Universe, Solar System & Earth Systems – Vocabulary Review

Vocabulary flashcards covering cosmology, solar-system formation, Earth structure, atmosphere, hydrosphere, biosphere, and related scientific terms to aid exam preparation.

Creation Myth

A culture’s symbolic narrative describing the beginning of the world (e.g., the six-day Genesis account).

Big Bang Theory

Model proposed by Alexander Friedmann & Georges Lemaître describing a hot, dense origin of the universe that has expanded ever since.

Big Bang Singularity

The initial state of “nothingness” in which space, time, matter and energy were infinitely compressed.

Inflation (Cosmology)

A brief period of extremely rapid expansion immediately after the Big Bang, enlarging the universe from sub-atomic size.

Nucleosynthesis

Early Big-Bang process in which protons and neutrons fused to form light nuclei such as hydrogen and helium.

Recombination

Epoch when electrons bonded with nuclei to form neutral atoms, allowing photons to travel freely and ending the cosmic “Dark Ages.”

Inflationary Epoch

Stage when the universe grew from the size of an atomic nucleus to macroscopic proportions in a fraction of a second.

Radiation Era

Period dominated by photons; origin of the cosmic microwave background radiation.

Matter Domination

Era when matter (rather than radiation) controlled cosmic dynamics and lithium atoms first formed.

Strong Nuclear Force

Short-range, attractive force that binds protons and neutrons in atomic nuclei.

Electromagnetic Force

Long-range force of attraction or repulsion between charged particles; binds atoms.

Weak Nuclear Force

Short-range interaction responsible for radioactive decay and neutrino production.

Gravitational Force

Weak, long-range attractive force that governs the motion of planets, stars, and galaxies.

Cosmic Microwave Background (CMB)

Faint, uniform microwave radiation discovered by Penzias & Wilson, viewed as the afterglow of the Big Bang.

Hubble’s Law

Observation that galaxies are moving away from each other, implying universal expansion.

Light-Element Abundance

High proportions of H, He (and traces of Li, Be) predicted and observed as evidence for Big-Bang nucleosynthesis.

Descartes’ Vortex Theory

Early solar-system model in which whirlpool-like motions in a primordial fluid formed planets and satellites.

Buffon’s Collision Theory

Hypothesis that planets condensed from material pulled off the Sun by a passing comet.

Kant-Laplace Nebular Theory

Proposal that the solar system formed from a rotating gas-dust nebula collapsing under gravity.

Jeans-Jeffreys Tidal Theory

Idea that tidal forces ripped material from the Sun, which later condensed into planets.

Solar Nebular Theory

Modern model where interstellar gas and dust condensed into planetesimals, protoplanets, and finally the Sun and planets.

Planetesimal

Kilometer-scale body formed by dust collisions in the solar nebula; building block of planets.

Protoplanet

Large, gravitationally bound aggregation of planetesimals in the early solar system.

Cold Accretion Hypothesis

Concept that protoplanets formed from cool material gradually sticking together without initial melting.

Solar Wind

Stream of charged particles emitted by the young Sun, affecting planetary atmospheres and dust.

Terrestrial Planet

Inner, rocky planet composed mainly of silicate rock and metals (Mercury, Venus, Earth, Mars).

Jovian Planet

Outer gas-giant planet composed chiefly of hydrogen and helium (Jupiter, Saturn, Uranus, Neptune).

Dwarf Planet

Celestial body orbiting the Sun, massive enough for self-gravity to be spherical, but not having cleared its orbital neighborhood (e.g., Pluto).

International Astronomical Union (IAU)

Body that defines planetary nomenclature and classification standards.

Asteroid

Small, rocky, airless body orbiting the Sun; also called a minor planet.

Main Asteroid Belt

Region between Mars and Jupiter containing most known asteroids.

Near-Earth Asteroid (NEA)

Asteroid whose orbit brings it close to Earth, monitored for potential impact hazards.

Ceres

First discovered asteroid and also classified as a dwarf planet within the main belt.

Comet

Icy body that develops a glowing coma and tail when near the Sun due to sublimation of volatiles.

Kuiper Belt

Disc-shaped region beyond Neptune containing short-period comets and icy bodies; the solar system’s ‘final frontier.’

Oort Cloud

Hypothetical distant spherical shell of icy objects believed to be the source of long-period comets.

Accretion (Earth Formation)

Growth of Earth by gradual accumulation of centimeter-sized dust and kilometer-sized planetesimals.

Differentiation (Planetary)

Process where denser materials (Fe, Ni) sink to a planet’s core while lighter materials rise to form crust.

Inge Lehmann

Seismologist who discovered Earth’s solid inner core, identifying the Lehmann discontinuity.

Inner Core

Solid, metallic (Fe-Ni) central sphere of Earth with an estimated radius of ~1250 km.

Outer Core

Liquid Fe-Ni layer (~2300 km thick) whose convection generates Earth’s magnetic field.

Gutenberg Discontinuity

Boundary between Earth’s lower mantle and outer core marked by seismic wave changes.

Mohorovičić Discontinuity (Moho)

Seismic boundary separating Earth’s crust from the upper mantle.

Asthenosphere

Ductile, partially molten upper-mantle layer beneath the lithosphere that enables plate motion.

Lithosphere

Rigid outer shell of Earth comprising crust and uppermost mantle, broken into tectonic plates.

Plate Tectonic Theory

Framework explaining large-scale movement of lithospheric plates over the asthenosphere.

Pangaea

Supercontinent that existed during the late Paleozoic and early Mesozoic eras.

Divergent Boundary

Tectonic boundary where plates move apart, creating new crust (e.g., mid-ocean ridges).

Convergent Boundary

Tectonic boundary where plates collide, often forming mountains or subduction zones.

Transform Boundary

Plate boundary where plates slide horizontally past one another (e.g., San Andreas Fault).

Troposphere

Lowest atmospheric layer (surface to ~12 km) where weather occurs and temperature decreases with altitude.

Tropopause

Boundary between troposphere and stratosphere where temperature lapse rate stops.

Stratosphere

Atmospheric layer (12–50 km) where temperature rises with altitude due to ozone absorption.

Mesosphere

Middle layer (50–80 km) with decreasing temperature; meteors burn here.

Thermosphere

Upper layer (80–700 km) with rising temperatures; contains the ionosphere.

Ionosphere

Region of ionized gases within the thermosphere important for radio communication.

Exosphere

Outermost, thin atmospheric layer (above ~700 km) merging into space; hosts satellites.

Photodissociation

Splitting of water vapor by UV radiation, releasing oxygen in early atmosphere evolution.

Cyanobacteria

Photosynthetic microbes that produced Earth’s first significant oxygen via CO₂ + H₂O → glucose + O₂.

Hydrosphere

All of Earth’s water in liquid, solid, and vapor states, including oceans, lakes, and groundwater.

Salinity

Concentration of dissolved salts in water, expressed in parts per thousand (ppt).

Epipelagic Zone

Sunlit ocean layer (0–200 m) supporting most photosynthetic life.

Mesopelagic Zone

‘Twilight’ ocean layer (200–1000 m) with dim light and many migrating organisms.

Bathypelagic Zone

Midnight zone (~1000–4000 m) of total darkness and high pressure.

Abyssopelagic Zone

Deep-sea zone (4000–6000 m) of near-freezing waters and sparse life.

Hadalpelagic Zone

Deepest ocean trenches (>6000 m) hosting specialized organisms like tube worms.

Biosphere

Global sum of all ecosystems; the zone of life on Earth.

Edward Suess

Austrian geologist who coined the term “biosphere” in 1875.

Biota

The collective living organisms within the biosphere.

Gaia Hypothesis

Concept proposing Earth functions as a self-regulating, quasi-living system.

Climate

Long-term average of weather patterns in a region.

Biome

Major ecological community defined by climate and dominant vegetation.

Aquatic Biome

Biome encompassing freshwater and marine environments.

Desert Biome

Ecosystem with ≤50 cm annual rainfall, extreme temperatures, and drought-adapted life.

Taiga

Boreal forest biome with coniferous trees, long cold winters, and short summers.

Estuary

Partially enclosed coastal body where freshwater mixes with seawater, creating rich ecosystems.

Photic Zone

Upper ocean layer receiving sufficient light for photosynthesis.

Aphotic Zone

Ocean depths lacking enough light for photosynthesis.

Freshwater Ecosystem

Aquatic system of rivers, streams, lakes, ponds, or wetlands with low salinity.

Chaparral

Minor biome characterized by hot, dry summers and cool, moist winters; dominated by shrubs.