ILTS Earth and Space Science (241) cheat sheet

Hypothesis: a testable, falsifiable prediction; a theory is a well-tested explanatory framework supported by multiple lines of evidence, not a guess.

Independent variable is manipulated by the researcher; dependent variable is measured; controlled variables are held constant to isolate cause and effect.

Validity means the procedure measures what it claims; reliability means repeated trials give consistent results.

Scientific law describes a consistent relationship (e.g., superposition); a theory explains why it occurs.

Correlation does not establish causation; confounding variables and selection bias are common threats to observational studies.

Measurement error: precision = repeatability of a measurement; accuracy = closeness to the true value; random error scatters, systematic error shifts.

Peer review and replication are the core quality controls of scientific claims; anomalous data must be reported, not discarded.

Scientific models are approximations revised when new evidence conflicts; a single contrary result rarely overturns an established theory.

Earth's layers by composition: crust (mafic oceanic, felsic continental), mantle (ultramafic peridotite), core (iron-nickel); by physical state: lithosphere, asthenosphere, mesosphere, outer core (liquid), inner core (solid).

Bowen's reaction series: olivine, pyroxene, amphibole, biotite crystallize early (high temperature, mafic); quartz, muscovite, K-feldspar crystallize late (felsic).

Igneous textures record cooling rate: coarse phaneritic = slow intrusive cooling; fine aphanitic = rapid extrusive cooling; glassy = quenching; porphyritic = two-stage cooling.

Clastic sedimentary rocks are classified by grain size (gravel, sand, silt, clay); chemical sedimentary rocks (limestone, halite, chert) form by precipitation or evaporation.

Metamorphic grade increases with temperature and pressure; foliation (slate, schist, gneiss) develops under directed stress; nonfoliated examples are quartzite and marble.

Mohs hardness scale 1-10: talc, gypsum, calcite, fluorite, apatite, orthoclase, quartz, topaz, corundum, diamond.

Plate boundaries: divergent (new lithosphere, mid-ocean ridges, rift valleys), convergent (subduction zones, volcanic arcs, fold mountains), transform (strike-slip faults, no lithosphere created or destroyed).

Seafloor magnetic stripes symmetric about ridges and increasing sediment thickness away from ridges support seafloor spreading; hotspots produce age-progressive island chains.

Weathering breaks rock in place (physical: frost wedging, exfoliation; chemical: hydrolysis, oxidation, dissolution); erosion transports the debris; deposition builds landforms.

Stream competence = largest particle size transported; capacity = total sediment load; velocity increases with gradient and discharge.

A stream's base level is the lowest elevation to which it can erode, commonly sea level; graded profiles approach a smooth concave-up curve.

Mass wasting is classified by material and motion: creep, slump, debris flow, rockfall, lahar; water content and slope angle are key controls.

Glacial erosion produces U-shaped valleys, cirques, horns, and striations; deposition produces moraines, drumlins, eskers, and outwash plains.

Karst landscapes form where acidic groundwater dissolves limestone, producing caves, sinkholes, and disappearing streams.

Wind erosion is most effective on fine, dry sediment; deflation, abrasion, and dunes (barchan, transverse, longitudinal) record prevailing wind direction.

Soil horizons: O (organic), A (topsoil), E (eluviation), B (accumulation), C (weathered parent material), R (bedrock).

Relative dating principles: superposition, original horizontality, lateral continuity, cross-cutting relationships, inclusions, and faunal succession.

An unconformity is a gap in the record: angular (tilted beds eroded), disconformity (erosion between parallel beds), nonconformity (sediment over igneous or metamorphic rock).

Radiometric dating: parent decays to daughter at a fixed half-life; after n half-lives, parent fraction = (1/2)^n.

Carbon-14 (half-life ~5,730 years) dates organic material only up to about 50,000 years; uranium-lead and potassium-argon date older rocks and minerals.

Index fossils are widespread, abundant, and short-lived stratigraphically, making them reliable for correlation.

Geologic time scale order: Hadean, Archean, Proterozoic (Precambrian), then Paleozoic, Mesozoic, Cenozoic eras.

Mass extinctions mark era boundaries: end-Permian (~252 Ma, largest), end-Cretaceous (~66 Ma, impact and Deccan volcanism).

Preservation biases: hard parts fossilize far better than soft tissue; marine organisms are overrepresented in the fossil record.

Ocean salinity averages about 35 parts per thousand; evaporation raises it, precipitation and river input lower it.

Surface currents are driven mainly by prevailing winds and deflected by the Coriolis effect (right in the Northern Hemisphere, left in the Southern).

Thermohaline circulation is driven by density differences from temperature and salinity; cold, salty water sinks in high latitudes.

Upwelling brings nutrient-rich deep water to the surface, supporting high biological productivity along western continental margins.

Tides result mainly from the Moon's gravitational pull; spring tides occur at new and full moons, neap tides at quarter moons.

Wavelength, period, and wave speed relate as speed = wavelength / period; waves break when depth is roughly 1.3 times wave height.

The hydrologic cycle: evaporation, transpiration, condensation, precipitation, infiltration, runoff, and groundwater flow.

Groundwater moves from recharge areas to discharge areas; the water table rises and falls with precipitation and pumping.

Atmospheric composition: about 78% nitrogen, 21% oxygen, 0.93% argon, and variable water vapor and carbon dioxide.

Troposphere temperature decreases with altitude; the stratosphere warms with altitude because ozone absorbs ultraviolet radiation.

Air pressure decreases with altitude; standard sea-level pressure is about 1013 mb (29.92 inHg).

Relative humidity is the ratio of actual vapor pressure to saturation vapor pressure; air reaches saturation (dew point) when cooled.

Clouds form when rising air cools adiabatically to saturation; dry adiabatic lapse rate ~10 °C/km, saturated ~6 °C/km.

Mid-latitude cyclones have warm and cold fronts; cold fronts are steeper and produce shorter, more intense precipitation.

The Coriolis effect causes apparent deflection, strongest at the poles and zero at the equator; it does not initiate motion.

Thunderstorms require moisture, instability, and lift; tornado formation is associated with rotating mesocyclones in severe storms.

Terrestrial planets (Mercury, Venus, Earth, Mars) are small, dense, rocky; Jovian planets (Jupiter, Saturn, Uranus, Neptune) are large, low-density, and hydrogen-rich.

Kepler's laws: orbits are ellipses; equal areas are swept in equal times; period squared is proportional to semimajor axis cubed (P^2 = a^3 in AU and years).

Seasons result from Earth's axial tilt (~23.5°), not from distance to the Sun.

Solar system formation: a collapsing nebula flattens into a disk; inner regions are too hot for volatiles, so rocky planets form inside and gas giants outside the frost line.

Main-sequence stars fuse hydrogen into helium in their cores; the Hertzsprung-Russell diagram plots luminosity against temperature.

Moon phases depend on the Sun-Earth-Moon angle; solar eclipses occur at new moon, lunar eclipses at full moon.

The Big Bang is supported by cosmic microwave background radiation, redshift of galaxies, and light-element abundances.

Light-year is a distance (about 9.46 × 10^12 km); apparent magnitude measures brightness, absolute magnitude measures intrinsic luminosity.

Inquiry-based instruction sequences observation, question, hypothesis, investigation, data analysis, and explanation; the teacher facilitates rather than supplies answers.

The 5E model (Engage, Explore, Explain, Elaborate, Evaluate) structures a lesson cycle around student investigation before formal explanation.

Formative assessment (probes, exit tickets, concept maps) guides ongoing instruction; summative assessment measures achievement at the end of a unit.

Rubrics should describe observable performance levels aligned to the targeted standard, not effort or participation.

Misconceptions (e.g., seasons caused by distance to the Sun) persist unless directly confronted with discrepant evidence.

Laboratory safety requires documented procedures, appropriate protective equipment, and supervision of hazardous materials.

English language learners benefit from multimodal representations: diagrams, models, sentence frames, and labeled visuals.

Data literacy tasks should require students to interpret graphs, identify trends, and evaluate whether conclusions follow from evidence.