Earth and Basic Facts
The Earth and Basic Facts domain tests the physical foundations the rest of geography rests on: Earth's shape and motions, the latitude-longitude grid, plate tectonics and landforms, the atmosphere and climate, soils and vegetation, and water. Questions tend to ask for definitions, cause-and-effect, and simple calculations.
Earth's shape, motions, and grid
Earth is an oblate spheroid: equatorial diameter about 12,756 km, polar about 12,714 km. Its axis tilts 23.5 degrees from perpendicular to the orbital plane, so the subsolar point migrates between 23.5 N and 23.5 S. Rotation is west to east and takes 24 hours; revolution takes about 365.24 days. Equinoxes occur when the subsolar point is on the equator; solstices when it reaches a tropic. Latitude lines are parallels measured 0 to 90 degrees north or south; longitude lines are meridians measured 0 to 180 degrees east or west from Greenwich. One degree of latitude is about 111 km everywhere; one degree of longitude shrinks from about 111 km at the equator to zero at the poles.
Physiography
Plate tectonics explains major landforms. Divergent boundaries create rifts and mid-ocean ridges; convergent boundaries produce subduction zones, trenches, island arcs, and fold mountains; transform boundaries produce faults such as the San Andreas. The Ring of Fire surrounds the Pacific.
Atmosphere, climate, soils, vegetation
Insolation drives global circulation: Hadley cells near the equator, Ferrel cells at mid-latitudes, and polar cells. The Coriolis effect deflects winds right in the Northern Hemisphere and left in the Southern. Orographic lifting and rain shadows explain wet windward and dry leeward slopes. Koppen classification groups climates by temperature and precipitation. Soils reflect climate, parent material, organisms, relief, and time; leaching dominates humid climates and salinization arid ones. Biomes grade from tropical rainforest through savanna, desert, grassland, temperate forest, taiga, and tundra.
Water
The hydrologic cycle moves water through evaporation, transpiration, condensation, precipitation, runoff, and infiltration. An aquifer is permeable rock storing groundwater; a watershed is the area draining to a common outlet.
Worked example
A place at 30 N receives noon sun on the June solstice. The subsolar point is 23.5 N. Solar angle = 90 minus (30 minus 23.5) = 83.5 degrees. Reasoning: the angle equals 90 degrees minus the latitude difference between observer and subsolar point.
Traps
- Confusing latitude, which uses parallels, with longitude, which uses meridians.
- Thinking the equinox has the greatest day-length difference; it has equal day and night.
- Reversing Coriolis deflection between hemispheres.
- Assuming one degree of longitude is always 111 km.