BGCSE Geography (Botswana Senior Secondary Education BSSE) cheat sheet

Earth's layers by depth: crust (0-~70 km), mantle (~70-2,900 km), outer core (2,900-5,150 km, liquid), inner core (5,150-6,371 km, solid iron-nickel).

Continental crust is granitic, thick (30-70 km) and less dense (~2.7 g/cm3); oceanic crust is basaltic, thin (5-10 km) and denser (~3.0 g/cm3).

The lithosphere = crust + rigid upper mantle; it is broken into plates and floats on the weaker asthenosphere.

The Mohorovicic discontinuity (Moho) marks the boundary between crust and mantle; the Gutenberg discontinuity separates mantle from core.

Isostasy: lighter/thicker crust rides higher; loading (ice, sediment) causes subsidence, unloading causes uplift.

Earth's magnetic field is generated by convection of liquid iron in the outer core (geodynamo).

Seismic P-waves travel through solids and liquids; S-waves cannot pass liquids, which proves the outer core is liquid.

Rock types: igneous (cooled magma/lava), sedimentary (deposited layers, may contain fossils), metamorphic (heat/pressure altered).

Convergent boundaries: oceanic-continental gives subduction, deep trenches and volcanic mountain arcs; continental-continental gives fold mountains (e.g., Himalayas).

Divergent boundaries create mid-ocean ridges, rift valleys and new crust; sea-floor spreading rate is typically 2-10 cm per year.

Transform (conservative) boundaries slide past each other, producing shallow earthquakes but little volcanism (e.g., San Andreas Fault).

Hotspots form volcanic island chains as a plate moves over a fixed mantle plume (e.g., Hawaii, Galapagos).

Earthquake focus = point of rupture underground; epicentre = point on the surface directly above it.

Richter scale is logarithmic: magnitude 6 releases about 32 times the energy of magnitude 5.

Fold mountains form where compressional forces buckle strata; fault-block mountains form where blocks are uplifted or dropped between faults.

Volcanic landforms: shield volcanoes from fluid basaltic lava (gentle slopes); composite cones from alternating ash and viscous lava (steep).

Atmosphere composition: ~78% nitrogen, ~21% oxygen, ~0.9% argon, ~0.04% carbon dioxide, plus variable water vapour.

Troposphere (0-~12 km) holds most water vapour and weather; temperature falls about 6.5 degrees C per km (lapse rate).

Air pressure falls with altitude; isobars close together indicate steep pressure gradient and strong winds.

Wind blows from high to low pressure, deflected right in the Northern Hemisphere (Coriolis effect).

Relative humidity = (actual vapour content / saturation capacity) x 100; dew point is the temperature at which air becomes saturated.

Convectional rain: surface heating causes rising air, cooling, condensation and heavy afternoon showers; relief rain falls on windward slopes.

Climate controls: latitude, altitude, distance from sea, ocean currents, prevailing winds and aspect.

Tropical marine climate (Bahamas/Caribbean): small annual temperature range (~5-8 degrees C), high humidity, wet season May-November.

Flows: evaporation, transpiration, condensation, precipitation, interception, infiltration, percolation, surface runoff, groundwater flow.

Stores: oceans (~97% of water), ice caps and glaciers (~2%), groundwater, lakes, rivers, atmosphere (tiny but fast-cycling).

Only about 2.5% of Earth's water is fresh, and most of that is locked in ice or deep groundwater.

The water balance: precipitation = evapotranspiration + runoff + change in storage.

Deforestation reduces interception and infiltration, raising surface runoff and flood risk.

Urbanisation with impermeable surfaces increases runoff and reduces infiltration and groundwater recharge.

A drainage basin is the area drained by a river and its tributaries, bounded by a watershed (interfluve).

Groundwater flows through permeable rock (aquifers); impermeable rock (aquiclude) blocks it and can create springs.

Erosion processes: hydraulic action, abrasion (corrasion), attrition and solution (corrosion).

Transport processes: traction (rolling), saltation (bouncing), suspension and solution.

Long profile: steep upper course with vertical erosion, gentler middle course with lateral erosion, flat lower course with deposition.

V-shaped valleys form by vertical erosion in the upper course; meanders and oxbow lakes form by lateral erosion and deposition in the lower course.

A waterfall forms where a band of resistant rock overlies softer rock; a plunge pool is excavated by hydraulic action and abrasion.

Discharge = cross-sectional area x mean velocity (Q = A x V), measured in cubic metres per second (cumecs).

Storm hydrograph: lag time shortens and peak discharge rises with impermeable rock, steep slopes, urbanisation or saturated soil.

Deposition occurs where velocity falls: inside meander bends (point bars), at the river mouth (delta) and where the gradient flattens.

Waves are formed by wind; wave height depends on wind speed, duration and fetch (distance of open water).

Constructive waves: low frequency, long wavelength, strong swash, weak backwash, build beaches. Destructive waves: high frequency, short wavelength, strong backwash, erode.

Erosion processes: hydraulic action, corrasion, attrition, solution and wave quarrying.

Longshore drift moves sediment along the coast in the direction of the dominant wave approach.

Coastal landforms: headlands and bays (differential erosion), cliffs, wave-cut platforms, caves-arches-stacks, spits and bars (deposition).

Coral reefs grow in warm (20-30 degrees C), shallow, clear, salty water; they fringe Caribbean islands and protect coasts from wave energy.

Sea-level rise from thermal expansion and melting ice increases coastal erosion, saltwater intrusion and flooding risk on low islands.

Tides are caused mainly by the gravitational pull of the Moon and Sun; spring tides occur at new and full moon, neap tides at quarter moons.

Ecosystem = community of organisms interacting with each other and their physical environment.

Food chains transfer energy; only about 10% passes to the next trophic level, so food chains rarely exceed 4-5 links.

Producers (plants) capture energy by photosynthesis; decomposers recycle nutrients back into the soil.

Tropical rainforest: high rainfall (over 2,000 mm/yr), high biodiversity, layered canopy, nutrient-poor soils because nutrients are in biomass.

Mangroves and seagrass beds are nursery habitats and coastal buffers in the Bahamas and Caribbean; coral reefs are highly productive but fragile.

Nutrient cycling is rapid in tropical ecosystems; removal of vegetation quickly depletes soil fertility.

Biodiversity hotspots are areas of high species richness under threat; invasive species (e.g., lionfish) disrupt reef food webs.

Adaptations: xerophytes reduce water loss; halophytes tolerate salt; epiphytes gain light in the canopy.

Natural increase = birth rate minus death rate (per 1,000); migration change = immigration minus emigration.

Population growth rate = natural increase + net migration, expressed as a percentage per year.

Doubling time (years) is approximately 70 divided by the annual growth rate in percent.

Population density = total population / total area (persons per square kilometre).

Demographic transition stages: high stationary, early expanding, late expanding, low stationary, declining.

Population pyramids: broad base indicates high birth rates and youthful population; narrow base indicates ageing population.

Settlement sites: wet-point (water), defensive (hilltop), bridging point, route centre, fertile plain, sheltered harbour.

Rural-urban migration is pushed by low rural incomes and pulled by jobs, education and services in cities.

Sectors: primary (extraction), secondary (manufacturing), tertiary (services), quaternary (knowledge/research).

Clark-Fisher model: as economies develop, employment shifts from primary to secondary to tertiary.

Factors of industrial location: raw materials, power, transport, labour, market, capital and government policy.

Multiplier effect: new industry creates jobs and income, which generates further demand and employment locally.

Bahamas economy is dominated by tourism and financial services; agriculture and manufacturing are small contributors.

Caribbean economies are vulnerable to external shocks (hurricanes, tourism downturns) because of narrow export bases.

Value added = output value minus cost of inputs; higher value-added activities generate more income per worker.

Informal sector activity is not taxed or recorded, so it is often missing from official employment statistics.

Subsistence farming produces mainly for the farmer's family; commercial farming is for sale and profit.

Intensive farming uses high inputs (labour, capital, fertiliser) on small areas; extensive farming uses low inputs on large areas.

Shifting cultivation: land cleared and farmed briefly, then abandoned to allow fertility recovery.

Green Revolution: high-yield varieties, irrigation and fertiliser raised yields but increased costs and inequality.

Tourism types: mass, eco, cultural, adventure; tourism brings foreign exchange but can cause leakage and environmental pressure.

Caribbean tourism depends on climate, beaches, cruise ship arrivals and air links; hurricane season (June-November) disrupts demand.

Industrial pollution controls: scrubbers, waste treatment, zoning industry away from housing, and emission limits.

Sustainable agriculture: crop rotation, terracing, drip irrigation and organic matter return reduce soil degradation.

The Bahamas is an archipelago of about 700 islands and cays on a limestone platform, with a tropical marine climate.

The Bahamas lies in the Atlantic, outside the main Caribbean island chain, but is a CARICOM member.

Hurricanes form over warm ocean water (over 26.5 degrees C) between 5 and 20 degrees latitude and track westward, then recurve.

Hurricane hazards: storm surge, high winds, flooding, coastal erosion and landslides on steep Caribbean islands.

The Caribbean plate boundary near the Lesser Antilles produces volcanic eruptions and earthquakes (e.g., Montserrat, Haiti 2010).

Preparedness measures: early warning, building codes, evacuation plans, storm shelters and coastal mangrove protection.

Economic vulnerability: small size, narrow export base, dependence on tourism and remittances, high import costs.

Caribbean climate is influenced by the trade winds (northeast), the North Atlantic subtropical high and the ITCZ.

Scale: 1:50,000 means 1 cm on the map = 50,000 cm (500 m) on the ground.

Grid references: four-figure gives a square (eastings then northings); six-figure gives a point within the square.

Contour lines join points of equal height; closely spaced contours indicate steep slopes, widely spaced contours gentle slopes.

Cross-sections are drawn by transferring contour heights along a line and plotting height against distance.

Bearing is measured clockwise from north in degrees; a back bearing differs by 180 degrees.

Mean, median and mode summarise data; a scatter graph shows correlation between two variables.

Fieldwork sequence: aim, hypothesis, sampling method, data collection, presentation (graphs/maps), analysis and evaluation.

Sampling types: random (unbiased), systematic (regular interval, e.g., every 10 m) and stratified (by subgroup).