OSAT Earth Science (OK108) key terms

A systematic process of asking testable questions, gathering evidence through observation and measurement, forming explanations, and revising them as new data appear. It emphasizes evidence over authority and repeatability over anecdote.

Evaluating a proposed explanation by deriving predictions that could fail if the explanation is wrong, then checking those predictions against collected data. A hypothesis that survives repeated attempts at refutation gains support but is never proven absolutely.

Information obtained through direct observation, measurement, or experiment rather than reasoning alone. In Earth science it often comes from field measurements, drill cores, seismic records, and satellite data that others can reexamine.

The principle that the same physical, chemical, and biological processes operating today also operated in the geologic past, so present-day processes can be used to interpret ancient rocks. It does not assume rates were always constant.

The standardized hierarchy of eons, eras, periods, and epochs used to organize Earth history, with boundaries drawn mainly at major changes in fossils and rock sequences and dated radiometrically. Its divisions are internationally agreed conventions.

Determining the order of past events without assigning numerical ages, using principles such as superposition, original horizontality, cross-cutting relationships, and inclusions. It establishes sequence, not absolute age.

A fossil species with a wide geographic range and a short stratigraphic lifespan, making it useful for correlating rock layers between regions. Its presence signals a narrow interval of geologic time.

The theory that Earth's rigid outer shell is broken into plates that move over a weaker layer, driven largely by convection and slab pull. It explains earthquakes, volcanoes, mountain belts, and the distribution of fossils and rock types.

The process in which new oceanic lithosphere forms at mid-ocean ridges as magma rises, cools, and moves away from the ridge axis. Magnetic stripe patterns and increasing sediment thickness away from ridges record this motion.

The record of ancient magnetic field direction and strength preserved in magnetic minerals within rocks. Reversals recorded in oceanic crust as mirror-image stripes on either side of ridges provided key evidence for seafloor spreading.

A convergent boundary where one lithospheric plate descends beneath another, producing deep ocean trenches, volcanic arcs, and frequent large earthquakes. The downgoing slab also drives much of the plate motion through slab pull.

The condition in which lighter crustal blocks float in gravitational balance on the denser mantle, so thicker or less dense crust rides higher. Loading by ice or sediment causes slow vertical adjustment until balance is restored.

Elastic energy traveling through Earth as body waves (P and S) or surface waves. Their speeds and paths change with material properties, so their arrival times reveal internal layering and the liquid state of the outer core.

The boundary separating the crust from the mantle, marked by an abrupt increase in seismic wave speed. It lies at roughly 5 to 10 kilometers depth beneath oceans and 30 to 50 kilometers beneath continents.

The compositional divisions of Earth into crust, mantle, and core, with the core split into liquid outer and solid inner parts. A separate mechanical classification distinguishes lithosphere, asthenosphere, mesosphere, and core.

A naturally occurring, inorganic solid with a definite chemical composition or range and an ordered internal atomic structure, usually forming crystals. Its diagnostic properties include hardness, cleavage, luster, streak, and crystal form.

A relative ranking from 1 (talc) to 10 (diamond) of how easily minerals are scratched, based on which minerals scratch which. It is ordinal, not proportional, so diamond is far harder than its rank suggests.

The tendency of a mineral to break along flat planes determined by weak bonds in its atomic structure. The number and angles of cleavage directions help identify minerals such as halite, calcite, and micas.

Rock formed by cooling and crystallization of magma or lava. Slow cooling underground produces coarse-grained intrusive rocks such as granite, while rapid cooling at the surface produces fine-grained extrusive rocks such as basalt.

Rock formed from weathered debris, chemical precipitates, or organic remains that are deposited, compacted, and cemented. Layering, fossils, and grain features make sedimentary rocks the main archive of past environments.

Rock whose mineral composition or texture changed in the solid state under high temperature, pressure, or chemically active fluids. Foliation and index minerals record the intensity of metamorphism.

The set of processes that transform material among igneous, sedimentary, and metamorphic states through melting, crystallization, weathering, erosion, deposition, burial, and metamorphism. Plate tectonics and the water cycle supply its energy and transport.

The in-place breakdown of rock by physical, chemical, or biological processes without transporting the debris. Frost wedging, hydrolysis, and root action are common agents, and climate strongly controls which dominates.

The removal and transport of weathered material by water, wind, ice, or gravity. It shapes landforms and, together with deposition, redistributes sediment from uplands to basins and coasts.

The laying down of transported sediment when the transporting agent loses energy, for example where a river slows or a glacier melts. Depositional features include deltas, sandbars, moraines, and alluvial fans.

A vertical sequence of soil horizons from surface litter to unweathered parent material, typically labeled O, A, E, B, C, and R. Horizon development reflects climate, organisms, relief, parent material, and time.

The continuous movement of water among oceans, atmosphere, land, and living things through evaporation, transpiration, condensation, precipitation, infiltration, runoff, and groundwater flow. Solar energy and gravity drive the circulation.

A body of rock or sediment that stores and transmits groundwater in usable quantities. Porosity determines how much water it holds, while permeability determines how readily water moves through it.

The land area whose runoff drains to a common stream, river, lake, or ocean outlet, bounded by topographic divides. Watershed boundaries are defined by elevation, not political lines, and control downstream water quality.

The slow upward adjustment of the crust after the weight of an ice sheet is removed, continuing for thousands of years after deglaciation. It is a visible demonstration of isostatic compensation and affects regional sea level.

The apparent deflection of moving air or water caused by Earth's rotation, to the right in the Northern Hemisphere and to the left in the Southern. It grows with latitude and speed and shapes global wind belts and storm rotation.

The change in atmospheric pressure over distance, which drives air from higher toward lower pressure. The Coriolis effect turns that flow, producing geostrophic winds nearly parallel to isobars aloft.

The warming of a planet's surface because certain atmospheric gases absorb and re-emit outgoing infrared radiation. Water vapor, carbon dioxide, methane, and nitrous oxide are the principal terrestrial contributors.

The fraction of incoming solar radiation reflected by a surface, ranging from near 0 for dark oceans to over 0.8 for fresh snow. Changes in ice cover and cloudiness alter albedo and feed back into climate.

A persistent, large-scale movement of seawater driven by winds, density differences, and Earth's rotation. Surface currents redistribute heat between low and high latitudes, while deep currents overturn slowly on millennial timescales.

The gravitational and geometric relationships among Earth, its Moon, and the Sun that produce day and night, seasons, tides, moon phases, and eclipses. Axial tilt, not distance, causes the seasons.

The regular rise and fall of sea level caused mainly by the Moon's gravitational pull and Earth's rotation, modulated by the Sun. Spring tides occur at new and full moon; neap tides at quarter phases.

The alignment of Sun, Earth, and Moon that produces solar or lunar eclipses. Solar eclipses require the Moon between Sun and Earth at new moon; lunar eclipses require Earth between them at full moon, near a node.

The set of practices that prevent injury and contamination in hands-on science work, including hazard review, personal protective equipment, proper chemical storage, waste handling, and clear emergency procedures. It must be planned before any activity begins.