Praxis Earth and Space Sciences key terms

The state of gravitational balance in which buoyant lithospheric plates float on the denser mantle, adjusting vertically until the weight of each column is supported. Loading by ice or sediment causes subsidence; unloading causes rebound.

Slow circulation of hot, ductile rock driven by heat escaping from Earth's interior, with warm material rising and cooler material sinking. This flow supplies the force that moves lithospheric plates and drives seafloor spreading.

The process in which new oceanic crust forms at mid-ocean ridges as magma rises, cools, and moves away from the ridge on both sides. Magnetic striping and age patterns in the crust record this motion.

The record of Earth's ancient magnetic field preserved in magnetic minerals in rocks. Alternating normal and reversed stripes on the seafloor, symmetric about ridges, provided key evidence for plate tectonics.

The rigid outer shell of Earth, comprising the crust and uppermost mantle, broken into tectonic plates. It behaves elastically over short times and is the layer that subducts, rifts, and deforms at plate boundaries.

A convergent boundary where one lithospheric plate descends beneath another into the mantle. It produces deep ocean trenches, volcanic arcs, and some of the largest and deepest earthquakes.

The three main classes of lithospheric plate margins: divergent, where plates move apart; convergent, where they collide or one subducts; and transform, where they slide past each other. Each produces characteristic landforms and earthquake styles.

A long-lived zone of upwelling mantle heat that melts the overriding plate and builds volcanic chains. As a plate moves over it, successive volcanoes form and age progressively along the chain, as in Hawaii.

Elastic vibrations generated by earthquakes that travel through Earth as body waves (P and S) and surface waves. Their speeds and paths reveal internal layering, and S-wave shadow zones show that the outer core is liquid.

The compositional and mechanical divisions of Earth's interior: crust, mantle, and core compositionally; lithosphere, asthenosphere, mesosphere, outer core, and inner core mechanically. Boundaries are inferred mainly from seismic wave behavior.

The self-sustaining process in which convective motion of electrically conducting liquid iron in the outer core generates Earth's magnetic field. The field protects the atmosphere from solar wind and reverses polarity over geologic time.

The internationally agreed hierarchy of eons, eras, periods, and epochs that divides Earth history, with boundaries defined by major changes in rocks and fossils. It places events in relative order and, where dated, in absolute time.

A method of determining absolute ages by measuring the ratio of a radioactive parent isotope to its stable daughter product and applying the known half-life. Different isotope systems suit different age ranges and materials.

The time required for half of the atoms of a radioactive isotope in a sample to decay. It is constant for each isotope and allows decay ratios to be converted into absolute ages.

A surface in layered rock representing a gap in the record, where erosion removed material or deposition paused before younger layers formed. Its type (angular, disconformity, nonconformity) indicates the missing history.

A fossil species with a wide geographic range but a short geologic lifespan, used to correlate rock layers and assign relative ages. Its presence in separated outcrops indicates the strata formed at about the same time.

The order in which silicate minerals crystallize from cooling magma: olivine and calcium-rich plagioclase first, quartz and potassium feldspar last. It explains mineral associations and the compositions of mafic versus felsic rocks.

The grouping of igneous rocks by composition (felsic to ultramafic) and by texture (coarse-grained intrusive versus fine-grained extrusive). Texture reflects cooling rate and composition reflects magma source and evolution.

The processes that change magma composition, chiefly fractional crystallization, assimilation of wall rock, and magma mixing. These produce a range of rock types from a single parent magma, typically becoming more silica-rich over time.

The breakdown of rock at or near Earth's surface by physical processes such as freeze-thaw and by chemical reactions such as hydrolysis and oxidation. It produces regolith and dissolved ions that erosion later removes.

The removal and transport of weathered material by water, wind, ice, or gravity. It sculpts landscapes, carries sediment downslope, and is distinct from weathering, which merely prepares material for movement.

The laying down of transported sediment when the carrying agent loses energy, as when a river slows or a glacier melts. Deposits record the environment, sorting, and energy of the transporting medium.

The development of soil horizons through weathering of parent material, moderated by climate, organisms, topography, and time. These factors control depth, texture, organic content, and fertility of a soil profile.

A fracture in rock along which displacement has occurred, classified as normal, reverse, or strike-slip according to the direction of relative motion. Faults concentrate earthquakes and may offset or tilt rock layers.

The bending of layered rock under compressional stress, producing anticlines (upward arches) and synclines (downward troughs). Folds record past stress directions and can trap oil, gas, and groundwater.

The volume of water passing a point in a channel per unit time, often expressed in cubic meters per second. Discharge rises downstream and, together with gradient and sediment load, controls erosion and deposition.

The area of land that drains to a common outlet such as a river mouth or lake. Its boundaries follow topographic divides, and its land use and geology determine the water quality downstream.

A permeable rock or sediment unit that stores and transmits enough groundwater to supply wells and springs. Its productivity depends on porosity and permeability, and it can be confined between impermeable layers.

Porosity is the fraction of a material's volume that is open space; permeability is the ability of those spaces to transmit fluid. High porosity alone does not guarantee a good aquifer if pores are poorly connected.

The global deep-ocean overturning driven by differences in temperature and salinity, which set seawater density. Cold, salty water sinks at high latitudes and returns via upwelling, redistributing heat and nutrients worldwide.

The apparent deflection of moving fluids and objects on a rotating Earth, to the right in the Northern Hemisphere and to the left in the Southern. It shapes ocean gyres and global wind belts but does not cause motion.

The rise of cold, nutrient-rich deep water to the surface, often caused by winds moving surface water offshore. It fuels high biological productivity and supports major fisheries along certain coasts.

Organized flows of seawater driven by winds, density differences, and tides, deflected by the Coriolis effect and shaped by coastlines. Surface gyres and deep circulation together move heat between low and high latitudes.

The large-scale circulation pattern of trade winds, westerlies, and polar easterlies, separated by the doldrums and horse latitudes. They arise from unequal heating, pressure gradients, and Coriolis deflection, and steer weather systems.

Large bodies of air sharing temperature and humidity, and the boundaries between them. Cold fronts produce narrow bands of intense storms; warm fronts bring gradual, widespread precipitation.

The formation of organized weather systems such as thunderstorms, tornadoes, and tropical cyclones from instability, moisture, lift, and wind shear. Tropical cyclones require warm ocean water and gain energy from latent heat release.

Energy absorbed or released when water changes phase, without changing temperature. Evaporation stores energy, and condensation in clouds releases it, powering storms and driving much of the atmosphere's circulation.

A remote-sensing tool that detects precipitation intensity and the motion of hydrometeors toward or away from the antenna. Its velocity data reveal rotation within thunderstorms, aiding tornado warnings.

Three rules describing orbital motion: orbits are ellipses with the Sun at one focus; equal areas are swept in equal times; and the square of the orbital period is proportional to the cube of the semi-major axis.

The model in which the Sun and planets formed from a rotating cloud of gas and dust that collapsed, flattened into a disk, and accreted into planetesimals. It explains the coplanar, same-direction orbits and the inner-to-outer composition trend.

The two planetary classes: small, dense, rocky inner worlds (Mercury through Mars) and large, low-density outer giants rich in hydrogen, helium, and ices. Their differences reflect temperature gradients in the early solar nebula.

A plot of stellar luminosity against temperature or spectral class, revealing the main sequence, giants, supergiants, and white dwarfs. It is the central tool for interpreting stellar evolution and distance to star clusters.

The life cycle of a star from nebula to main sequence and beyond, determined mainly by its mass. Low-mass stars end as white dwarfs; massive stars undergo supernovae and leave neutron stars or black holes.

The changing alignment of Earth, Sun, and Moon that produces lunar phases, eclipses, and tides. Eclipses occur only near new or full moon when the orbit's tilt allows alignment; spring tides occur at new and full moon.

The variation in solar energy received at a location over the year, caused mainly by the 23.5-degree tilt of Earth's axis. It drives the seasons and the hemispheric difference in day length and solar angle.

The periodic rise and fall of sea level caused chiefly by the Moon's and Sun's gravitational pull and Earth's rotation. Their range varies with coastal geometry and with lunar phase, producing spring and neap tides.

The exchange of carbon among the atmosphere, oceans, biosphere, soils, and rocks through photosynthesis, respiration, weathering, and volcanism. Human fossil-fuel burning and land-use change have shifted carbon rapidly into the atmosphere.

The trapping of outgoing infrared radiation by atmospheric gases such as water vapor, carbon dioxide, and methane, warming the surface. It makes Earth habitable, and its enhancement by human emissions drives modern climate change.

The set of processes that transform rock among igneous, sedimentary, and metamorphic types through melting, cooling, weathering, burial, and deformation. It links the solid Earth to the hydrosphere and atmosphere over geologic time.

A scale measuring earthquake size from the area of the ruptured fault, the average slip, and rock rigidity. It is more physically meaningful than older magnitude scales for large quakes and is reported as Mw.

An iterative process of observation, hypothesis formation, prediction, and testing against field and laboratory data. Because Earth processes are large and slow, it often relies on comparative studies, modeling, and multiple converging lines of evidence.

Distinguishing whether two measured variables merely vary together or whether one actually produces change in the other. Earth and climate data are often autocorrelated, so apparent correlations require careful causal reasoning and controls.

Reading quantitative Earth science data from plots by identifying axes, units, trends, scales, and anomalies. Candidates must distinguish linear from logarithmic axes and recognize that graph slope and area carry physical meaning.

Low-stakes, ongoing checks of student understanding used to adjust instruction during a unit rather than to assign a grade. In Earth science it can include concept sketches, exit tickets, and prediction tasks about processes.