AEPA Earth Science AZ045 key terms

A testable, tentative explanation for an observed phenomenon that generates predictions which can be checked against evidence. It is narrower than a theory and may be revised or rejected based on results.

The factor in an experiment that the investigator deliberately changes or sets at different levels, so its effect on the measured outcome can be evaluated while other conditions are held constant.

A well-tested, broadly supported explanation for a body of natural phenomena, built from repeated evidence and able to generate new predictions. In science it is not a guess or a casual hunch.

The comparison set in an experiment that receives no treatment or a standard treatment. It shows what would happen without the variable being tested, helping isolate the variable's effect.

A simplified representation, physical, mathematical, or conceptual, of a real system, used to explain observations and make predictions. Models are always approximations and are revised as evidence accumulates.

The unifying theory that Earth's rigid outer shell is broken into plates that move over the weaker mantle, causing earthquakes, volcanoes, mountain building, and the drift of continents over geologic time.

The process where one lithospheric plate descends beneath another at a convergent boundary because it is denser. It creates deep ocean trenches, volcanic arcs, and powerful earthquakes.

A plate margin where two plates move apart and new lithosphere forms from upwelling magma. It produces mid-ocean ridges under oceans and rift valleys on continents.

A plate margin where two plates slide horizontally past each other, neither creating nor destroying lithosphere. The resulting fault friction produces shallow earthquakes, such as along the San Andreas Fault.

The transfer of heat by the movement of a fluid, where warmer, less dense material rises and cooler, denser material sinks. In the mantle it drives plate motion over long timescales.

A naturally occurring, inorganic solid with a definite chemical composition and an ordered internal atomic structure. Minerals are the building blocks of rocks and are identified by properties like hardness and cleavage.

Rock formed when molten material cools and solidifies, either below ground as intrusive rock with large crystals or at the surface as extrusive rock with fine crystals or glass.

Rock formed from compacted and cemented sediments, or from chemical precipitation, typically in layers. It is the main archive of fossils and records past environments.

Rock changed by high heat and pressure without melting, often producing new minerals and a foliated or banded texture. It forms deep within the crust or near magma bodies.

The ongoing set of processes that transform rock among igneous, sedimentary, and metamorphic forms through melting, cooling, weathering, erosion, deposition, burial, and metamorphism. It has no fixed starting point.

Vibrations generated by earthquakes or explosions that travel through Earth. Their differing speeds and paths reveal the planet's internal layered structure.

The point on Earth's surface directly above an earthquake's focus, where seismic waves arrive first and shaking is often strongest. Locating it requires data from at least three seismic stations.

Determining the order of past events without assigning numerical ages, using principles such as superposition and cross-cutting relationships. It establishes sequences but not absolute dates.

The principle that in undisturbed sedimentary rock layers, each layer is older than the one above it and younger than the one below, providing a basis for relative dating.

A fossil of an organism that lived over a wide geographic area but for a short geologic interval, allowing rocks in different places to be correlated and assigned similar ages.

Estimating a rock's age from the ratio of a radioactive parent isotope to its stable daughter product, using the isotope's known half-life. It provides numerical ages for igneous and some metamorphic rocks.

The time required for half of the atoms of a radioactive isotope in a sample to decay. Each isotope has a fixed half-life, making it a reliable clock for radiometric dating.

A gap in the rock record where layers were eroded away or deposition paused before younger rocks formed above. It marks missing time and can be recognized by erosion surfaces.

An event in which a large proportion of species dies out within a geologically short interval. Such events, like the end-Permian and end-Cretaceous, reshape ecosystems and the fossil record.

The standardized division of Earth's 4.6-billion-year history into eons, eras, periods, and epochs, based on major changes recorded in rocks and fossils.

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. It shapes winds and ocean currents but does not cause them.

The global slow overturning of ocean water driven by differences in temperature and salinity, which affect density. It transports heat between latitudes and influences climate.

The fraction of incoming solar radiation reflected by a surface. Bright surfaces like ice and snow have high albedo, while dark oceans and forests absorb more energy.

The warming of a planet's surface as certain atmospheric gases absorb and reemit outgoing infrared radiation. It keeps Earth habitable, and human-added gases intensify it.

A fast, narrow band of strong winds high in the troposphere, driven by temperature contrasts between air masses. It steers weather systems and shifts with the seasons.

A periodic warming of surface waters in the central and eastern equatorial Pacific, coupled with shifts in atmospheric pressure. It disrupts weather patterns worldwide, bringing floods and droughts to different regions.

The total amount of dissolved salts in water, usually expressed in parts per thousand. It affects water density and ocean circulation and varies with evaporation, precipitation, and river input.

The continuous movement of water among oceans, atmosphere, land, and living things through evaporation, transpiration, condensation, precipitation, runoff, and infiltration. It redistributes heat and fresh water around the planet.

The degree to which Earth's orbit departs from a perfect circle, varying on about a 100,000-year cycle. It changes the strength of seasonal differences and modulates ice ages.

The tilt of Earth's rotational axis relative to its orbital plane, currently about 23.5 degrees and varying on a roughly 41,000-year cycle. It controls the severity of seasons.

The slow wobble of Earth's axis, changing the direction it points in space on a cycle of about 26,000 years. It shifts when seasons occur relative to orbital position.

An event in which the Moon passes between Earth and the Sun and blocks sunlight, occurring only near a new moon when the alignment is nearly perfect.

The unusually large tidal range that occurs near new and full moons, when the Sun, Earth, and Moon are nearly aligned and their tidal effects combine.

The changing portion of the Moon's sunlit half visible from Earth as it orbits, cycling from new moon to full moon and back about every 29.5 days.