MTEL Earth and Space Science (74) cheat sheet

Earth's mean radius is about 6,371 km; its mass is about 5.97 × 10^24 kg and its mean density about 5.51 g/cm³ - the densest planet in the solar system.

Earth's interior layers by composition: crust (oceanic basalt ~5–10 km thick, continental granite ~30–70 km), mantle (peridotite, to ~2,900 km depth), outer core (liquid Fe-Ni, S-waves cannot pass), inner core (solid Fe-Ni).

Seismic evidence: P-waves travel through solids and liquids and refract at the core-mantle boundary; S-waves stop at the outer core, proving it is liquid. The Mohorovičić discontinuity marks the crust-mantle boundary.

Plate tectonics: divergent boundaries produce new oceanic crust and rift valleys; convergent boundaries produce subduction zones, trenches, volcanic arcs, and fold mountains; transform boundaries produce strike-slip faults.

Earth's rotation on its axis (west to east) causes the day-night cycle and the apparent daily motion of stars; the ~23.5° axial tilt combined with revolution around the Sun causes the seasons.

Solstices occur when a hemisphere is tilted most toward or away from the Sun (~June 21 and ~December 21); equinoxes (~March 21 and ~September 23) occur when the Sun is over the equator and day and night are nearly equal everywhere.

Relative dating principles: superposition (older below), original horizontality, cross-cutting relationships (a feature cutting another is younger), inclusions, and faunal succession; unconformities represent gaps in the record.

Absolute dating relies on radioactive decay, where the half-life is the time for half the parent isotope to decay; after n half-lives the parent fraction remaining is (1/2)^n. Carbon-14 (half-life ~5,730 years) dates organic material up to ~50,000 years; uranium-lead and potassium-argon date rocks far older.

Earth's magnetic field is generated by convection of liquid iron in the outer core (geodynamo); magnetic reversals recorded in seafloor basalt stripes provide evidence for seafloor spreading.

Kepler's laws: orbits are ellipses with the Sun at one focus; a planet sweeps equal areas in equal times (faster near perihelion); the square of the orbital period is proportional to the cube of the semi-major axis (P² ∝ a³, with P in years and a in AU).

Newton's law of gravitation F = G·m1·m2/r² explains orbital motion; the Sun contains about 99.8% of the solar system's mass, and terrestrial planets are rocky and close to the Sun while Jovian planets are large, gaseous, and distant.

Stellar classification runs OBAFGKM from hottest (~30,000 K+) to coolest (~3,000 K); the Hertzsprung-Russell diagram plots luminosity against temperature and reveals main sequence, giants, and white dwarfs.

The Sun's energy comes from nuclear fusion of hydrogen into helium in its core; energy reaches Earth by radiation through space and is redistributed in the atmosphere and oceans by conduction and convection.

The Big Bang model is supported by the expansion of the universe (redshift), the cosmic microwave background radiation, and the abundance of light elements; Hubble's law states that recession velocity is proportional to distance.

Motions of the Moon: it rotates once per orbit (synchronous rotation), so the same face always points toward Earth; lunar phases arise from the changing angle between Earth, Moon, and Sun, and spring tides occur at new and full moon.

Weather versus climate: weather is short-term atmospheric state; climate is long-term statistical pattern. Unequal solar heating drives pressure gradients, winds, convection, and the Coriolis effect (deflection to the right in the Northern Hemisphere).

Cloud formation requires rising moist air, cooling to the dew point, and condensation nuclei; relative humidity is the ratio of actual vapor to saturation vapor pressure, and air masses form over uniform surfaces and collide along fronts.

The rock cycle links igneous (crystallized from magma or lava), sedimentary (compacted and cemented sediments), and metamorphic (altered by heat and pressure) rocks; weathering, erosion, deposition, and lithification are the sedimentary pathway.

Water and carbon cycles: evaporation, transpiration, condensation, precipitation, and runoff move water; carbon moves among the atmosphere, biosphere, oceans, and lithosphere via photosynthesis, respiration, combustion, and dissolution in seawater.