FTCE Earth/Space Science 008 flashcards

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

Isostasy

The state of gravitational balance in which lithospheric plates float on the denser asthenosphere. Thicker or less dense crust rises higher, which is why continents stand above ocean basins.

Bowen's reaction series

The sequence in which minerals crystallize from cooling magma. Mafic minerals such as olivine form at high temperature, while quartz and potassium feldspar crystallize last at low temperature.

Silicate tetrahedron

A silicon atom bonded to four oxygen atoms, written (SiO4)4-. This unit links into chains, sheets, or frameworks and forms the basis of most crustal rock-forming minerals.

Principle of superposition

In an undisturbed sequence of sedimentary layers, the oldest layer lies at the bottom and the youngest at the top. Deformation must be recognized before applying the rule.

Angular unconformity

An erosion surface separating tilted or folded layers below from flat-lying layers above. It records uplift, deformation, erosion, and later renewed deposition.

Isotope half-life

The time required for half the parent atoms in a sample to decay. After one half-life 50 percent remains, after two 25 percent, and after three 12.5 percent.

Moho

The boundary between Earth's crust and mantle, identified by an abrupt increase in seismic wave velocity. Oceanic crust is thinner, so the Moho sits shallower beneath oceans.

S waves and outer core

Shear waves cannot travel through liquids and are blocked by the outer core, creating a seismic shadow zone. This observation is primary evidence that the outer core is liquid.

Divergent boundary

A plate boundary where plates move apart, producing mid-ocean ridges or continental rift valleys. Magma rises to fill the gap, generating new crust and shallow earthquakes.

Subduction zone

A convergent boundary where denser oceanic lithosphere sinks beneath another plate. It produces deep trenches, volcanic arcs, and the deepest earthquakes.

Seafloor magnetic striping

Symmetrical bands of alternating magnetic polarity on the ocean floor, mirroring the ridge axis. The pattern records reversals of Earth's field as new crust formed.

Moment magnitude scale

An instrumental scale measuring the total energy released by an earthquake. It replaces older magnitude scales and does not vary with distance from the epicenter.

Shield volcano

A broad, gently sloping volcano built from low-viscosity mafic lava that flows far before cooling. Hawaiian volcanoes are classic examples of this landform type.

Chemical weathering

In-place alteration of minerals by water, oxygen, and acids. Hydrolysis converts feldspar to clay, oxidation rusts iron minerals, and dissolution removes soluble rock such as limestone.

Water table

The upper surface of the saturated zone in groundwater. It rises during recharge, falls during drought, and intersects the surface at springs, lakes, and streams.

Coriolis effect

Apparent deflection of moving air or water caused by Earth's rotation. Winds deflect right in the Northern Hemisphere and left in the Southern Hemisphere, shaping global circulation.

Index fossil

A fossil useful for correlation because it is widespread, abundant, and existed for a short geologic time. Its presence narrows the age of the containing layer.

Radiocarbon dating limit

Carbon-14 has a half-life near 5730 years and is practical only for organic remains younger than roughly 50,000 years. Older samples require longer-lived isotope systems.

End-Permian extinction

The largest mass extinction in Earth history, eliminating about 90 percent of marine species. It is linked to Siberian Traps volcanism, warming, and ocean anoxia.

Cambrian explosion

A rapid diversification of animal life about 541 million years ago. It produced most major animal body plans and abundant fossils with hard shells.

Uniformitarianism

The principle that present-day natural processes, operating over long time spans, explain features in the rock record. It provides the basis for interpreting ancient environments.

Faunal succession

The principle that fossil assemblages change in a consistent, recognizable order through layered rocks. This allows correlation of strata across widely separated regions.

Trace fossil

A record of organism activity rather than the body itself, such as footprints, burrows, or feeding trails. Trace fossils indicate behavior and depositional environment.

Kepler's third law

The square of a planet's orbital period equals the cube of its semi-major axis when period is in years and axis in astronomical units. Outer planets therefore orbit more slowly.

Earth's axial tilt

Earth's rotation axis is tilted about 23.5 degrees from perpendicular to its orbital plane. This tilt, not distance from the Sun, causes the seasons.

Solar eclipse

An alignment in which the Moon passes between Earth and the Sun and casts a shadow on Earth. It occurs only at new moon and only near a node of the lunar orbit.

Hertzsprung-Russell diagram

A plot of stellar luminosity against temperature or spectral class. Main-sequence stars form a diagonal band, with giants upper right and white dwarfs lower left.

White dwarf

The remnant core of a low-mass star that has shed its outer layers. It is supported by electron degeneracy pressure and gradually cools over billions of years.

Hubble's law

Galaxies recede from one another at speeds proportional to distance, expressed as v = H0 d. This relationship is key evidence that the universe is expanding.

Cosmic microwave background

Faint microwave radiation filling the universe, released when the early plasma cooled and became transparent. It is relic heat from the Big Bang.

Terrestrial versus Jovian planets

Terrestrial planets are small, dense, rocky, and near the Sun. Jovian planets are large, low-density, gas-rich, ringed, and orbit farther out.

Comet tail direction

A comet's ion and dust tails point away from the Sun because solar wind and radiation pressure push material outward. The tail therefore leads the comet as it departs.

Reflecting telescope

A telescope that uses a curved mirror to gather and focus light. Large mirrors avoid the chromatic aberration of lenses and allow very large apertures.