Geology, the atmosphere, oceans, and the climate system.
A study reference, not a substitute for primary sources.
Updated 2026-06-02.
Structure of the Earth
Crust — outermost layer; continental crust is thicker (~30–50 km) and less dense (granite-rich, felsic); oceanic crust is thinner (~5–10 km) and denser (basalt-rich, mafic).
Moho (Mohorovičić discontinuity) — boundary between crust and mantle; discovered by seismic velocity changes (Andrija Mohorovičić, 1909).
Mantle — ~2,900 km thick; mostly solid silicate rock but flows plastically over geologic timescales. The asthenosphere (upper mantle, ~100–350 km) is partially molten and allows plate movement.
Outer core — liquid iron-nickel; its convection generates Earth’s magnetic field via the geodynamo.
Inner core — solid iron-nickel despite temperatures of ~5,000–6,000 °C; extreme pressure keeps it solid; radius ~1,220 km.
Seismic waves — P-waves (primary, compressional, travel through solids and liquids); S-waves (secondary, shear, travel only through solids). The liquid outer core blocks S-waves, revealing its liquid state.
Shadow zone — region ~103°–142° from an earthquake epicenter that receives no direct S- or P-waves, indicating the liquid outer core.
Gutenberg discontinuity — boundary between the mantle and the outer core at ~2,900 km depth; named for seismologist Beno Gutenberg, who identified it from P-wave travel-time data in 1914; marks the transition from solid silicate mantle to liquid iron-nickel outer core.
Love waves — surface seismic waves that move the ground horizontally perpendicular to the direction of wave propagation; they are faster than Rayleigh waves and cause significant lateral shaking damage.
Rayleigh waves — surface seismic waves that roll the ground in an elliptical retrograde motion (like ocean waves); slower than body waves; responsible for much of the shaking felt during earthquakes.
Inge Lehmann — Danish seismologist (1888–1993) who discovered Earth’s solid inner core in 1936 by analyzing anomalous P-wave arrivals in the shadow zone; her paper “P′” is among the most important in geophysics.
Plate Tectonics
Theory — Earth’s lithosphere (crust + rigid upper mantle) is divided into ~15 major tectonic plates that move over the asthenosphere; formalized in the 1960s, building on Alfred Wegener’s continental drift hypothesis (1912).
Driving mechanisms — ridge push (new oceanic crust pushes plates apart at mid-ocean ridges) and slab pull (subducting dense oceanic crust drags plates); mantle convection plays a role.
Divergent boundaries — plates move apart; creates mid-ocean ridges (e.g., Mid-Atlantic Ridge) or continental rift valleys (e.g., East African Rift). New oceanic crust forms by seafloor spreading.
Convergent boundaries — plates move together; produces subduction zones (oceanic sinking beneath continental or oceanic crust, generating ocean trenches, volcanoes, and earthquakes) or collision zones (two continents: mountain building, e.g., Himalayas from India–Eurasia collision).
Transform boundaries — plates slide horizontally past each other; produces strike-slip faults (e.g., San Andreas Fault, California).
Pangaea — supercontinent that began breaking up ~175–200 Ma. Earlier supercontinents include Rodinia (~1.1 Ga) and Columbia/Nuna.
Paleomagnetism — alternating bands of normal and reversed magnetic polarity symmetrically flanking mid-ocean ridges provided key evidence for seafloor spreading (Vine-Matthews-Morley hypothesis, 1963).
Hot spots — mantle plumes stationary relative to plates; the Hawaiian Island chain formed as the Pacific Plate moved over the Hawaiian hot spot.
Hawaiian-Emperor seamount chain — the Hawaiian Islands grade northwest into a chain of progressively older seamounts that bends sharply northward at the Emperor chain (~47 Ma); the bend records a change in Pacific Plate motion direction; Kauai is older than Hawaii (the Big Island), which sits over the active hot spot.
Wadati-Benioff zone — the inclined plane of seismicity that defines a subducting oceanic plate as it descends into the mantle; earthquakes occur down to ~670 km; named independently by Japanese seismologist Kiyoo Wadati (1920s) and American seismologist Hugo Benioff (1950s).
Wilson cycle — the full life cycle of an ocean basin: continental rifting → new ocean forms → ocean widens → subduction begins → ocean narrows → continents collide → suture zone; named for J. Tuzo Wilson; explains why ancient orogenic belts contain ophiolites and blueschist.
Vine-Matthews-Morley hypothesis — the 1963 proposal by Frederick Vine, Drummond Matthews, and independently Lawrence Morley that symmetric magnetic-reversal stripes on the seafloor flanking mid-ocean ridges record seafloor spreading and geomagnetic reversals; provided the decisive evidence for plate tectonics.
Geomagnetic reversal — periodic swap of Earth’s magnetic north and south poles; recorded in the palaeomagnetic signature of cooling oceanic crust; the current normal polarity epoch (Brunhes chron) began ~780,000 years ago; reversals are recorded in the geomagnetic polarity time scale (GPTS).
Gondwana — the southern supercontinent that included South America, Africa, Antarctica, Australia, the Indian subcontinent, and the Arabian Peninsula; began to break up after Pangaea split (~180 Ma); named by Eduard Suess.
Laurasia — the northern supercontinent (North America, Europe, most of Asia) that formed when Pangaea split; separated from Gondwana by the Tethys Sea.
Rodinia — Precambrian supercontinent assembled ~1.1 Ga and rifted apart ~750–700 Ma; preceded Pangaea; its reconstruction is debated but Australia and Antarctica are placed near the core.
Seafloor spreading — the process by which new oceanic crust is created at mid-ocean ridges as magma wells up, cools, and spreads symmetrically outward; proposed by Harry Hess (~1960–1962); confirmed by palaeomagnetic stripes.
Major tectonic plates
Plate
Notes
Pacific
Largest; mostly oceanic; subducts under surrounding plates
North American
Includes most of North America and part of the North Atlantic
Eurasian
Colliding with Indian Plate (Himalayas)
Indian
Convergent with Eurasian; spreading at Carlsberg Ridge
Antarctic
Surrounds Antarctica; bounded mostly by divergent boundaries
African
Rifting along East African Rift
Nazca
Subducting under South American Plate (Andes)
Rocks and the Rock Cycle
Igneous rocks
Origin — solidification of magma (underground) or lava (surface).
Extrusive (volcanic) — cool quickly at the surface; fine-grained or glassy. Examples: basalt (most common volcanic rock; oceanic crust), obsidian (volcanic glass), pumice (vesicular, floats on water), rhyolite (felsic extrusive).
Felsic vs mafic — felsic rocks (granite, rhyolite) are silica-rich, lighter colored, lower density; mafic (basalt, gabbro) are magnesium/iron-rich, darker, denser.
Sedimentary rocks
Origin — compaction and cementation (lithification) of sediments, or precipitation from solution.
Clastic — fragments of other rocks: shale (clay-sized particles, most common sedimentary rock), sandstone (sand-sized), conglomerate (rounded gravel-sized clasts), breccia (angular clasts).
Chemical/biochemical — limestone (CaCO3, often from marine organisms; includes chalk and coquina); rock salt (halite, evaporite); chert (silica); coal (compressed organic matter).
Significance — fossils form almost exclusively in sedimentary rock; sedimentary layers (strata) record geologic history.
Metamorphic rocks
Origin — pre-existing rocks transformed by heat, pressure, or hydrothermal fluids without melting.
Contact metamorphism — heat from nearby magma intrusion. Regional metamorphism — large-scale heat and pressure, typically at convergent boundaries.
Metamorphic facies — sets of mineral assemblages that form under specific pressure-temperature conditions, regardless of rock composition; defined by indicator minerals: zeolite facies (low P-T), greenschist facies (chlorite, epidote), blueschist facies (high-P, low-T; subduction zones), amphibolite facies (staurolite, kyanite), granulite facies (high-T, lower-P), and eclogite facies (very high P; garnet + omphacite).
Index minerals — minerals used to track metamorphic grade in pelitic (shale-derived) rocks; in order of increasing temperature: chlorite → biotite → garnet → staurolite → kyanite → sillimanite (Barrow’s zones, Scottish Highlands).
Ophiolite — a sequence of ocean-floor rocks (deep-sea sediments, pillow basalts, sheeted dikes, gabbro, peridotite) thrust onto continental crust during collision; marks the suture of ancient oceans; classic examples in Oman (Semail) and Cyprus (Troodos).
The rock cycle
Cycle — igneous rock is weathered to sediment → lithification → sedimentary rock → metamorphism → metamorphic rock → melting → magma → igneous rock. Any rock type can transform to any other.
Weathering — mechanical (frost wedging, abrasion) breaks rock without changing composition; chemical (oxidation, hydrolysis, carbonation) alters mineral composition. Erosion transports weathered material.
Minerals and the Mohs Scale
Mineral definition — naturally occurring, inorganic, solid, with a definite chemical composition and crystalline structure.
Silicates — most abundant mineral group; built on SiO4 tetrahedra. Includes feldspar, quartz, mica, pyroxene, amphibole, olivine.
Feldspar — most abundant mineral in Earth’s crust; two main types: orthoclase (potassium feldspar) and plagioclase (sodium/calcium).
Quartz — SiO2; very common; hardness 7; varieties include amethyst, chert, flint.
Native elements — gold, silver, copper, sulfur, diamond (carbon), graphite (carbon, different polymorph).
Bowen’s reaction series — N.L. Bowen’s 1922 framework describing the sequence in which silicate minerals crystallize from a cooling basaltic magma; the discontinuous series (olivine → pyroxene → amphibole → biotite mica) and the continuous series (Ca-plagioclase → Na-plagioclase) both converge on orthoclase feldspar, muscovite mica, and quartz at the low-temperature end; explains the compositional diversity of igneous rocks.
Olivine — first mineral to crystallize in Bowen’s series; Mg2SiO4 to Fe2SiO4 solid solution; green, high density; dominant in the upper mantle; the gem variety is peridot.
Silicate structures — SiO4 tetrahedra linked in different arrangements: isolated (nesosilicates, e.g., olivine), single-chain (inosilicates, e.g., pyroxene), double-chain (amphibole), sheet (phyllosilicates, e.g., mica, clay), and framework (tectosilicates, e.g., quartz, feldspar); degree of polymerization increases viscosity in melts.
Mica group — sheet silicates with perfect basal cleavage; muscovite (white/colorless, K-Al mica) and biotite (black, K-Mg-Fe mica) are the main rock-forming varieties; forms under medium-grade metamorphism and in granitic rocks.
Pyroxene — single-chain inosilicate; important in mafic and ultramafic rocks; augite is the most common variety; orthopyroxene (enstatite-ferrosilite) and clinopyroxene families.
Amphibole — double-chain inosilicate; hornblende is the common dark rock-forming variety; distinguished from pyroxene by 60°/120° cleavage angles (vs. pyroxene’s ~90°) and hydroxyl content.
Mohs hardness scale
Hardness
Mineral
Common reference
1
Talc
Softest; feels soapy
2
Gypsum
Fingernail (~2.5)
3
Calcite
Copper coin (~3)
4
Fluorite
5
Apatite
Steel knife blade (~5.5)
6
Orthoclase feldspar
Steel file (~6.5)
7
Quartz
Scratches glass
8
Topaz
9
Corundum
Ruby and sapphire
10
Diamond
Hardest natural mineral
Other mineral properties — cleavage (flat breaking along planes), fracture (irregular breaking), luster (metallic, vitreous, resinous, pearly), streak (color of powdered mineral), specific gravity.
Ore minerals
Hematite — Fe2O3; primary ore of iron; red-brown streak; major constituent of banded iron formations.
Magnetite — Fe3O4; strongly magnetic iron ore; black, high density; also a minor constituent of many igneous rocks.
Bauxite — not a single mineral but a mixture of aluminum hydroxide minerals (gibbsite, boehmite, diaspore); the principal ore of aluminum; forms by intense tropical weathering.
Cassiterite — SnO2; principal ore of tin; very high specific gravity; historically mined in Cornwall and Southeast Asia.
Iron pyrite — FeS2; “fool’s gold”; brassy yellow, cubic crystals; not an iron ore of economic importance but widespread in sedimentary and hydrothermal settings.
Cinnabar — HgS; primary ore of mercury; bright red (“vermilion”); associated with volcanic and hydrothermal activity.
Galena — PbS; principal ore of lead (and a source of silver); very high specific gravity; perfect cubic cleavage; metallic luster.
Dolomite — CaMg(CO3)2; carbonate mineral (and rock name); not typically mined as a metal ore, but used as a refractory material, flux in steelmaking, and agricultural lime.
Geologic Time Scale
Eons — four: Hadean (formation of Earth ~4.6 Ga to 4.0 Ga), Archean (4.0–2.5 Ga; first life), Proterozoic (2.5 Ga–538 Ma; first eukaryotes, first multicellular life), Phanerozoic (538 Ma–present; complex animal life).
“Cambrian Explosion” — rapid diversification of animal body plans at the base of the Phanerozoic (~538 Ma).
Phanerozoic eras and periods (selected)
Era
Period
Ma (start)
Notes
Paleozoic
Cambrian
538
Explosion of animal phyla
Ordovician
485
Marine invertebrates; ends in mass extinction
Silurian
444
First vascular land plants
Devonian
419
“Age of Fishes”; first tetrapods
Carboniferous
359
Vast coal swamps; first reptiles
Permian
299
Ends in largest mass extinction (~96% species lost)
Mesozoic
Triassic
252
First dinosaurs and mammals
Jurassic
201
Dinosaurs dominate; first birds
Cretaceous
145
Flowering plants; ends with K-Pg extinction
Cenozoic
Paleogene
66
Mammals diversify
Neogene
23
Grasslands spread; hominids appear
Quaternary
2.6
Ice ages; Homo sapiens
Tertiary Period — informal/obsolete term for the interval now formally divided into the Paleogene (66–23 Ma) and Neogene (23–2.6 Ma); still encountered in older literature and some applied geology contexts.
Biostratigraphy — the use of fossil assemblages (index fossils) to correlate and date rock strata; developed systematically in the early 19th century by William Smith and Georges Cuvier; complements radiometric (absolute) dating.
Big Five mass extinctions — (1) Ordovician-Silurian (~444 Ma); (2) Late Devonian (~372 Ma); (3) Permian-Triassic (“The Great Dying,” ~252 Ma, ~90–96% species); (4) Triassic-Jurassic (~201 Ma); (5) Cretaceous-Paleogene (K-Pg, ~66 Ma, ~75% species, includes non-avian dinosaurs).
K-Pg extinction cause — Chicxulub impactor (Yucatán Peninsula, ~10 km asteroid) confirmed by iridium layer at the K-Pg boundary (Alvarez hypothesis); Deccan Traps flood volcanism contributed.
Burgess Shale — exceptionally preserved Cambrian Lagerstätte (~508 Ma) in British Columbia, Canada; discovered by Charles Walcott (1909); preserves soft-body anatomy of early animals including Anomalocaris, Opabinia, Hallucigenia, and Wiwaxia; reinterpreted by Harry Whittington, Simon Conway Morris, and Derek Briggs in the 1970s–1980s; central to debates over Cambrian diversity and Stephen Jay Gould’s Wonderful Life.
Cambrian explosion — rapid diversification of animal body plans beginning ~538 Ma, producing representatives of most modern animal phyla within a geologically brief span (~20 million years); causes debated (oxygen rise, ecological interactions, developmental toolkit evolution); also documented in Chengjiang biota (Yunnan, China, ~520 Ma).
Permian-Triassic extinction — the largest mass extinction (~252 Ma); killed ~90–96% of marine species and ~70% of terrestrial vertebrate species; nicknamed “The Great Dying”; likely caused by Siberian Traps volcanism (CO2, SO2 release), ocean anoxia, and global warming; recovery took ~5–10 million years.
Chicxulub crater — ~180 km diameter impact structure beneath the Yucatán Peninsula and Gulf of Mexico; formed ~66 Ma; confirmed as the K-Pg impactor by iridium anomaly, shocked quartz, and tektites; proposed by Luis and Walter Alvarez (1980); confirmed by drilling in the 1990s.
Radiometric dating — uses known decay rates of radioactive isotopes (e.g., U-238→Pb-206 for old rocks; K-40→Ar-40; C-14 for organic material up to ~50,000 years); provides absolute ages of rocks.
Law of superposition — in undisturbed strata, older layers lie below younger ones (Steno, 17th century).
Index fossils — fossils of organisms with wide geographic range and narrow time range, used to correlate and date rock layers.
Earthquakes and Volcanoes
Earthquakes
Cause — sudden release of elastic strain energy when rocks along a fault rupture and slip.
Focus (hypocenter) — the point underground where rupture begins. Epicenter — the point on the surface directly above the focus.
Richter scale — originally local magnitude (ML) based on maximum wave amplitude on a seismograph; logarithmic (each integer ~32x more energy). Saturates for great earthquakes (>~8).
Moment magnitude (Mw) — measures total energy released; does not saturate; the modern standard for large earthquakes. Numerically similar to Richter at moderate magnitudes.
Modified Mercalli scale — measures intensity (I–XII) based on felt effects and damage at a location, not energy released.
Ring of Fire — belt of frequent earthquakes and volcanoes around the Pacific basin, associated with subduction zones.
Seismograph / seismometer — instrument that records seismic waves; three stations needed to triangulate the epicenter.
Tsunami — ocean wave triggered by seafloor displacement (large undersea earthquake, submarine landslide, or volcanic eruption); wavelength hundreds of kilometers; devastating at shore.
Volcanoes
Shield volcano — broad, gently sloping; low-viscosity basaltic lava flows; e.g., Mauna Loa (Hawaii). Least explosive.
Composite volcano (stratovolcano) — steep, symmetrical; alternating lava and pyroclastic layers; high-viscosity silicic magma; e.g., Mount St. Helens, Fuji, Pinatubo. Most explosive.
Cinder cone — small, steep; built from pyroclastic fragments; e.g., Parícutin (Mexico, appeared 1943).
Caldera — large depression formed when a magma chamber empties and the overlying rock collapses; e.g., Yellowstone Caldera (supervolcano).
Pyroclastic flow — fast-moving current of hot gas and volcanic matter; the deadliest volcanic hazard; reached 700 °C+ (e.g., Vesuvius 79 CE, Mount Pelée 1902).
Volcanic explosivity index (VEI) — logarithmic scale 0–8 for eruption size; Pinatubo 1991 ≈ VEI 6, Toba ~74,000 BP ≈ VEI 8.
~75% of atmospheric mass; weather occurs here; temperature decreases with altitude
Stratosphere
12–50 km
Ozone layer (~15–35 km); temperature increases with altitude
Mesosphere
50–85 km
Coldest layer; meteors burn up here
Thermosphere
85–600 km
Very hot (absorbed UV/X-ray); aurora; ISS orbit
Exosphere
>600 km
Gradually merges with space
Composition — ~78% nitrogen (N2), ~21% oxygen (O2), ~0.93% argon (Ar), ~0.04% CO2, plus trace gases and variable water vapor.
Ozone layer — absorbs most UV-B and UV-C radiation; depletion caused by chlorofluorocarbons (CFCs); Montreal Protocol (1987) phased out CFCs; ozone hole over Antarctica is slowly recovering.
Tropopause / stratopause / mesopause — boundary layers between each atmospheric zone.
Ionosphere — the ionized upper portion of Earth’s atmosphere, roughly coinciding with the upper mesosphere and thermosphere (~60–1,000 km altitude); solar UV and X-ray radiation ionize gas molecules, creating free electrons and ions; divided into D layer (~60–90 km, daytime only), E layer (~90–150 km), and F layer (~150–600 km); critical for shortwave (HF) radio propagation — the ionosphere refracts radio waves back to Earth’s surface, enabling long-distance communication; disrupted by solar storms and geomagnetic disturbances; the ISS orbits within the ionosphere; causes GPS signal delays.
Lapse rate — rate of temperature decrease with altitude in the troposphere; dry adiabatic lapse rate ~10 °C/km; moist ~6 °C/km (latent heat released by condensation).
Weather and Climate
Atmospheric dynamics
Pressure systems — high pressure (anticyclone): air sinks, clear skies, winds rotate clockwise in the Northern Hemisphere. Low pressure (cyclone): air rises, clouds and precipitation, winds rotate counterclockwise in the Northern Hemisphere (reversed in Southern Hemisphere, Coriolis effect).
Coriolis effect — deflection of moving air (and water) due to Earth’s rotation; deflects right in the NH, left in the SH.
Trade winds — persistent winds blowing toward the equator from subtropical highs (~30°N/S), deflected westward by Coriolis; NE in NH, SE in SH.
Jet streams — fast, narrow air currents in the upper troposphere at ~30° and ~60° latitude; the polar jet stream steers mid-latitude weather systems; winds typically 120–250 km/h; exploited by transatlantic aviation (faster eastbound flights).
Föhn / Chinook winds — warm, dry downslope winds on the leeward side of mountains; air rises on the windward side losing moisture (and latent heat), then descends and compresses adiabatically, arriving warmer and drier than when it started; called Föhn in the Alps and Chinook in the Rocky Mountains; can rapidly melt snow (“snow eater”).
Orographic lift — forced ascent of air over a mountain range; causes adiabatic cooling, cloud formation, and precipitation on the windward side; rain shadow on the leeward side.
Cyclone vs. anticyclone — a cyclone is a low-pressure system with inward-spiraling winds (counterclockwise in NH); an anticyclone is a high-pressure system with outward-spiraling winds (clockwise in NH); the terms apply to mid-latitude systems as well as tropical cyclones (hurricanes/typhoons).
Hadley cell — equatorial air rises, moves poleward at altitude, sinks at ~30° latitude; drives tropics and subtropics. Ferrel cell (~30°–60°) and polar cell (>60°) complete the three-cell circulation model.
ITCZ (Intertropical Convergence Zone) — band of low pressure and heavy rainfall near the equator where NH and SH trade winds converge.
Fronts and precipitation
Cold front — cold air advancing under warm air; steep, produces cumulonimbus clouds and intense but brief precipitation.
Warm front — warm air advancing over cold air; gradual, produces stratus clouds and steady, prolonged precipitation.
Stationary / occluded fronts — stationary: front not moving; occluded: cold front catches a warm front, lifting the warm air.
Rain shadow — the dry leeward side of a mountain range; moist air rises and precipitates on the windward side, descends dry on the leeward side.
Types of precipitation — rain, snow, sleet (frozen rain), freezing rain (supercooled rain freezing on contact), hail (ice pellets grown in thunderstorm updrafts).
Climate classification
Köppen system — five main climate groups: A (tropical, hot and humid year-round), B (arid/semi-arid, deserts), C (temperate/humid mesothermal, e.g., Mediterranean, humid subtropical), D (continental/humid microthermal, cold winters), E (polar).
Mediterranean climate — dry summers, mild wet winters; “Csb/Csa” in Köppen; found on west coasts at ~30°–45° latitude.
Cloud types (Luke Howard classification) — cirrus (wispy ice-crystal clouds at high altitude, >6 km); cumulus (puffy, convective, fair-weather heaps); stratus (flat, layered, low-altitude); nimbus prefix or suffix (rain-bearing: nimbostratus, cumulonimbus); additional genera include altostratus, altocumulus, stratocumulus, cirrocumulus, cirrostratus; Luke Howard named them in 1803.
Cumulonimbus — the “king of clouds”; a tall, dense convective cloud extending from the lower troposphere to the tropopause (“anvil top”); produces thunderstorms, heavy rain, hail, lightning, and tornadoes.
Hurricane (tropical cyclone) — organized rotating tropical storm with sustained winds ≥119 km/h (74 mph); called hurricane in the Atlantic/E. Pacific, typhoon in the W. Pacific, cyclone in the Indian Ocean; powered by warm ocean water (≥26 °C) and release of latent heat; the eye is calm; the eyewall has the most intense winds; weakens rapidly over land or cool water.
Saffir-Simpson Hurricane Wind Scale — five-category scale for Atlantic/E. Pacific hurricanes based on maximum sustained wind speed: Cat 1 (119–153 km/h) through Cat 5 (≥252 km/h); does not rate storm surge or rainfall; developed by Herbert Saffir and Robert Simpson (~1971).
Enhanced Fujita (EF) scale — revised 2007 scale for tornado intensity based on damage indicators; EF0 (65–85 mph) through EF5 (>200 mph estimated); replaced the original Fujita scale (F-scale, devised by Tetsuya “Ted” Fujita); the strongest tornadoes (EF4–EF5) are responsible for ~70% of tornado fatalities.
Tornado formation — most tornadoes form from supercell thunderstorms with a rotating updraft (mesocyclone); wind shear changes wind speed and direction with height, creating horizontal vortices that are tilted vertical by the updraft; Tornado Alley (central US) is the most tornado-prone region globally.
Fog types — radiation fog (surface cools overnight by radiating heat, common in valleys); advection fog (warm moist air moves over a cold surface, e.g., San Francisco Bay); upslope fog (orographic); sea fog; evaporation/steam fog.
Monsoon — seasonal reversal of winds and associated heavy precipitation; most prominent in South Asia; driven by differential heating of land and ocean.
Albedo — fraction of solar radiation reflected by a surface; snow/ice ~0.8–0.9; forests ~0.1–0.2; oceans ~0.06; affects climate feedback.
Oceanography
Ocean composition — average salinity ~3.5% (35 ppt); dominated by sodium (Na+) and chloride (Cl−); salinity varies by evaporation, precipitation, and freshwater input.
Ocean layers — surface (mixed) zone (warm, well-lit, wind-mixed, to ~200 m); thermocline (sharp temperature decrease, ~200–1,000 m); deep zone (cold, ~2–4 °C, below ~1,000 m; vast majority of ocean volume).
Thermohaline circulation (THC) — global ocean conveyor belt driven by density differences from temperature (thermo) and salinity (haline). Cold, salty water sinks in the North Atlantic (NADW); connects all ocean basins; transports heat globally. Also called the Atlantic Meridional Overturning Circulation (AMOC).
Surface currents — driven by wind; shaped by Coriolis effect and continental boundaries. Clockwise gyres in NH, counterclockwise in SH. Key currents: Gulf Stream (warm, NW Atlantic), California Current (cold, E Pacific), Kuroshio Current (warm, W Pacific).
Upwelling — cold, nutrient-rich deep water rises to the surface (e.g., along the California coast, Peru coast); supports rich fisheries.
Tides — caused by gravitational pull of the Moon (primary) and Sun (secondary). Spring tides (highest range): Moon, Sun, Earth aligned (new and full moon). Neap tides (smallest range): Moon and Sun at right angles (quarter moon).
Waves — wind-generated surface waves; energy moves forward but water particles orbit in circles; wavelength, period, and amplitude relate to wind speed and fetch.
Ocean gyres — large rotating systems of ocean currents driven by wind and Coriolis; five major subtropical gyres (North/South Atlantic, North/South Pacific, Indian Ocean) rotate clockwise in the NH and counterclockwise in the SH; the North Pacific Subtropical Gyre collects floating plastic in the Great Pacific Garbage Patch.
Gulf Stream — warm, swift western boundary current in the North Atlantic; flows from the Gulf of Mexico northeastward to Europe; part of the wind-driven gyre system and feeds into the thermohaline circulation; moderates climate of Western Europe.
Mid-ocean ridges — continuous underwater mountain chain ~65,000 km long; form at divergent plate boundaries; the Mid-Atlantic Ridge runs nearly the full length of the Atlantic; the East Pacific Rise is faster-spreading and less rugged; the global mid-ocean ridge system is Earth’s longest mountain range.
Ocean trenches — deepest parts of the ocean; form where oceanic plates subduct; Mariana Trench (W. Pacific) contains Challenger Deep (~10,935 m), Earth’s deepest point; other examples: Tonga Trench, Japan Trench, Puerto Rico Trench.
Thermohaline circulation / AMOC — the “global conveyor belt”; cold, dense water sinks in the Labrador Sea and Nordic Seas, flows south as North Atlantic Deep Water (NADW), upwells in the Southern Ocean and Indian/Pacific Oceans; complete circuit takes ~1,000 years; freshwater input from melting ice sheets could weaken AMOC.
Spring and neap tides — spring tides occur at new and full moon (Sun, Moon, Earth aligned = syzygy); tidal range is maximum. Neap tides occur at first and third quarter moon (Sun and Moon at ~90°); tidal range is minimum; the Bay of Fundy (Nova Scotia) has the world’s largest tidal range (~16 m) due to resonance.
Turbidity — the cloudiness or haziness of a fluid caused by suspended particles (sediment, organic matter, microorganisms) that scatter light; measured in Nephelometric Turbidity Units (NTU) or Formazin Turbidity Units (FTU) using a nephelometer; high turbidity reduces light penetration (limiting photosynthesis), indicates elevated sediment or organic load, and can carry adsorbed contaminants; turbidity currents are underwater avalanches of dense, sediment-laden water that flow down continental slopes at high speed, depositing characteristic graded beds (turbidites) on the ocean floor; turbidites record episodic mass transport events and preserve a stratigraphic record of past earthquakes and slope failures.
Ocean acidification — absorption of atmospheric CO2 forms carbonic acid (H2CO3), lowering ocean pH; ocean surface pH has decreased from ~8.2 to ~8.1 since the industrial era (~0.1 units = ~26% increase in H+ concentration); threatens shell-forming organisms.
El Niño–Southern Oscillation (ENSO)
Normal conditions — trade winds push warm water westward; cold upwelling off Peru coast; thermocline tilts (deep in west, shallow in east).
El Niño — weakening or reversal of trade winds; warm water spreads east across the Pacific; SST anomaly ≥0.5 °C in Niño 3.4 region for ≥5 consecutive overlapping 3-month periods; causes droughts in Australia/SE Asia, flooding on Americas’ west coasts.
La Niña — enhanced trade winds; anomalously cool eastern Pacific; opposite precipitation effects; often follows El Niño.
Southern Oscillation — atmospheric pressure seesaw between the central-eastern Pacific (Tahiti) and Indian Ocean–western Pacific (Darwin); measured by the Southern Oscillation Index (SOI).
ENSO cycle — irregular period of ~2–7 years; significant global climate teleconnections.
The Climate System and Global Warming
Greenhouse effect and carbon cycle
Natural greenhouse effect — solar radiation passes through the atmosphere; Earth’s surface absorbs and re-emits infrared radiation; greenhouse gases (H2O, CO2, CH4, N2O, O3) absorb and re-emit IR, warming the surface. Without it, Earth’s mean surface temperature would be ~−18 °C instead of ~+15 °C.
Greenhouse gases (GHGs) — water vapor (largest natural contribution); CO2 (most important anthropogenic driver, long atmospheric lifetime ~centuries); CH4 (methane, ~28–36x CO2 global warming potential over 100 years, shorter lifetime); N2O (~273x CO2 GWP 100-yr); fluorinated gases (synthetic, very high GWP).
Carbon cycle — carbon moves among atmosphere, biosphere, soils, oceans, and lithosphere. Fast cycle: photosynthesis/respiration. Slow cycle: volcanic outgassing, carbonate-silicate weathering (Urey reaction), fossil fuel formation.
Milankovitch cycles — three periodic variations in Earth’s orbital parameters that affect solar insolation and drive ice ages: (1) eccentricity (ellipticity of orbit, ~100,000-year cycle); (2) obliquity (axial tilt, 22.1°–24.5°, ~41,000-year cycle); (3) precession (wobble of rotation axis, ~23,000-year cycle); proposed by Serbian mathematician Milutin Milanković in the 1920s; confirmed by deep-sea sediment core records in the 1970s (Hays, Imbrie, Shackleton 1976).
Pleistocene — the first epoch of the Quaternary period, spanning ~2.58 Ma to ~11,700 years ago; characterized by recurring glacial-interglacial cycles (ice ages); at the Last Glacial Maximum (LGM, ~20,000 years ago) ice sheets covered much of North America (Laurentide ice sheet) and northern Europe; sea levels were ~120 m lower, exposing land bridges (e.g., Beringia between Asia and North America); megafaunal extinctions (mammoths, mastodons, giant ground sloths) occurred at the end of the Pleistocene, likely from a combination of climate change and human hunting; succeeded by the Holocene interglacial (~11,700 years ago to present).
Ice ages / glacial-interglacial cycles — Earth has experienced multiple glacial periods during the Quaternary (~2.6 Ma–present); the last glacial maximum (LGM) peaked ~20,000 years ago; ice sheets covered much of North America and Northern Europe; current interglacial (Holocene) began ~11,700 years ago; earlier major ice ages include the Marinoan “Snowball Earth” (~635 Ma).
Hydrologic cycle — the continuous movement of water: evaporation (ocean is dominant source) → atmospheric transport → precipitation → surface runoff/infiltration → groundwater → return to ocean; driven by solar energy; key reservoirs: oceans (97%), glaciers (~2%), groundwater, lakes/rivers, atmosphere.
Aquifer — an underground layer of permeable rock or sediment that stores and transmits groundwater; confined aquifers are under pressure (artesian wells); the Ogallala (High Plains) aquifer underlies eight US states and is being depleted faster than recharge.
Karst topography — landscape formed by dissolution of soluble rocks (limestone, dolomite, gypsum) by slightly acidic groundwater; features include sinkholes, caves, disappearing streams, springs, and tower karst; examples: Mammoth Cave (Kentucky), Carlsbad Caverns (New Mexico), Guilin (China).
Water table — the upper surface of the saturated zone in an unconfined aquifer; fluctuates seasonally; the capillary fringe lies just above it.
Pre-industrial CO2 — ~280 ppm for the preceding ~10,000 years (Holocene); ice cores confirm this.
Keeling Curve — continuous CO2 measurement at Mauna Loa Observatory, Hawaii, since 1958 (Charles David Keeling); passed 420 ppm in 2023; shows annual oscillation (NH growing season) superimposed on rising trend.
Observed climate change
Global mean temperature — approximately 1.1–1.2 °C above pre-industrial baseline (~1850–1900) as of the early 2020s; 2023 and 2024 are the warmest years on instrumental record.
Sea level rise — ~3.7 mm/year current rate (accelerating); driven by thermal expansion of seawater and melting of ice sheets/glaciers.
Arctic amplification — Arctic warming ~2–4x the global mean rate; sea ice extent declining; positive feedbacks include ice-albedo feedback.
Extreme events — increased frequency and intensity of heat waves, heavy precipitation events; intensification of tropical cyclones; lengthening fire weather seasons.
IPCC and policy context
IPCC — Intergovernmental Panel on Climate Change; established 1988 by UNEP and WMO; synthesizes published science in assessment reports (AR); does not conduct original research.
AR6 (2021–2022) — Sixth Assessment Report; concluded human influence is “unequivocal”; 1.5 °C above pre-industrial levels likely reached in the early 2030s without deep emissions cuts.
Paris Agreement (2015) — international treaty to hold warming to well below 2 °C and pursue 1.5 °C; nationally determined contributions (NDCs); not legally binding on emissions levels.
Feedback loops — positive: ice-albedo, water vapor, permafrost methane release; negative: Planck response (increased outgoing IR as temperature rises), lapse rate feedback (tropics). Net feedback is positive, amplifying warming.
Climate sensitivity — equilibrium climate sensitivity (ECS): expected global warming from a doubling of CO2 once equilibrium is reached; AR6 assessed likely range 2.5–4 °C, best estimate 3 °C.
Key Figures
Georgius Agricola — German scholar (1494–1555); De Re Metallica (1556) systematized mining, mineralogy, and metallurgy; often called the father of mineralogy.
James Ussher — Archbishop of Armagh; calculated from Biblical genealogies that Earth was created in 4004 BC (published 1650); exemplifies pre-scientific chronology that radiometric dating superseded.
Comte de Buffon (Georges-Louis Leclerc) — French naturalist; conducted cooling-sphere experiments (~1778) and estimated Earth’s age at ~75,000 years, far older than the Ussher date; early empirical challenge to scriptural chronology.
Georges Cuvier — French zoologist (1769–1832); founded vertebrate paleontology; championed catastrophism (Earth shaped by sudden violent events, each followed by new creation); recognized extinction as a fact from fossil evidence.
Eduard Suess — Austrian geologist (1831–1914); named Gondwanaland for the southern supercontinent (from rock and fossil correlations); also named the Tethys Sea and coined “biosphere.”
J. Tuzo Wilson — Canadian geophysicist (1908–1993); proposed transform faults and hot-spot theory; the Wilson cycle describes the opening and closing of ocean basins (rift → ocean → subduction → collision → suture).
Charles Lyell — established uniformitarianism in geology: “the present is the key to the past” (Principles of Geology, 1830–1833).
James Hutton — father of modern geology; recognized the deep age of Earth from rock cycle observations (18th century).
Andrija Mohorovičić — discovered the crust-mantle boundary from seismic data (1909).
Charles David Keeling — began continuous atmospheric CO2 measurements at Mauna Loa (1958); the record bears his name.
Svante Arrhenius — first to calculate quantitatively that doubling CO2 would warm Earth’s surface (~1896); underestimated feedbacks but got the sign right.
Luis and Walter Alvarez — proposed the asteroid impact hypothesis for the K-Pg extinction based on iridium layer evidence (1980).
Willi Köppen — developed the Köppen climate classification system (early 20th century).
William Smith — English geologist (1769–1839); produced the first nationwide geological map (of England, Wales, and part of Scotland, 1815); established the principle of faunal succession (strata can be identified by the fossils they contain); called the “Father of English Geology.”
Charles Richter — American seismologist (1900–1985); developed the Richter magnitude scale (ML) in 1935 with Beno Gutenberg; the scale was designed for Southern California earthquakes recorded on Wood-Anderson seismographs; largely replaced by the moment magnitude scale for large events.
Beno Gutenberg — German-American seismologist (1889–1960); identified the core-mantle boundary (Gutenberg discontinuity); co-developed the Richter scale; established the Gutenberg-Richter law relating earthquake frequency to magnitude.
Uniformitarianism — the principle that the same geological processes operating today operated in the past at the same general rates; championed by James Hutton and systematized by Charles Lyell; contrasts with catastrophism; the famous summary is Hutton’s “no vestige of a beginning, no prospect of an end” and Lyell’s “the present is the key to the past.”
Hutton’s unconformity — James Hutton’s observation at Siccar Point, Scotland (1788) of tilted Silurian greywacke overlain by horizontal Devonian sandstone; demonstrated an enormous time gap and the cyclical nature of geological processes; key evidence for deep time.
Harry Hess — American geologist (1906–1969); proposed seafloor spreading in his 1962 paper “History of Ocean Basins”; argued that new crust forms at mid-ocean ridges and old crust is destroyed at trenches; sometimes called the “Father of Plate Tectonics” alongside Wegener.
Alfred Wegener — German meteorologist and geophysicist (1880–1930); proposed continental drift in Die Entstehung der Kontinente und Ozeane (1915); cited matching coastlines, identical rock formations, and fossil correlations (e.g., Glossopteris flora, Mesosaurus); died on the Greenland ice sheet; his mechanism (an unknown force moving continents) was wrong, but his core hypothesis was vindicated by plate tectonics.
J. Harlen Bretz — American geologist (1882–1981) who proposed (1923) that the Channeled Scablands of eastern Washington were carved by catastrophic glacial outburst floods (Missoula Floods) from Glacial Lake Missoula; the idea was ridiculed for decades but ultimately confirmed; awarded the Penrose Medal in 1979 at age 96.
Marie Tharp — American geologist and cartographer (1920–2006) who mapped the ocean floor with Bruce Heezen; her 1952 discovery of the rift valley at the center of the Mid-Atlantic Ridge provided crucial evidence for seafloor spreading; her work was initially dismissed by Heezen, who called it “girl talk.”
verify: Walther Penck vs. William Morris Davis — Penck’s parallel slope retreat model vs. Davis’s cycle of erosion (peneplanation) are a common comparative question in geomorphology; confirm which processes each is associated with before using in a clue.
verify: Exact depth of the Mohorovičić discontinuity — commonly cited as ~5–10 km under ocean, ~30–50 km under continents, but values vary by source; confirm the standard figures used in quizbowl literature.
verify: Laurentia vs. Laurasia — Laurentia refers specifically to the ancient North American craton; Laurasia is the Mesozoic northern supercontinent (North America + Eurasia); these are frequently confused and conflated in quizbowl questions.
verify: “Great Oxygenation Event” timeline — commonly cited at ~2.4 Ga; some sources argue for an earlier oxygenation pulse; confirm the canonical date for competitive play.
Peridotite — the dominant rock of Earth’s upper mantle; composed mainly of olivine and pyroxene; intrinsically ultramafic (very low SiO2, <45%); occasionally brought to the surface as xenoliths in basaltic or kimberlite eruptions; kimberlite pipes (source of diamonds) are peridotite-bearing diatremes.
Granite — coarse-grained felsic intrusive rock; composed of quartz, orthoclase feldspar, plagioclase, and mica; forms the cores of mountain ranges (batholiths); characteristic rock of continental crust; specific gravity ~2.7.
Uniformly distributed mass extinctions — the Big Five are supplemented in quizbowl by noting each boundary: the Ordovician-Silurian extinction (~444 Ma) may have been triggered by a gamma-ray burst and glaciation; the Late Devonian (Kellwasser event, ~372 Ma) affected reef ecosystems; the Triassic-Jurassic (~201 Ma) was likely caused by the CAMP (Central Atlantic Magmatic Province) flood basalts.
Phreatic vs. magmatic eruption — phreatic (steam-blast) eruptions are caused by water flashing to steam when heated by magma; no new magma is expelled; can occur without warning (e.g., Ontake 2014); magmatic eruptions involve fresh magma reaching the surface.
Subduction — process by which denser oceanic lithosphere sinks into the mantle beneath lighter lithosphere; generates deep-focus earthquakes (down to ~670 km); produces island arcs or Andean-type volcanic arcs; slab dehydration releases fluids that lower the mantle wedge’s melting point, producing water-fluxed melting.
P-wave shadow zone detail — P-waves are refracted (bent) as they pass through the liquid outer core, creating a zone between ~103° and ~142° from the epicenter where direct P-waves do not arrive; S-waves are completely blocked from ~103° onward; first described by Richard Oldham (1906).
Glacial features — U-shaped valleys (glacial erosion vs. V-shaped river valleys); cirques (bowl-shaped bedrock basins where glaciers form); arêtes (sharp ridges between cirques); moraines (ridges of glacially deposited till): terminal/end, lateral, medial, ground; drumlins (streamlined hills formed under moving glaciers); kettles (depressions from melted ice blocks); eskers (sinuous ridges of glaciofluvial sediment).