Every Earth Science concept in the middle school Science Bowl study set (grades 6-8), 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.
Crust: thin, rocky outer layer (oceanic crust is thinner and denser than continental crust). Mantle: largest layer; hot, solid rock that flows slowly (convection drives plate movement). Outer core: liquid iron-nickel; generates Earth's magnetic field. Inner core: solid iron-nickel; hottest part. Evidence from seismic waves (P and S waves).
Igneous rocks: formed when magma or lava cools (granite = slow cooling; basalt = fast cooling). Sedimentary rocks: formed from compacted and cemented sediments (sandstone, limestone, shale). Metamorphic rocks: changed by heat and pressure (marble from limestone; quartzite from sandstone). Any rock type can become another through the rock cycle.
Earth's crust is divided into large plates that move slowly (a few centimeters per year) driven by convection in the mantle. Convergent boundaries: plates collide (form mountains or trenches). Divergent boundaries: plates pull apart (form rift valleys or mid-ocean ridges). Transform boundaries: plates slide past each other (earthquakes). Evidence: fit of continents, fossil distribution, magnetic striping.
Atmosphere: layers of gas held by gravity. Troposphere (lowest): where weather occurs; temperature decreases with altitude. Stratosphere: contains the ozone layer (absorbs UV radiation). Weather is the short-term state of the atmosphere; climate is the long-term average. Water vapor, clouds, and wind transfer energy in the atmosphere. Air masses and fronts cause weather changes.
The continuous movement of water through Earth's systems. Evaporation: liquid water becomes water vapor (heat from Sun drives this). Transpiration: plants release water vapor. Condensation: water vapor cools and forms clouds around condensation nuclei. Precipitation: water falls as rain, snow, sleet, or hail. Runoff and infiltration return water to oceans and groundwater.
The Sun (a star) is at the center. Eight planets in order: Mercury, Venus, Earth, Mars (inner, rocky), Jupiter, Saturn, Uranus, Neptune (outer, gas/ice giants). Asteroid belt between Mars and Jupiter. Comets are icy bodies with long orbits around the Sun. Pluto is a dwarf planet in the Kuiper Belt. Planets orbit the Sun due to gravity.
The Moon orbits Earth in about 29.5 days. Moon phases are caused by the relative positions of the Sun, Earth, and Moon: new moon → crescent → quarter → gibbous → full. Lunar eclipse: Earth's shadow falls on the Moon (full moon). Solar eclipse: Moon blocks the Sun's light from reaching Earth (new moon). The Moon's gravity causes tides.
Weathering: breaking down rocks. Mechanical weathering: rock breaks into smaller pieces without chemical change (freeze-thaw, root growth, abrasion). Chemical weathering: minerals in rock change (acid rain dissolves limestone, rusting of iron-rich rock). Erosion: transport of weathered material by water, wind, ice, or gravity. Deposition: sediment is dropped when the agent slows.
Minerals are naturally occurring, inorganic solids with a definite chemical composition and crystal structure. Identified by hardness (Mohs scale, 1–10), color, luster (shiny or dull), streak, cleavage, and specific gravity. Rocks are mixtures of minerals. Most common minerals: quartz, feldspar, mica. Diamond is the hardest mineral (10); talc is the softest (1).
Volcanoes form where magma (molten rock) reaches Earth's surface. Most occur at plate boundaries or over hot spots (like Hawaii). Lava: magma that reaches the surface. Pyroclastic material: fragments of rock and ash ejected during eruption. Types: shield volcanoes (broad, gentle slopes, runny lava, less explosive — Hawaii); stratovolcanoes/composite (steep, explosive, thick lava — Mt. St. Helens, Mt. Fuji). Volcanic gases: steam, CO₂, SO₂. Lahars are dangerous volcanic mudflows. Volcanic ash can affect climate by blocking sunlight.
Earthquakes: sudden shaking of Earth's crust caused by the release of energy stored in rocks under stress. Fault: fracture in rock where movement occurs. Focus (hypocenter): underground point where earthquake originates. Epicenter: point on Earth's surface directly above the focus. Seismic waves: P-waves (compressional, fastest, travel through solids and liquids) and S-waves (shear, only through solids). Surface waves cause most damage. Richter scale (or moment magnitude): measures energy released. Most earthquakes occur at plate boundaries.
Seasons are caused by Earth's 23.5° axial tilt relative to its orbital plane, NOT by Earth's distance from the Sun. When the Northern Hemisphere tilts toward the Sun → summer (more direct sunlight, more hours of daylight, more energy per area). Tilted away → winter. Solstices: June 21 (summer in NH, winter in SH); December 21 (winter in NH, summer in SH). Equinoxes: ~March 20 and September 22 (equal day and night; neither hemisphere tilted toward Sun). Tropics of Cancer and Capricorn: 23.5°N and S.
Day and night are caused by Earth's rotation on its axis (one rotation = 24 hours). The side facing the Sun experiences day; the opposite side experiences night. Earth rotates from west to east (counterclockwise viewed from north pole) → Sun appears to rise in the east and set in the west. Earth is divided into 24 time zones, each 15° of longitude wide (360° / 24 hours). The International Date Line (180° longitude) marks where the date changes. The prime meridian (0° longitude) passes through Greenwich, England.
Sunlight zone (epipelagic, 0–200 m): receives sunlight; most photosynthesis and marine life. Twilight zone (mesopelagic, 200–1000 m): dim light; bioluminescent organisms. Midnight zone (bathypelagic, 1000–4000 m): no light; cold, high pressure. Abyssal zone (4000–6000 m): near-freezing, extreme pressure; unique organisms at hydrothermal vents. Hadal zone: ocean trenches (>6000 m). The ocean covers 71% of Earth's surface; average depth ~3,800 m; deepest point: Mariana Trench (~11,000 m). Salinity: ~3.5% (mostly NaCl).
Rivers: freshwater flowing downhill due to gravity; carry sediment; form canyons, valleys, deltas. Tributaries: smaller streams flowing into a larger river. Watershed/drainage basin: all land draining to a river. Lakes: inland bodies of standing water. Eutrophication: excess nutrients → algal blooms → oxygen depletion → dead zones. Wetlands (marshes, swamps, bogs): transitional between aquatic and terrestrial; extremely productive; filter pollutants, store floodwater, provide habitat. The Amazon is the world's largest river by discharge volume.
Deserts receive less than 25 cm of precipitation per year. Hot deserts (Sahara, Arabian): extreme daytime heat, cold nights, sand dunes and rock formations. Cold deserts (Gobi, Antarctica): cold temperatures; Antarctica is the largest and driest desert on Earth. Desert organisms: adapted for water conservation (cacti: store water in thick stems, deep/wide roots; camels: fatty humps, water-efficient kidneys). Desertification: expansion of desert due to overgrazing, deforestation, and climate change. Oases: areas with water sources in deserts.
The Sun is a medium-sized star (yellow dwarf; spectral type G) about 150 million km from Earth. It is a giant ball of hot plasma held together by gravity. Energy produced by nuclear fusion in the core (hydrogen → helium). Layers: core, radiative zone, convective zone, photosphere (visible surface, ~5,500°C), chromosphere, corona (outermost, millions of °C). Sunspots: cooler dark regions on surface (magnetic activity). Solar flares and coronal mass ejections (CMEs) can disrupt Earth's magnetic field and communication systems.
Planets: orbit the Sun, have cleared their orbital neighborhood. Rocky/terrestrial (inner): Mercury, Venus, Earth, Mars — small, dense, few moons. Gas giants (outer): Jupiter, Saturn — large, low density, many moons, ring systems. Ice giants: Uranus, Neptune — contain ices (water, ammonia, methane). Dwarf planets: Pluto, Eris, Ceres (in asteroid belt). Asteroid belt: between Mars and Jupiter; mostly rock and metal. Kuiper Belt: icy objects beyond Neptune. Comets: icy nuclei; form two tails (ion tail away from Sun; dust tail along orbit) when near Sun.
Key missions: Sputnik (1957, first satellite, USSR), Yuri Gagarin (1961, first human in space, USSR), Apollo 11 (1969, first Moon landing, Neil Armstrong & Buzz Aldrin). Mars rovers: Curiosity, Perseverance. Hubble Space Telescope: launched 1990, orbits Earth, images deep space. James Webb Space Telescope (2021): infrared observations, images early universe. International Space Station (ISS): research laboratory in low Earth orbit. Voyager probes: now in interstellar space. Private companies (SpaceX, Blue Origin) advancing rocket technology.
Earth's atmosphere is ~78% nitrogen (N₂), ~21% oxygen (O₂), ~0.93% argon (Ar), ~0.04% carbon dioxide (CO₂), plus trace gases and water vapor. Air has mass → exerts pressure on everything below it. Atmospheric pressure decreases with altitude (less air above). Measured with a barometer; standard pressure = 1 atm = 101,325 Pa = 760 mmHg. High pressure areas: air sinks → clear weather. Low pressure areas: air rises → clouds and precipitation. Isobars: lines of equal pressure on weather maps.
Wind: movement of air from high pressure to low pressure areas. Local winds: sea breeze (land heats faster than water → air rises over land → sea air flows in; reverses at night as land breeze). Mountain and valley breezes. Global wind patterns: trade winds (blow from subtropical high-pressure zones toward equator), westerlies (mid-latitudes), polar easterlies. Beaufort scale: measures wind speed. Jet streams: fast high-altitude air currents that steer weather systems. Coriolis effect: deflects winds to the right in NH, left in SH.
Humidity: amount of water vapor in air. Relative humidity: ratio of water vapor present to maximum possible at that temperature (expressed as %); 100% = saturated. Dew point: temperature at which air cools to saturation and condensation begins. Clouds form when rising air cools to the dew point, and water vapor condenses around tiny particles (condensation nuclei: dust, pollen). Cloud types: cumulus (puffy, fair weather), stratus (flat layers, overcast), cirrus (high, wispy, ice crystals), cumulonimbus (thunderstorm clouds — tall, dark, anvil-shaped).
Thunderstorms: form from cumulonimbus clouds; lightning (static discharge between clouds or cloud to ground) and thunder (shock wave from rapid air expansion). Hail: ice pellets formed in strong updrafts. Tornadoes: violently rotating column of air extending from cumulonimbus cloud to ground; most common in 'Tornado Alley' (central US); rated by Fujita/Enhanced Fujita scale (EF0–EF5). Hurricanes/typhoons: large rotating tropical storms (sustained winds >119 km/h); form over warm ocean water (≥26°C); rated Category 1–5 (Saffir-Simpson scale); lose strength over land.
Natural resources: materials from Earth used by humans. Renewable resources: naturally replenished on human timescales (solar energy, wind, water, biomass, soil). Non-renewable resources: form over millions of years; limited supply (fossil fuels — coal, oil, natural gas; mineral ores). Inexhaustible resources: essentially unlimited (sunlight, wind). Conservation: using resources wisely to prevent depletion. Recycling: reprocessing materials (aluminum, glass, plastic, paper) reduces need for new resources. Sustainable development: meets present needs without compromising future generations' ability to meet their needs.
Fossils: preserved remains or traces of ancient organisms. Types: body fossils (preserved hard parts: bones, shells, teeth), trace fossils (footprints, burrows, tracks), mold (cavity left by organism), cast (mold filled with minerals), amber (organism preserved in tree resin), petrification (minerals replace organic material). Index fossils: organisms that lived during short, well-defined time periods; used to date rock layers and correlate strata across regions. Law of Superposition: in undisturbed layers, lower layers are older. Relative vs absolute dating.
Topographic maps: show elevation using contour lines (lines connecting points of equal elevation); closely spaced contour lines = steep slope; V-shaped contours pointing uphill indicate valleys. GPS: uses satellites to determine latitude, longitude, and altitude. Latitude: degrees north or south of equator (0°–90°). Longitude: degrees east or west of prime meridian (0°–180°). Seismographs detect and record seismic waves. Weather instruments: thermometer (temperature), barometer (pressure), anemometer (wind speed), rain gauge (precipitation), hygrometer (humidity).
Soil erosion: removal of topsoil by water, wind, or ice. Water erosion: surface runoff carries soil; more severe on steep slopes without vegetation. Wind erosion: common in dry, barren areas (Dust Bowl, 1930s USA). Loss of topsoil reduces agricultural productivity. Conservation methods: contour plowing (plowing along hillside contour lines to slow runoff), terracing (cut flat steps into hillside), windbreaks (rows of trees block wind), cover crops (plants protect soil when fields are bare), no-till farming (leaving crop residues to hold soil), reforestation.
Deforestation: large-scale removal of forests. Causes: agriculture (mainly for cattle and soybeans in Amazon), logging, urban expansion, road building. Consequences: loss of biodiversity (forests contain ~50% of all species), increased carbon dioxide (trees store carbon; burning/decomposing releases CO₂), soil erosion and flooding (tree roots hold soil, absorb water), disruption of water cycle (less transpiration → less rainfall in some regions). Amazon rainforest: largest tropical forest; major carbon sink; often called 'lungs of the Earth'.
Global warming: long-term increase in Earth's average surface temperature. Caused by enhanced greenhouse effect: burning fossil fuels (coal, oil, natural gas) → releases CO₂ → traps more heat. Evidence: rising global temperatures, melting glaciers and Arctic ice, rising sea levels, extreme weather events becoming more frequent. Effects: more intense hurricanes, droughts, heat waves, flooding of coastal cities, coral bleaching, shifts in species ranges. Solutions: reducing fossil fuel use, switching to renewable energy, reforestation, energy efficiency improvements.
Earth is approximately 4.6 billion years old. Geologic time is divided into eons, eras, periods, and epochs. Major eras: Paleozoic (541–252 million years ago — invertebrates, fish, amphibians, reptiles, forests), Mesozoic (252–66 Mya — dinosaurs, first birds and mammals; ended with mass extinction), Cenozoic (66 Mya–present — mammals dominant, eventually humans). Relative dating: using rock layers to determine order of events (older layers below). Absolute dating: using radioactive decay to determine actual age in years (radiometric dating).
Alfred Wegener (1912) proposed that continents were once joined in a supercontinent called Pangaea and have since drifted apart. Evidence: fit of continents (South America and Africa fit together), matching fossils on different continents (Mesosaurus found in both South America and Africa), matching rock formations across oceans, glacial striations in tropical regions. Mechanism (not understood in Wegener's time): seafloor spreading and plate tectonics driven by mantle convection. Pangaea began breaking apart ~175–200 million years ago.
Tsunamis: series of large ocean waves generated by sudden displacement of the ocean floor, usually by submarine earthquakes, landslides, or volcanic eruptions. In deep ocean: long wavelength (~200 km), low wave height (~1 m), travel at ~800 km/h. Near shore: wavelength decreases, height increases dramatically (shoaling). Warning signs: earthquake, then sea withdrawal before waves arrive. Coastal hazards: storm surge (hurricane pushes ocean inland), coastal erosion, sea level rise. Seawalls, mangrove forests, and early warning systems help protect coastlines.
Mountains form in several ways. Fold mountains: two continental plates collide, crust buckles and folds upward (Himalayas — India-Asia collision; Alps — Africa-Europe). Fault-block mountains: blocks of crust lifted or tilted along faults (Sierra Nevada). Dome mountains: magma pushes up crust without erupting (Black Hills). Volcanic mountains: lava builds up over hotspot or subduction zone (Cascade Range, Andes). Erosion by water, wind, and ice sculpts mountain shapes over millions of years. Highest peak: Mt. Everest (8,849 m), Himalayan range.
Surface ocean currents: driven by global winds; gyres rotate clockwise in NH, counterclockwise in SH (Coriolis effect). Warm currents (Gulf Stream) bring heat from tropics to higher latitudes, warming nearby land (Western Europe is warmer than equivalent latitude in North America). Cold currents bring nutrients upward (upwelling), supporting fisheries. Thermohaline circulation (ocean conveyor belt): driven by density differences (cold, salty water sinks in North Atlantic; drives global ocean mixing). El Niño: weakening of trade winds warms eastern Pacific, affecting global weather patterns.
The ozone layer in the stratosphere (15–35 km above Earth) absorbs most of the Sun's harmful ultraviolet (UV) radiation. UV-B causes sunburn, skin cancer, cataracts, and harms marine ecosystems. CFCs (chlorofluorocarbons — used in old refrigerators and aerosol sprays) destroy ozone catalytically. An 'ozone hole' forms over Antarctica each spring. Montreal Protocol (1987): international agreement that phased out CFC production; ozone layer is slowly recovering. Sunscreen blocks UV radiation from reaching skin.
Canyon: deep, steep-sided valley carved by a river (Grand Canyon — carved by Colorado River over ~5-6 million years). Cave/cavern: underground opening formed by chemical weathering of limestone by slightly acidic groundwater (karst topography; stalactites hang from ceiling — 'c' for ceiling; stalagmites grow up from floor — 'g' for ground). Geyser: hot spring that periodically erupts with steam and water (Yellowstone; water heated by magma). Sinkhole: collapse of ground above a cave. Arch: erosion creates natural rock bridge.
Climate is primarily determined by latitude (distance from equator). Near equator (0°–23.5°): tropical climate — hot year-round, high solar energy input. Subtropical (~23.5°–35°): hot, dry — deserts (Sahara, Australian Outback). Mid-latitudes (35°–60°): temperate — four seasons; forests and grasslands. Subarctic (60°–66.5°): boreal forest (taiga) — cold winters, cool summers. Arctic/Antarctic circles (66.5°+): tundra and ice sheets — very cold, permafrost. Altitude also affects climate: higher elevation → colder, similar to higher latitude. Ocean proximity moderates temperatures.