s crust (by weight) is made up of just 8 elements and their relative order of abundance.
Knowledge and understanding Geological techniques and skills Comments d. Silicates are the commonest rock- forming minerals and are built from silicon- oxygen tetrahedral (single, chain, sheet and framework silicates). Simple analysis of silicate mineral structures from models and diagrams. Candidates should know the chemical structure of silicates as it relates to the physical properties of minerals (e.g. crystal shape, hardness and cleavage) rather than details of the chemical variations between minerals. As exemplified by olivine (single tetrahedra), augite/pyroxene (single chain),hornblende/amphibole (double chain), micas (sheet) and quartz/feldspar (framework). e. Minerals are naturally occurring inorganic chemical compounds or elements with compositions that may be expressed as chemical formulae. Minerals have distinct chemical compositions, atomic structures and physical properties by which they may be identified. P1: Investigation of diagnostic properties of minerals: colour, crystal shape, cleavage, fracture, hardness, relative density, streak, lustre, reaction with cold dilute (0.5 mol dm−3) hydrochloric acid. P2: Measurement of the density of minerals. Recognition, using appropriate tests, of the following rock- forming minerals (as specified on the mineral data sheet available for use in the examination) from their diagnostic properties: quartz, calcite, feldspars (orthoclase, plagioclase), augite, hornblende, olivine, micas (biotite, muscovite), haematite, galena, pyrite, chalcopyrite, fluorite, barite, halite, gypsum, garnet, chiastolite/andalusite. Candidates should be able to investigate the physical/chemical properties of minerals (including unfamiliar minerals) in the laboratory and field. Candidates should be able to measure the density of minerals using an appropriate technique and evaluate the accuracy of such calculations. Candidates will be required to use a mineral data sheet of diagnostic mineral properties in their identification of the stated minerals.
Knowledge and understanding Geological techniques and skills Comments P3: Application of classification systems using distinguishing characteristics to identify unknown minerals. Candidates should be able to use flow charts to classify minerals (including unfamiliar minerals) from their observed physical/chemical properties. f. Rocks are composed of aggregates of minerals, pre-existing rocks or fossils. g. Igneous, sedimentary and metamorphic rocks display differences of composition and texture that reflect their mode of origin. Observation and investigation of hand specimens of a variety of rocks (including sampling in the field) in order to: identify and interpret component composition interpret colour and textures (crystalline/clastic; crystal or grain size/shape; sorting; foliation; mineral alignment/bedding/cryst- alline banding) and hence deduce the mode of origin of the rock as igneous, metamorphic or sedimentary. P4: Production of scaled annotated scientific drawings of rock samples from hand samples using a light microscope, or hand lens observation. Use and manipulation of the magnification formula magnification = size of image size of real object Candidates should be able to determine the origin of igneous, sedimentary and metamorphic rocks from their differing textures and mineralogies (including unfamiliar rocks) in the laboratory and field. Scientific drawings to include samples in the laboratory and the field using appropriate scales.
Knowledge and understanding Geological techniques and skills Comments Surface materials are transported by a range of erosional agents and are deposited as sediments: erosion (abrasion, attrition) transport (traction, saltation, suspension, solution) deposition selectively concentrates products in particular environments – grain size related to energy of depositional environment; dominance of quartz and muscovite in coarse fraction and clay minerals in fine fraction; flocculation; precipitation. Recognition and use of appropriate units in calculations. Construction and interpretation of frequency tables and diagrams, bar charts and histograms. Finding of arithmetic means. Understanding of the principles of sampling as applied to scientific data. Understanding of the measures of dispersion, including standard deviation and interquartile range. The surface processes part of the rock cycle facilitates, (though not exclusively) training in, and assessment of, some mathematical skills. For exemplification of mathematical skills see Mathematical Guidance for AS Geology. d. Different sedimentary environments may be identified by diagnostic sedimentary structures, rock textures, mineralogy and fossil content. Description of sedimentary rocks in hand specimens, rock exposures and diagrams/photographs from observation of their colour, texture (use of sediment comparators to determine grain size, shape and sphericity), (coarse >2 mm, fine <1/16 mm), reaction with 0.5 mol dm−3 hydrochloric acid, mineralogy and other diagnostic features.
Knowledge and understanding Geological techniques and skills Comments e. A study of fluvial, marine, and aeolian sediments demonstrates these differences. Investigation of textures of sediments from different depositional environments. P5: Production of full rock description of macro and micro features from hand specimens and unfamiliar field exposures of sedimentary rocks in order to interpret component composition, colour and textures, to identify rock types and to deduce their environment of deposition. P6: Construction of graphic logs using appropriate scale and symbol sets for unfamiliar geological sequences and exposures to record data relevant to an investigation. P7: Use of photomicrographs to identify minerals and rock textures of sedimentary rocks in order to identify rock types and to deduce their environment of deposition. Interpretation of maps, photographs and graphic logs showing the following sedimentary features: bedding, cross-bedding, graded bedding, laminations, desiccation features, ripple marks (symmetrical and asymmetrical), sole structures (load/flame, flute cast). Candidates should be aware of the link between process and product in their studies of the stated sedimentary environments: fluvial (rivers, deltas alluvial fans and playa lakes) aeolian (wind dominated e.g. desert dunes) marine (shallow water – lagoon/reef/beach systems) marine (deep water – submarine fan turbidites) Candidates should be able to explain the formation of the stated sedimentary structures.
Knowledge and understanding Geological techniques and skills Comments Sedimentary rocks exhibit differences in texture which influences porosity and permeability: grain angularity, sphericity, size, sorting, which reflects: the nature of rocks from which they were derived conditions of climate, weathering, erosion and deposition operating during their formation post-depositional factors as sediments are formed into sedimentary rocks: diagenesis and lithification (compaction, recrystallisation, cementation, pressure solution). Investigation of the concept of ‘sediment maturity’. Immature sedimentary rocks characterised by a wide range of mineral compositions and/or lithic clasts; mature sedimentary rocks with restricted mineralogies dominated by mineral species resistant to weathering and erosional processes. Understanding that y = mx + c represents a linear relationship. Candidates should be aware of the range of texture in descriptive terms (as used on a grain size comparator): angularity – very angular to well rounded sphericity – high to low sphericity size – reference to the Wentworth scale sorting – very well to poorly sorted For exemplification of mathematical skills see Mathematical Guidance for AS Geology. The mathematical skills identified are not exclusive to this section of the specification.
Knowledge and understanding Geological techniques and skills Comments Partial melting of rock at depth to form magma occurs in a number of different interplate and intraplate tectonic settings: beneath divergent plate margins – partial melting of mantle rocks generates basaltic magma near to convergent plate margins – partial melting of subducted oceanic lithosphere and overlying lithospheric wedge generates andesitic magma in mantle plumes (hotspots) – partial melting of mantle rocks generates basaltic magma in deeply buried lower continental crust during orogeny – melting and assimilation of crustal material generates granitic magma. Investigation of the role of rising convection cells in decompression melting. Investigation of global distribution of mantle plumes from maps. Volcanic hazards result from: blast/explosion ash fall, pyroclastic flows (nuées ardentes) and gases lava flows debris flows and mudflows (lahars). Investigation, using geological data from a wide variety of volcanic monitoring techniques (including ground deformation, gravity and thermal anomalies, gas emissions and seismic activity), of the risk of volcanic hazards and the extent to which they can be managed and controlled in order to reduce risk. Candidates are expected to have studied specific examples of the stated hazards and monitoring techniques but will not be required to recall details of these examples in an assessment.
Knowledge and understanding Geological techniques and skills Comments e. The nature of the volcanic hazard is linked to the composition, viscosity and gas content of the magma. Candidates are expected to have studied the hazards associated with explosive and effusive activity and their links to silica and gas content that affects viscosity. f. Metamorphism involves mineralogical and/or textural change of pre- existing rocks in response to changes in temperature and/or pressure. Interpretation of the following metamorphic features using simplified geological maps and photographs: contact aureoles, metamorphic foliations. Candidates should be aware of the concept of metamorphic grade. Contact (thermal) and regional metamorphism produce distinctive mineralogical and textural changes: non-foliated in contact metamorphism foliation (slaty cleavage, schistosity and gneissose banding) in regional metamorphism. Understanding that y = mx + c represents a linear relationship. P10: Production of full rock description of macro and micro features from hand specimens and/or unfamiliar field exposures of metamorphic rocks in order to interpret component composition, colour and textures, to identify rock type and to deduce the temperature and pressure conditions of their formation. P11: Use of photomicrographs to identify minerals and rock textures of metamorphic rocks to identify rock type and to deduce the temperature and pressure conditions of their formation. Identification in hand specimen of the following metamorphic rocks from their composition, texture and other diagnostic features: marble, metaquartzite, spotted rock, hornfels, slate, schist, gneiss. For exemplification of mathematical skills see Mathematical Guidance for AS Geology. The mathematical skills identified are not exclusive to this section of the specification. Candidates should be aware of the metamorphic changes in chemically varied clay-rich rocks (e.g. shale) compared to those dominated by quartz and calcite (sandstones and limestone). Candidates need only have knowledge of the metamorphic rocks indicated. Candidates should be able to identify the stated metamorphic rocks in hand specimen and the field. It is understood that it might not be possible to investigate the full range of rocks in the field or that this list is exclusive.
Topic 3: TIME AND CHANGE Key Idea 2:Geological events can be placed in relative and absolute time scales Knowledge and understanding Geological techniques and skills Comments a. Geological events can be placed in relative time scales using criteria of relative age: evolutionary change in fossils, superposition of strata, unconformities, cross- cutting relationships, included fragments,‘way- up’ criteria. Interpretation of age relations of rocks and rock sequences using maps, cross-sections and in the field. P18: The application of one or more criteria of relative age (evolutionary change in fossils, superposition of strata, unconformities, cross-cutting relationships, included fragments, 'way-up criteria') in the field to place geological events in relative time sequences. b. Some rocks and minerals can be dated radiometrically to give an absolute age. This involves radioactive decay and the principles of radiometric dating; radioactive series and radioactive half-life; radiometric dating as exemplified by Potassium – Argon (40K– 40Ar), Samarium – Neodymium (147Sm –143Nd). Simple use of the principles of radiometric dating (decay rates and the half-life concept) to calculate the absolute age of a sample. Evaluation of the assumptions, accuracy and limitations inherent in the radiometric dating method. Candidates will need to know that differences between the K – Ar and Sm – Nd methods and understand the principle of using the gradient of an isochron to establish relative age in the latter. Candidates will not be expected to plot isochrons or calculate age from isochrons but simply interpret relative age. c. Fossils are used in relative dating. Observation and identification of appropriate morphological features and their changes through time: graptolites – number and position of stipes, thecal shape in the Early Palaeozoic. cephalopods – suture lines in the Late Palaeozoic and Mesozoic (goniatite, ceratite and ammonite). Candidates are expected to be able to provide a relative date to a formation based on graptolite or cephalopod assemblages within the appropriate time frame (Early Palaeozoic and Mesozoic).
Topic 4: EARTH STRUCTURE AND GLOBAL TECTONICS Key Idea 1: The Earth has a concentrically zoned structure and composition Knowledge and understanding Geological techniques and skills Comments a. The Earth has a layered structure: crust, mantle, outer and inner core. Each layer has a distinctive composition and/or rheological properties. Direct and indirect evidence is derived from meteorite (stony, iron) compositions, mantle xenoliths, mean density calculations and geophysical measurements (seismology, geomagnetism, gravity, conductivity). Analysis of seismological evidence for the internal structure of Earth: P and S body waves, surface waves, time- distance curves, shadow zones, velocity-depth models of Earth structure, density distribution with depth. Translation of information between graphical, numerical and algebraic forms. P19: Measurement of the densities of representative samples of Earth layers (e.g. granite, basalt). Simple analysis of geomagnetic evidence for core composition and processes. Candidates should be able to use evidence to interpret the state, depth and probable composition of the Earth’s layers. For exemplification of mathematical skills see Mathematical Guidance for AS Geology. The mathematical skills identified are not exclusive to this section of the specification. b. The crust is a thin layer of distinctive composition overlying the mantle; continental and oceanic crust can be recognised and distinguished by their differing thicknesses, composition and structure. Interpretation of geophysical data on crustal structure (seismic, gravity, magnetic) from continental and oceanic areas. Analysis of ocean drilling data to re-interpret the Mohorovičić discontinuity (Moho) at the base of the crust (e.g. Joides Resolution 360). Candidates should be given the opportunity to evaluate and validate the new knowledge obtained from current ongoing scientific research. the significance of serpentinite at the Moho discontinuity
Specification reference: 1.1e Aim: To use physical and chemical testing to identify minerals. Apparatus: Mineral testing equipment: Streak plate/unglazed tile to test the colour of powdered minerals. Dilute hydrochloric acid (“bench strength” 0.5 mol dm−3) in a dropper bottle to test if a mineral is a carbonate. Copper coin (pre 1992 coins are 97% copper, post 1992 they are copper plated steel), hardness ~3.5 on Mohs’ scale. Steel pin/needle (dissecting pin from Biology department or steel nail), hardness ~5.5 on Mohs’ scale. Learners to also use own fingernail, hardness ~2.5 on Mohs’ scale. Method: Carry out the appropriate tests and record results. Complete a table (similar to below) to logically record the results of observations. Description and identification of mineral specimen X Colour Crystal shape Cleavage Fracture Hardness mineral is scratched by mineral is softer than mineral is not scratched by mineral is harder than hardness of mineral is between and on Mohs hardness scale Density Streak Lustre Reaction with cold dilute HCl Conclusion: identification of mineral X