MTEL Earth and Space Science (74) flashcards

33 cards. Read the term and the definition here. The deck at the top of this page is optional.

Earth's mean radius

About 6,371 km from center to surface. This value is used to scale models of Earth's interior and to compare Earth with other planets.

Outer core composition

Liquid iron and nickel. Convection in this layer generates Earth's magnetic field and blocks S-waves, which cannot travel through liquids.

S-wave shadow zone

A region where S-waves are not detected because they cannot pass through the liquid outer core. It provides evidence that the outer core is fluid.

Divergent plate boundary

A boundary where plates move apart and new oceanic crust forms, as at mid-ocean ridges. Associated features include rift valleys, seafloor spreading, and shallow earthquakes.

Subduction zone

A convergent boundary where a denser oceanic plate sinks beneath another plate. It produces deep ocean trenches, volcanic arcs, and deep-focus earthquakes.

Transform boundary

A boundary where plates slide horizontally past each other. Crust is neither created nor destroyed, and strike-slip faults such as the San Andreas generate earthquakes.

Principle of superposition

In an undisturbed sequence of sedimentary rocks, each layer is older than the one above it and younger than the one below. This supports relative dating.

Cross-cutting relationships

A geologic feature that cuts across another is younger than the feature it cuts. Faults, dikes, and intrusions are dated this way relative to surrounding rock.

Half-life

The time required for half of a radioactive parent isotope to decay. After n half-lives, the remaining parent fraction equals one-half raised to the n power.

Carbon-14 dating

Uses carbon-14's roughly 5,730-year half-life to date organic remains up to about 50,000 years old. It is unsuitable for dating most igneous rocks.

Cause of the seasons

Earth's approximately 23.5-degree axial tilt combined with its revolution around the Sun. The tilt changes the angle and duration of sunlight through the year.

Equinox

Occurs around March 21 and September 23, when the Sun is directly over the equator. Day and night are nearly equal in length everywhere on Earth.

Geodynamo

The process by which convection of liquid iron in Earth's outer core generates the magnetic field. Reversals recorded in seafloor basalt support seafloor spreading.

Kepler's third law

The square of a planet's orbital period is proportional to the cube of its semi-major axis. In units of years and astronomical units, the relation is P squared equals a cubed.

Kepler's second law

A line from the Sun to a planet sweeps out equal areas in equal times. A planet therefore moves faster near perihelion and slower near aphelion.

Newton's law of gravitation

The gravitational force between two masses equals the gravitational constant times the product of the masses divided by the square of the distance between them.

Terrestrial versus Jovian planets

Terrestrial planets are small, rocky, dense, and near the Sun. Jovian planets are large, gaseous or icy, low density, and orbit beyond the asteroid belt.

Hertzsprung-Russell diagram

A plot of stellar luminosity against temperature or spectral class. It organizes stars into the main sequence, giants, supergiants, and white dwarfs.

Spectral classes OBAFGKM

A stellar temperature sequence from hottest to coolest, roughly 30,000 K down to 3,000 K. The Sun is a G-type main-sequence star.

Solar energy source

Nuclear fusion of hydrogen into helium in the Sun's core. The energy is released as radiation and reaches Earth across space without a medium.

Evidence for the Big Bang

Expansion of the universe shown by redshift, the cosmic microwave background radiation, and the observed abundance of light elements such as hydrogen and helium.

Hubble's law

The farther a galaxy is from Earth, the faster it appears to recede, with velocity proportional to distance. This supports an expanding universe.

Synchronous rotation of Moon

The Moon rotates once per orbital revolution, so the same face always points toward Earth. This results from tidal locking over geologic time.

Cause of lunar phases

The changing angle between Earth, the Moon, and the Sun. Half the Moon is always lit, but observers see varying portions of the lit side.

Spring tide

Occurs at new and full moon when the Sun and Moon align, adding their tidal forces. This produces the greatest tidal range.

Coriolis effect

The apparent deflection of moving air or water caused by Earth's rotation. It deflects motion to the right in the Northern Hemisphere and to the left in the Southern.

Weather versus climate

Weather is the short-term state of the atmosphere. Climate is the long-term average and variability of weather over decades or more.

Dew point

The temperature to which air must cool at constant pressure to reach saturation. Cooling below the dew point produces condensation and cloud droplets.

Relative humidity

The ratio of the actual water vapor in air to the maximum vapor the air could hold at that temperature, usually expressed as a percentage.

Rock cycle

The set of processes that transform igneous, sedimentary, and metamorphic rocks through melting, cooling, weathering, erosion, deposition, compaction, and metamorphism.

Igneous rock formation

Crystallization of molten material. Intrusive rocks cool slowly underground and are coarse-grained; extrusive rocks cool quickly at the surface and are fine-grained.

Metamorphic rock

Rock altered by heat and pressure without melting. Foliation and mineral recrystallization are common, as in slate, schist, and gneiss.

Water cycle processes

Evaporation, transpiration, condensation, precipitation, infiltration, and runoff. Solar energy drives the cycle, and gravity moves water downhill and underground.