OSAT Earth Science (OK108) cheat sheet

Scientific method sequence: observation → question → hypothesis → prediction → controlled test → analysis → peer review → replication; a hypothesis must be falsifiable to count as scientific.

Variables: independent = manipulated by investigator; dependent = measured response; controlled variables held constant. A control group receives no treatment and establishes baseline.

Earth science is historically and spatially constrained: deep time (4.54 Ga), vast spatial scales, and non-repeatable events require multiple converging lines of evidence rather than direct experiment.

Measurement rules: SI base units (m, kg, s, K, mol, A, cd); precision = reproducibility of a measurement, accuracy = closeness to true value; random error scatters, systematic error shifts all readings.

Significant figures: multiplication/division keep the least number of sig figs; addition/subtraction keep the least number of decimal places; report uncertainty with one sig fig.

Density = mass/volume (g/cm³); used to identify minerals, explain isostasy, and drive subduction. Earth's mean density ~5.5 g/cm³ vs crust ~2.7–3.0 g/cm³ implies a dense metallic core.

Maps and imagery: topographic contour lines connect equal elevation; contour spacing indicates slope steepness; GIS layers, Landsat, and GPS/GNSS geodesy are standard Earth-observation tools.

Relative vs absolute dating: superposition, cross-cutting, and faunal succession give order; radiometric decay (half-life) gives numeric ages. Isotope systems: U-Pb, K-Ar, Rb-Sr, C-14 (short range only).

Models and uncertainty: Earth system models are tested by hindcasting; correlation does not establish causation; report confidence intervals and distinguish hypothesis, theory, and law.

Earth's rotation on its axis (west to east) causes day/night and apparent daily motion of stars; one sidereal day = 23 h 56 min 4 s, one solar day = 24 h.

Earth's revolution plus 23.5° axial tilt causes seasons; solstices occur when a hemisphere is tilted most toward/away from the Sun (~June 21, ~Dec 21); equinoxes (~Mar 20, ~Sep 22) have ~12 h daylight everywhere.

Moon phases result from changing Sun–Moon–Earth geometry: new → waxing crescent → first quarter → waxing gibbous → full → waning gibbous → third quarter → waning crescent; cycle = 29.5 days (synodic).

Solar eclipse: Moon between Earth and Sun, only at new moon; lunar eclipse: Earth between Sun and Moon, only at full moon. Eclipses are rare because the lunar orbit is inclined ~5° to the ecliptic.

Tides: two bulges from differential gravity plus centrifugal effect; spring tides at new and full moon (aligned), neap tides at quarters (perpendicular). Most coasts are semidiurnal.

Kepler's laws: orbits are ellipses with Sun at one focus; equal areas in equal times (faster at perihelion); P² ∝ a³. Newton's gravity F = Gm₁m₂/r² explains orbital motion.

Solar system structure: terrestrial planets (Mercury, Venus, Earth, Mars) are small, dense, rocky; Jovian planets (Jupiter, Saturn, Uranus, Neptune) are large, low density, gas/ice giants with ring systems and many moons.

Stellar life cycle: nebula → protostar → main sequence (H fusion) → red giant/supergiant → planetary nebula + white dwarf (low mass) or supernova + neutron star/black hole (high mass). Sun is a G-type main-sequence star ~4.6 Ga old.

Universe evidence: Hubble expansion (redshift), cosmic microwave background (~2.7 K), and light-element abundances support Big Bang ~13.8 Ga; Doppler/spectroscopy reveals composition and motion.

Mineral definition: naturally occurring, inorganic solid, ordered crystalline structure, definite chemical composition (or limited solid solution). ~4,000+ known minerals; silicates dominate the crust.

Silicate structures: isolated tetrahedra (olivine), single chains (pyroxene), double chains (amphibole), sheets (mica, clay), frameworks (quartz, feldspar). More shared oxygens → higher Si:O ratio → higher melting temperature and lower density.

Mohs hardness scale: talc 1, gypsum 2, calcite 3, fluorite 4, apatite 5, orthoclase 6, quartz 7, topaz 8, corundum 9, diamond 10. Hardness is a diagnostic property, not a continuous scale.

Other diagnostic properties: cleavage vs fracture, luster (metallic/nonmetallic), streak, color (least reliable), specific gravity, reaction with dilute HCl (calcite), magnetism (magnetite), taste (halite).

Igneous classification by composition and texture: felsic (high Si, low density, light color) to mafic/ultramafic (low Si, high density, dark); texture (aphanitic, phaneritic, porphyritic, glassy, vesicular) records cooling rate.

Bowen's reaction series: discontinuous branch olivine → pyroxene → amphibole → biotite; continuous branch Ca-plagioclase → Na-plagioclase; then orthoclase → muscovite → quartz at lowest temperature.

Sedimentary rocks: clastic (conglomerate, sandstone, shale) classified by grain size; chemical/biochemical (limestone, chert, rock salt, coal). Sorting, rounding, and cement record transport and deposition.

Metamorphic rocks: foliated (slate → phyllite → schist → gneiss) from increasing heat/pressure; nonfoliated (marble from limestone, quartzite from sandstone, hornfels). Index minerals (chlorite, biotite, garnet, staurolite, kyanite, sillimanite) map metamorphic grade.

Rock cycle: igneous, sedimentary, and metamorphic rocks transform by melting, weathering/erosion/deposition/lithification, heat/pressure, and deformation; no fixed path, and any rock type can become any other.

Earth's interior layers: crust (continental ~35 km, oceanic ~7 km), mantle (to ~2,900 km), outer core (liquid Fe-Ni, generates magnetic field via dynamo), inner core (solid). Boundaries: Mohorovičić (crust/mantle), Gutenberg (mantle/core).

Seismic waves: P waves (compressional, fastest, travel through solids/liquids), S waves (shear, slower, cannot pass liquids - evidence for liquid outer core), surface waves (slowest, most damaging).

Plate boundaries: divergent (mid-ocean ridges, continental rifts, normal faults, shallow quakes), convergent (subduction zones/trenches, volcanic arcs, deep quakes; continental collision builds mountains), transform (lateral sliding, e.g., San Andreas, strike-slip).

Driving mechanisms: slab pull (dominant), ridge push, and mantle convection. Seafloor magnetic striping and age patterns (Hess/ Vine-Matthews) confirm seafloor spreading.

Hotspots: intraplate volcanism (Hawaii, Yellowstone) that produces age-progressive chains recording plate motion direction and rate.

Stress and faults: compressional stress → reverse/thrust faults; tensional → normal faults; shear → strike-slip. Hanging wall up = reverse; down = normal.

Folds: anticline (upward-arching, oldest rocks in core), syncline (downward, youngest in core); plunging folds create V-shaped outcrop patterns; domes and basins are circular equivalents.

Unconformities: angular (tilted layers truncated), disconformity (erosion surface between parallel beds), nonconformity (sedimentary over igneous/metamorphic). Uniformitarianism: present processes explain the past.

Earthquake magnitude vs intensity: moment magnitude (Mw) is logarithmic energy measure; Modified Mercalli intensity describes observed damage, which depends on distance, substrate, and building design.

Weathering breaks rock in place: physical (frost wedging, salt crystal growth, exfoliation/unloading, thermal expansion, biological) and chemical (hydrolysis of feldspar to clay, oxidation, carbonation/dissolution of limestone, acid attack).

Erosion agents and landforms: running water (V-shaped valleys, meanders, deltas, alluvial fans), glaciers (U-shaped valleys, moraines, drumlins, striations, erratics), wind (yardangs, ventifacts, dunes, loess), waves (sea cliffs, sea stacks, spits).

Mass wasting classification by material and motion: creep, slump, debris flow, mudflow, rockfall, rockslide; triggered by slope steepening, water saturation, loss of vegetation, earthquakes.

Drainage patterns: dendritic (uniform material), trellised (folded strata), radial (dome/volcano), rectangular (jointed rock). Watersheds divide flow by topography.

Stream processes: velocity rises with discharge and channel slope; competence = largest particle size moved; capacity = total load; deposition occurs when velocity drops (sorted by size).

Soil formation factors: parent material, climate, topography, organisms, time (CLORPT). Horizons: O (organic), A (topsoil, humus), E (eluviation), B (subsoil, illuviation), C (weathered parent), R (bedrock).

Soil texture triangle classifies sand/silt/clay percentages; loam is a balanced mixture. Texture controls porosity, permeability, water retention, and fertility.

Karst and groundwater: high water table → higher discharge, less bank storage; permeability and porosity determine aquifer yield; limestone dissolution forms caves, sinkholes, disappearing streams.

Human impacts: accelerated erosion from deforestation and poor farming, salinization from irrigation, desertification, and contamination of aquifers; conservation practices include terracing, contour plowing, cover crops, windbreaks.

Geologic time scale (largest to smallest): eons (Hadean, Archean, Proterozoic, Phanerozoic) → eras (Paleozoic, Mesozoic, Cenozoic) → periods → epochs. Phanerozoic boundaries mark major extinctions.

Key events: Earth forms ~4.54 Ga; oldest rocks ~4.0 Ga; first life ~3.5 Ga (prokaryotes); Great Oxidation Event ~2.4 Ga; Cambrian explosion ~541 Ma; Permian-Triassic extinction ~252 Ma (~90% marine species); K-Pg extinction ~66 Ma (asteroid, Chicxulub) ends dinosaurs.

Stratigraphic principles: superposition (younger above older), original horizontality, lateral continuity, cross-cutting relationships (faults/intrusions younger than what they cut), inclusions (older than host), faunal succession.

Correlation uses lithology, index fossils, marker beds, and radiometric dates. Index fossils are widespread, short-lived, and abundant (e.g., trilobites, ammonites, graptolites).

Radiometric dating: parent decays to daughter at known half-life; N = N₀(1/2)^(t/t½); the ratio of parent to daughter gives age. C-14 useful only to ~50,000 years; U-Pb for ancient rocks.

Fossils: preservation types include permineralization, molds and casts, amber, ice, carbon films, and trace fossils (footprints, burrows). Body fossils require rapid burial and hard parts.

Relative vs numeric ages: relative ordering from stratigraphy; numeric from isotopes. The geologic record is incomplete (unconformities, erosion, metamorphism) so gaps exist.

Plate tectonics and paleoclimate: fossil and glacial evidence (Glossopteris, Gondwana tillites) supported continental drift; ice ages, greenhouse periods, and sea-level change are recorded in strata and isotopes.

Evolution and extinction in the record: mass extinctions open ecological niches; adaptive radiation follows (e.g., mammals diversify after K-Pg); fossils document transitional forms and change over time.

Atmospheric layers: troposphere (weather, temperature decreases with altitude), stratosphere (ozone layer, temperature increases), mesosphere, thermosphere, exosphere. Pressure decreases with altitude.

Composition: ~78% N₂, 21% O₂, ~1% argon, variable CO₂ (~0.04%) and water vapor; greenhouse gases (CO₂, H₂O, CH₄, N₂O) absorb outgoing infrared radiation.

Energy balance: incoming solar shortwave vs outgoing longwave; albedo reflects, absorption heats; uneven heating drives convection and global circulation (Hadley, Ferrel, Polar cells).

Air masses: cP, cT, mP, mT classified by source region; fronts: cold (steep, fast, thunderstorms), warm (gentle, steady rain), stationary, occluded.

Clouds: stratus (layered), cumulus (puffy), cirrus (high ice); precipitation forms by collision-coalescence and Bergeron (ice crystal) processes.

Pressure systems: low pressure = converging, rising air, clouds and precipitation; high pressure = diverging, sinking air, clear skies. Winds blow from high to low, deflected by Coriolis (right in NH, left in SH).

Severe weather: thunderstorms need moisture, instability, lift; tornadoes form in supercells; hurricanes require warm ocean (>26 °C), low shear, and Coriolis effect away from the equator.

Climate controls: latitude, altitude, proximity to water, ocean currents, prevailing winds, and topography (rain shadow). Köppen classification groups climates by temperature and precipitation.

Climate change evidence: rising CO₂ from ice cores and Mauna Loa, global temperature records, sea-level rise, glacier retreat, and ocean acidification. Milankovitch cycles drive natural ice-age pacing.

Ocean basins and features: continental shelf, slope, rise, abyssal plain, mid-ocean ridge, trench, seamount, guyot. Ocean covers ~71% of Earth's surface; average depth ~3.7 km.

Seawater: ~3.5% salinity (35‰), dominated by Na⁺ and Cl⁻; salinity varies with evaporation, precipitation, river input, and ice formation/melting. Density increases with salinity and cold temperature.

Surface currents are wind-driven (gyres, Coriolis, Ekman transport); thermohaline circulation (global conveyor) is driven by density differences and moves heat and nutrients globally.

Tides and waves: tides from gravitational pull of Moon and Sun; wave height depends on wind speed, duration, and fetch; waves break when depth < ~1/2 wavelength.

Coastal processes: longshore drift moves sediment; emergent coasts show wave-cut terraces, submergent coasts show drowned valleys and fjords; groins, jetties, and seawalls alter sediment budgets.

Cryosphere: glaciers, ice sheets (Greenland, Antarctica), sea ice, permafrost, snow. Glacial ice forms from compacted snow; sea ice forms by freezing seawater and excludes salt (brine rejection).

Hydrologic cycle: evaporation, transpiration, condensation, precipitation, infiltration, runoff, groundwater flow. Residence times vary from days (atmosphere) to millennia (deep groundwater, ice).

Groundwater: water table, aquifer (confined vs unconfined), recharge, discharge, springs, wells, artesian conditions. Porosity stores water; permeability transmits it.

Ocean–climate links: oceans absorb CO₂ and heat, buffer temperature, drive El Niño/La Niña (ENSO) via trade-wind and pressure changes, and influence monsoons and hurricane formation.

Inquiry-based instruction: engage, explore, explain, elaborate, evaluate (5E model); students construct explanations from evidence and revise models, aligning with NGSS science and engineering practices.

Lab safety rules: goggles and aprons for chemicals, no eating/drinking, know eyewash and shower locations, report spills, never taste or smell chemicals directly (waft).

Chemical handling: read SDS (Safety Data Sheet) before use; dilute acid by adding acid to water, never water to acid; store acids and bases separately; label all containers.

Equipment safety: use tongs or heat-resistant gloves for hot objects; point test tubes away from people when heating; use a fire blanket or extinguisher for fires, not water on electrical or chemical fires.

Field and specimen safety: rock hammers and goggles for chipping, gloves for handling unknown samples, handwashing after handling soils or rocks, and proper disposal of sharps and broken glass.

Assessment design: align items to standards and cognitive level (Bloom's); use formative checks (exit tickets, concept sketches) and summative tests; rubrics make performance tasks reliable.

Misconceptions to address: seasons from distance to Sun (not tilt), heavier objects sink faster (density not mass), groundwater as underground lakes, and evolution as progress toward humans.

Data literacy: teach graphing (axis labels, scale, trend), unit consistency, and error analysis; students should distinguish correlation from causation and evaluate sources.

Differentiation and safety inclusion: provide adapted tools (large-print maps, tactile models), pre-lab safety contracts, and clear emergency procedures; document safety training and equipment checks.