Every Earth Science concept in the high school Science Bowl study set (grades 9-12), with a short definition for each. Read through them here, then drill them as flashcards or practise real Earth Science questions.
Earth's lithosphere divided into plates driven by mantle convection. Convergent boundaries: subduction (oceanic under continental → volcanoes/trenches) or continent–continent collision (mountains). Divergent: plates separate (mid-ocean ridges). Transform: plates slide past (strike-slip faults, earthquakes).
Igneous rocks: cooled magma/lava; intrusive (slow cooling, large crystals) = granite; extrusive (fast) = basalt. Sedimentary: compacted sediments (limestone, sandstone, shale). Metamorphic: heat + pressure transform existing rock (marble from limestone; quartzite from sandstone). All types can convert to others.
Troposphere (0–12 km): weather; T decreases with altitude. Stratosphere (12–50 km): ozone layer; T increases. Mesosphere (50–80 km): coldest; meteors burn. Thermosphere: aurora borealis; ionosphere. Exosphere: outermost; merges with space. Tropopause/stratopause mark boundaries.
Crust: oceanic (denser basaltic) and continental (granitic). Mantle (largest): silicate rock; partially molten asthenosphere allows plate movement. Outer core: liquid iron-nickel; convection generates Earth's magnetic field via dynamo effect. Inner core: solid iron-nickel despite high temperature (extreme pressure).
Eons: Hadean, Archean, Proterozoic, Phanerozoic. Phanerozoic eras: Paleozoic (invertebrates, fish, amphibians), Mesozoic (Triassic/Jurassic/Cretaceous; dinosaurs, first mammals), Cenozoic (Paleogene/Neogene/Quaternary; mammals dominant, humans). Radiometric dating uses radioactive decay half-lives.
Evaporation + transpiration (evapotranspiration) move water into atmosphere. Condensation forms clouds. Precipitation returns water to surface. Infiltration recharges groundwater. Surface runoff flows to rivers and oceans. Solar energy drives the cycle; gravity pulls water downward.
Naturally occurring, inorganic, crystalline solids with definite chemical composition. Identified by hardness (Mohs scale: talc=1, gypsum=2, calcite=3, fluorite=4, apatite=5, feldspar=6, quartz=7, topaz=8, corundum=9, diamond=10), luster, streak, cleavage/fracture, and specific gravity.
P-waves (primary, compressional): fastest; travel through solids and liquids. S-waves (shear): solids only; used to identify liquid outer core. Surface waves cause most structural damage. Hypocenter: underground origin. Epicenter: surface point above focus. Richter and moment magnitude scales measure size.
Surface currents driven by wind; gyres rotate clockwise in NH, counterclockwise in SH (Coriolis effect). Thermohaline circulation: deep ocean conveyor belt driven by density differences (cold, salty water sinks). Upwelling brings cold, nutrient-rich deep water to surface, supporting marine ecosystems.
High pressure (anticyclone): sinking air, clear skies. Low pressure (cyclone): rising air, clouds and precipitation. Cold front: dense cold air pushes warm air up rapidly (thunderstorms). Warm front: warm air rises gradually over cold (steady rain). Coriolis deflects winds; jet streams steer weather systems.
Shield volcanoes: broad, gently sloping; basaltic lava flows; low viscosity (e.g., Hawaiian). Composite/stratovolcanoes: steep, explosive; andesitic/rhyolitic magma; high viscosity (e.g., Mt. St. Helens). Cinder cone: steep, pyroclastic material. Hotspot volcanism: mantle plumes not at plate boundaries.
Glaciers form where snowfall exceeds melting; compressed snow becomes ice. Continental glaciers (ice sheets) covered much of North America during Pleistocene ice ages. Valley glaciers carve U-shaped valleys, cirques, horns, and fjords. Glacial till is unsorted sediment deposited by ice.
Mechanical weathering: breaks rock without changing composition (freeze-thaw, abrasion). Chemical weathering: alters minerals (oxidation, hydrolysis, carbonation — CO₂ + H₂O → carbonic acid dissolves limestone). Erosion: transport of weathered material by water, wind, ice, or gravity. Soil forms from weathered rock + organic matter.
Caused by gravitational pull of the Moon (primary) and Sun. High tide on the side facing the Moon and on the opposite side (inertia). Spring tides (highest range): Moon, Earth, and Sun aligned (new/full moon). Neap tides (lowest range): Moon and Sun at 90° (quarter moons).
Inner rocky planets: Mercury, Venus, Earth, Mars. Outer gas giants: Jupiter, Saturn. Ice giants: Uranus, Neptune. Asteroid belt between Mars and Jupiter. Kuiper Belt beyond Neptune (contains Pluto). Oort Cloud: distant source of comets. Comets: icy bodies with tails pointing away from the Sun.
Stars form in nebulae via gravitational collapse. Main sequence: hydrogen fusion in core. H-R diagram: luminosity vs temperature; main sequence is diagonal band. After H is exhausted: expands to red giant. Low-mass stars → white dwarf. High-mass stars → supernova → neutron star or black hole.
Milky Way: barred spiral galaxy; Sun is ~26,000 ly from center. Galaxy types: spiral, elliptical, irregular. Hubble's Law: v = H₀d (galaxies recede proportional to distance). Big Bang: universe ≈ 13.8 billion years old; supported by cosmic microwave background radiation and element abundances.
Fossils form when organisms are buried in sediment and minerals replace organic material. Index fossils: widespread, short time span; used for correlation and dating. Relative dating: using rock layers (stratigraphy); law of superposition: lower layers are older. Absolute dating uses radioactive isotopes (C-14, U-238).
Carbon moves between atmosphere (CO₂), biosphere (photosynthesis/respiration), hydrosphere (dissolved CO₂), and lithosphere (fossil fuels, limestone). Photosynthesis removes CO₂; respiration and combustion release it. Ocean is a major carbon sink. Human burning of fossil fuels increases atmospheric CO₂.
El Niño (ENSO warm phase): weakening of trade winds causes warm Pacific water to spread east → increased rainfall in South America, droughts in Australia/SE Asia. La Niña (cool phase): stronger trade winds → cooler eastern Pacific. Affects global weather patterns every 2–7 years.
Clouds form when moist air rises and cools to the dew point, condensing around condensation nuclei. Types: cirrus (high, wispy), stratus (low, layered, fog), cumulus (puffy, fair weather), cumulonimbus (thunderstorm). Precipitation types: rain, snow, sleet, hail. Orographic lift: mountains force air upward.
Water stored in aquifers (permeable rock layers). Water table: upper surface of saturated zone. Recharge occurs where precipitation infiltrates permeable surface. Artesian wells: water under pressure; rises without pumping. Karst topography forms from dissolution of limestone by slightly acidic groundwater (sinkholes, caves).
The Moon orbits Earth in ~29.5 days (synodic period). Phases depend on the angle between the Moon, Earth, and Sun. New moon → waxing crescent → first quarter → waxing gibbous → full moon → waning gibbous → third quarter → waning crescent. Lunar eclipses: Earth's shadow on Moon (full moon). Solar eclipses: Moon between Earth and Sun (new moon).
Generated by convection currents in the liquid outer core (geodynamo). Magnetic poles are not aligned with geographic poles (magnetic declination). Magnetosphere deflects solar wind (charged particles); protects life from radiation. Magnetic pole reversals are recorded in oceanic crust — evidence for seafloor spreading.
Biomes are large regions defined by climate and dominant vegetation. Tropical rainforest (high T, high rainfall), savanna (wet/dry seasons), desert (low rainfall, hot or cold), temperate forest (seasonal), taiga/boreal forest (cold, conifers), tundra (permafrost, treeless). Determined by latitude, altitude, and ocean currents.
New oceanic crust forms at mid-ocean ridges as magma rises and solidifies. Crust moves away from ridge, becomes older and denser, and eventually subducts at ocean trenches. Magnetic striping in oceanic crust records polarity reversals, providing key evidence. Explains why ocean floor is younger than continental crust.
Soil forms from weathered parent rock + organic matter (humus) over thousands of years. Soil horizons: O (organic litter), A (topsoil, humus-rich), B (subsoil, leached minerals accumulate), C (partially weathered parent rock), R (bedrock). Soil texture: sand (coarse), silt (medium), clay (fine, holds water and nutrients). Loam (mixture of all three) is best for agriculture. Soil pH affects nutrient availability. Erosion and compaction degrade soil quality.
Wind-driven surface waves: energy travels through water, not water itself; circular orbital motion of water decreases with depth. Wave height, period, and wavelength determined by wind speed, fetch, and duration. Tsunamis: generated by submarine earthquakes, landslides, or volcanic eruptions; long wavelength (~200 km), low amplitude in deep ocean, but slow and tall near shore (shoaling). Travel at speeds up to 800 km/h; warning systems detect via ocean buoys.
Key evidence: rising global average temperatures (+1.1°C since pre-industrial); declining Arctic sea ice and glacial retreat; rising sea levels (thermal expansion + ice melt, ~3.6 mm/yr); ocean acidification (CO₂ + H₂O → H₂CO₃); shifting species ranges; earlier spring phenology. Ice cores from Greenland/Antarctica provide 800,000-year records of CO₂ and temperature. Attribution studies link warming to human GHG emissions (95%+ scientific consensus).
Long-term periodic variations in Earth's orbit and orientation that drive ice ages. Eccentricity (~100,000 yr cycle): changes in orbital ellipticity. Axial tilt/obliquity (~41,000 yr): tilt varies from 22.1° to 24.5°; greater tilt → more extreme seasons. Precession (~26,000 yr): wobble of Earth's rotation axis like a spinning top. Combinations of cycles control when ice sheets advance and retreat. Glacial-interglacial cycles correspond to Milankovitch periods confirmed by ocean sediment cores.
Ozone (O₃) in the stratosphere (15–35 km) absorbs harmful UV-B and UV-C radiation. Formation: O₂ + UV → 2O; O + O₂ → O₃. Depletion: chlorofluorocarbons (CFCs) release Cl radicals in stratosphere; Cl + O₃ → ClO + O₂ (catalytic destruction). Antarctic ozone hole forms each spring (polar stratospheric clouds + sunlight). Montreal Protocol (1987) phased out CFCs; ozone is slowly recovering. UV-B damage: skin cancer, cataracts, ecosystem harm.
Drainage basin (watershed): land area draining to a single river system. Stream discharge Q = A × v (cross-sectional area × velocity). Erosion: faster water in outer bends; deposition in inner bends → meanders develop. Oxbow lakes form when meanders are cut off. Floodplains: flat fertile areas beside rivers built by sediment deposition. Alluvial fans: fan-shaped deposits where streams enter flat areas. Deltas form where rivers slow and deposit sediment into standing water.
Downslope movement of rock, soil, and debris under gravity. Types by speed and water content: creep (slow, imperceptible soil movement), earthflow (saturated soil, slow), mudflow/lahar (volcanic mudflow; fast, fluid), debris avalanche (dry, rapid), rockslide/rockfall (sudden failure of bedrock). Triggers: heavy rainfall, earthquakes, undercutting, removal of vegetation, freeze-thaw. Angle of repose: maximum slope angle at which unconsolidated material is stable (~34° for dry sand).
Hadley cells: tropical convection cells where warm air rises at equator (ITCZ), spreads poleward, cools, and sinks at ~30° latitude → subtropical deserts. Ferrel cells: mid-latitudes (30°–60°), surface winds blow poleward. Polar cells: cold air sinks at poles, flows toward 60°. Trade winds: surface winds in Hadley cells blow toward equator (easterlies). Westerlies: dominant mid-latitude surface winds. Jet streams: fast upper-level winds at boundaries between cells.
Principle that Earth's crust floats in gravitational equilibrium on the denser mantle (like an iceberg in water). Thick continental crust has a deep 'root' extending into mantle; mountains have deeper roots. Glacial isostatic rebound: land rises after removal of glacier weight (Scandinavia is still rising ~1 cm/yr since last ice age). Isostatic adjustment occurs because mantle behaves like a viscous fluid on long timescales.
Apparent deflection of moving objects on a rotating Earth. In Northern Hemisphere: objects deflect to the right. In Southern Hemisphere: to the left. Caused by the difference in rotational speed at different latitudes. Affects: wind patterns (cyclones rotate counterclockwise in NH, clockwise in SH), ocean gyres, long-range projectiles, atmospheric jets. Does NOT significantly affect bathtub drains (too small scale). Coriolis acceleration: a = 2v × Ω.
Remote sensing: gathering information about Earth's surface from a distance (satellites, aircraft). Passive sensors detect reflected sunlight (multispectral, hyperspectral imagery). Active sensors emit their own energy: radar (uses microwave pulses; works through clouds), LiDAR (laser pulses; measures elevation precisely). GPS: 24+ satellites; receiver calculates position from time delays of signals from ≥4 satellites; accuracy to meters or centimeters (differential GPS).
Theory of solar system formation: a rotating cloud (nebula) of gas and dust collapsed under gravity ~4.6 billion years ago. Conservation of angular momentum caused it to spin faster and flatten into a protoplanetary disk. Center accreted into the proto-Sun; heat ignited nuclear fusion. Rocky planets formed close to the Sun (high temperatures prevented gas/ice retention); gas giants formed farther out (abundant volatiles). Planetesimals grew by accretion; impacts during Late Heavy Bombardment (~3.8 Ga) shaped inner solar system.
Acid rain: precipitation with pH < 5.6 due to SO₂ (from burning sulfur-rich coal, volcanoes) and NOₓ (combustion, lightning) reacting with water to form H₂SO₄ and HNO₃. Effects: acidifies lakes (harms aquatic life), leaches nutrients from soil, corrodes stone and metals. Smog: photochemical (NOₓ + VOCs + UV → ozone at ground level) or industrial (SO₂ + particulates). Clean Air Act (US) reduced acid rain by scrubbing SO₂ from power plant emissions.
Protostar → main sequence (hydrogen fusion, stable). Low/medium mass (like Sun): main sequence → red giant (H shell burning, He core) → planetary nebula → white dwarf (electron degeneracy pressure). High mass stars: main sequence → red supergiant → Type II supernova → neutron star (pulsar if rotating) or black hole (if >3 solar masses). H-R diagram: luminosity vs. surface temperature; main sequence is diagonal band; giants upper right; white dwarfs lower left.