AEPA Earth Science AZ045 cheat sheet

Hypothesis: a testable, falsifiable prediction; theory: an evidence-supported explanatory framework; law: a widely confirmed regularity often expressed mathematically.

Controlled experiments vary one independent variable, measure a dependent variable, and hold extraneous variables constant to reduce confounding.

Reliability refers to consistency of repeated measurements; validity refers to whether a method measures what it claims to measure.

Accuracy is closeness to an accepted value; precision is repeatability. Random errors scatter measurements; systematic errors shift them consistently.

Correlation alone does not establish causation; causal inference requires controlled manipulation, temporal order, and exclusion of alternatives.

Sample size and representative sampling affect generalizability; anecdotal evidence and single observations carry little inferential weight.

Peer review and replication are core safeguards: independent repetition with consistent results strengthens confidence in a claim.

Scientific notation: a × 10^n, where 1 ≤ |a| < 10; significant figures reflect measurement precision, not exact counting numbers.

Igneous rock classification depends on texture (intrusive coarse-grained vs extrusive fine-grained) and composition (mafic vs felsic).

Sedimentary rocks form by compaction and cementation of sediments or precipitation; they commonly preserve fossils and sedimentary structures.

Metamorphic rocks form by heat and pressure; foliation develops under directed stress, while nonfoliated textures indicate uniform conditions.

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

Divergent boundaries create crust; convergent boundaries destroy or thicken crust; transform boundaries slide horizontally.

P-waves arrive first and travel through solids and liquids; S-waves arrive later and cannot travel through liquids.

Earth's layers by composition: crust, mantle, core; by physical properties: lithosphere, asthenosphere, mesosphere, outer core, inner core.

Magnetic reversals recorded in oceanic crust form symmetrical stripes around mid-ocean ridges, supporting seafloor spreading.

Hot spots produce chains of volcanoes as plates move over a fixed mantle plume, such as the Hawaiian Islands.

Principle of superposition: in undisturbed sequences, older layers are below younger layers.

Original horizontality: sedimentary layers form near horizontal; later tilting or folding indicates deformation.

Cross-cutting relationships: faults and intrusions are younger than the rocks they cut.

Inclusions: fragments inside a rock are older than the rock containing them.

Unconformities mark missing time: angular unconformity, nonconformity, and disconformity.

Faunal succession: fossil assemblages change in a consistent order, allowing correlation of rock layers.

Radiometric age formula: N = N0(1/2)^(t/T), where T is half-life; parent decreases while daughter accumulates.

Index fossils are widespread, short-lived species useful for relative dating; absolute ages require radiometric methods.

Mass extinctions mark boundaries in the geologic time scale and are associated with major environmental change.

Weather is short-term atmospheric state; climate is long-term statistical pattern, typically 30 years or more.

Atmospheric layers from surface upward: troposphere, stratosphere, mesosphere, thermosphere, exosphere.

Temperature generally decreases with altitude in the troposphere; ozone absorption warms the stratosphere.

Air pressure decreases with altitude; wind flows from high pressure to low pressure and is deflected by the Coriolis effect.

Relative humidity compares water vapor content to saturation capacity; dew point is the temperature at saturation.

Ocean surface currents are driven mainly by winds and deflected by Coriolis; gyres circulate clockwise in the Northern Hemisphere.

Thermohaline circulation is density-driven: cold, salty water sinks and deep currents return nutrients and heat globally.

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

Greenhouse gases absorb and re-emit infrared radiation; increasing concentrations raise average surface temperature.

Earth rotates west-to-east once per day, causing day/night and apparent motion of celestial objects.

Earth revolves around the Sun once per year; axial tilt of about 23.5° causes seasons, not distance from the Sun.

Moon phases depend on the Sun-Moon-Earth angle; one complete cycle takes about 29.5 days.

Solar eclipses occur at new moon when the Moon passes between Earth and Sun; lunar eclipses occur at full moon.

Spring tides occur at new and full moons; neap tides occur at quarter moons.

Kepler's laws: orbits are ellipses; equal areas in equal times; P^2 ∝ a^3 for bodies orbiting the same mass.

Newton's law of gravitation: F = G(m1m2/r^2), determining orbital motion and weight.

A light-year is the distance light travels in one year, about 9.46 × 10^12 km; it measures distance, not time.

Main sequence stars fuse hydrogen into helium; their position on the H-R diagram depends on luminosity and temperature.