OSAT Earth Science (OK108) flashcards

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

Hypothesis

A testable, falsifiable explanation for an observation that generates predictions; it becomes a theory only after repeated confirmation by independent evidence.

Density formula

Density equals mass divided by volume, usually in grams per cubic centimeter; it identifies minerals and explains why dense oceanic crust subducts beneath lighter continental crust.

Radiometric dating

Method using the known decay rate of a radioactive isotope to calculate a rock's numeric age; parent-to-daughter ratios and half-life determine the result.

Axial tilt

Earth's axis is tilted about 23.5 degrees from perpendicular to its orbital plane, causing seasons as each hemisphere leans toward or away from the Sun.

Spring tides

Unusually high and low tides that occur at new and full moons, when the Sun, Earth, and Moon align and their gravitational effects combine.

Solar eclipse

An event in which the Moon passes between Earth and the Sun, blocking sunlight; it can occur only at new moon when the alignment is nearly perfect.

Kepler's third law

The square of a planet's orbital period is proportional to the cube of its average distance from the Sun, linking distance to orbital speed.

Mineral definition

A naturally occurring, inorganic solid with an ordered crystalline structure and a definite chemical composition or limited range of compositions.

Mohs hardness scale

A relative ranking from talc (1) to diamond (10) in which a harder mineral scratches a softer one; it is ordinal, not a proportional measure of hardness.

Bowen's reaction series

The sequence in which silicate minerals crystallize from cooling magma, from olivine and calcium feldspar at high temperature to quartz and muscovite at low temperature.

Foliated metamorphic rock

A metamorphic rock with parallel mineral alignment produced by directed pressure; examples include slate, phyllite, schist, and gneiss, formed in increasing grade.

Clastic sedimentary rock

Rock made of weathered fragments cemented together, classified by grain size: conglomerate, sandstone, siltstone, and shale from coarsest to finest.

Seafloor spreading

The process by which new oceanic crust forms at mid-ocean ridges and moves away, recorded by symmetric magnetic striping and increasing crustal age.

Subduction zone

A convergent boundary where one lithospheric plate descends beneath another, producing trenches, volcanic arcs, and deep earthquakes.

Normal fault

A fault caused by tensional stress in which the hanging wall moves down relative to the footwall, typical of divergent boundaries and continental rifts.

Anticline

A fold that arches upward, with the oldest exposed rocks in its core and layers dipping away from the axis on both sides.

S-wave shadow zone

The region where shear waves are not detected because they cannot travel through liquid; its pattern provides evidence that the outer core is liquid.

Chemical weathering

The breakdown of rock by chemical reactions such as hydrolysis, oxidation, and dissolution, commonly producing clay minerals and dissolved ions.

Soil horizons

Vertical layers in a soil profile: O organic matter, A topsoil, E leached layer, B subsoil, C weathered parent material, and R bedrock.

Mass wasting

Downslope movement of rock and soil under gravity, classified by material and motion as creep, slump, debris flow, or rockfall.

Karst topography

Landscape formed by dissolution of limestone, featuring caves, sinkholes, disappearing streams, and poor surface drainage.

Principle of superposition

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

Index fossil

A fossil of an organism that lived over a short time span but was widespread and abundant, making it useful for correlating rock layers.

K-Pg extinction

The mass extinction about 66 million years ago, likely caused by an asteroid impact, that ended the dinosaurs and many marine species.

Unconformity

A surface representing a gap in the geologic record where erosion or nondeposition removed rock layers before younger sediments were deposited.

Coriolis effect

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

Cold front

The boundary where a cold air mass pushes under warm air, producing steep uplift, rapid cooling, and often brief intense thunderstorms.

Rain shadow

A dry region on the leeward side of a mountain range, where descending air has lost moisture after rising and cooling on the windward side.

Thermohaline circulation

A slow global ocean circulation driven by differences in temperature and salinity, moving heat and nutrients between ocean basins.

Longshore drift

The movement of sediment along a coast by waves approaching at an angle, then returning straight back to the sea.

Aquifer

A permeable rock or sediment body that stores and transmits enough groundwater to supply wells or springs.

Formative assessment

Ongoing, low-stakes checks of student understanding during instruction, used to adjust teaching rather than to assign a final grade.