Earth science

Fumarole: volcanic gas vents and their geology Fumarole A fumarole is an opening in the Earth's crust that emits steam and volcanic gases. This article explains composition, formation, hazards, uses, and how fumaroles differ from relate…

Future of the Earth: Physical drivers, timelines, and likely outcomes Future of the Earth An overview of the long-term physical, geological, and biological factors that will shape Earth's future — from orbital cycles and plate tectonics to solar evolution and the eventu…

Gabbro: coarse-grained intrusive rock of the oceanic crust and rift zones Gabbro Gabbro is a dark, coarse-grained intrusive igneous rock chemically similar to basalt, common in oceanic crust and rift-related intrusions; it records magmatic processes and has pra…

Gaia hypothesis The Gaia hypothesis proposes that life and Earth's nonliving components form an interacting, self-regulating system that helps maintain conditions suitable for life, proposed by Ja…

Gale (meteorology) Gale A gale is a very strong sustained wind. This article explains definitions, measurement scales (Beaufort), typical speeds, impacts at sea and on land, warnings, and how gales differ…

Galena (lead sulfide) Galena Galena is a common sulfide mineral (PbS) and the principal ore of lead; notable for its metallic luster, cubic crystals, and associations with minerals like sphalerite and calcite.

Gangue: Waste Material in Ore Processing Gangue Gangue is the non-valuable mineral matter associated with ore. This article explains its nature, common minerals, role in extraction and processing, environmental issues, and how s…

Garibaldi Volcanic Belt: geology, eruptions, hazards and regional significance Garibaldi Volcanic Belt Northern segment of the Cascade volcanic arc in southwestern British Columbia. Stratovolcanoes formed by subduction, notable vents, eruptive history, hazards, monitoring and region…

Gemology: The Science and Practice of Gem Identification and Appraisal Gemology Gemology is the study of gemstones—their physical and chemical properties, origins, treatments, and identification methods used for grading, authentication, and responsible trade.

Geochronology: methods and applications for dating Earth materials Geochronology Geochronology establishes the ages and temporal relationships of rocks, sediments, fossils and planetary materials using relative and absolute dating methods and laboratory techniq…

Geoid: Earth's equipotential surface and its role in geodesy Geoid The geoid is the equipotential surface of Earth's gravity field that best fits global mean sea level. It serves as the physical reference for heights and is measured by gravimetry,…

Geologic time scale: organizing Earth's deep history Geologic time scale Comprehensive overview of the geologic time scale: methods (stratigraphy, fossils, radiometric dating), major divisions and boundaries, key events, history of its development and p…

Geological formation (lithostratigraphic unit) Geological formation A geological formation is a mappable, lithologically distinct body of rock used in lithostratigraphy to describe, correlate and interpret Earth's layered rock record across regions…

Geological map — definition, components, history and uses Geological map A geological map displays the distribution, composition and structure of rock units and geologic features at Earth's surface. Covers map elements, production methods, history, map…

Geology: study of Earth's materials, processes, and history Geology Geology examines Earth's solid materials, structures and processes — rocks, minerals, tectonics, and the events that shape planetary history and resources.

Geomagnetic reversal A geomagnetic reversal is when a planet's magnetic field flips polarity. This article explains causes, evidence, timing, effects, and how reversals are distinguished from brief exc…

Geomorphology: study of landforms and surface processes Geomorphology Scientific study of landforms, the processes that shape them, and landscape evolution. Combines field observation, experiments and modeling; informs hazard assessment, planning, an…

Geophone: seismic ground-motion sensor Geophone A geophone is a ground-motion sensor that converts Earth vibrations into electrical signals. Used in seismology, exploration and engineering to record and analyze wave motion, timi…

Geophysical Fluid Dynamics Laboratory (GFDL) Geophysical Fluid Dynamics Laboratory NOAA research laboratory specializing in atmosphere and ocean dynamics, numerical climate and earth‑system modeling, and the development of tools for weather and climate prediction…

Geophysics: study of the physical Earth, its structure and environment Geophysics Geophysics applies physics to study Earth's interior, surface and space environment. It covers seismic, gravitational, magnetic, electrical and thermal observations used to underst…

Geothermal energy: heat from the Earth — uses, methods, and prospects Geothermal energy Geothermal energy is heat from beneath the Earth's surface used for electricity, heating and cooling. This article explains resources, plant types, direct uses, heat pumps, history…

Geyser: erupting hot springs and how they form Geyser Geysers are rare hot springs that periodically eject water and steam. This article explains their formation, types, global distribution, scientific importance, and safety considera…

Gibbsite — aluminium hydroxide mineral (Al(OH)3) Gibbsite Gibbsite (Al(OH)3) is a naturally occurring aluminium hydroxide mineral, a primary component of bauxite and a key intermediate in industrial alumina production and geologic weather…

Lakes formed by glaciers (glacial lakes) Glacial lake Bodies of water that occupy depressions carved or dammed by glaciers. They form when ice melts and water fills hollows; types include cirque, moraine-dammed, kettle and ribbon lake…

Glaciation: formation, types, effects, and climate role Glaciation Glaciation is the growth and movement of land ice. This article explains how glaciers form, the landforms they leave, their climate role, and the orbital cycles that drive ice ages…

Glacier: formation, types, features, and contemporary significance Glacier A glacier is a persistent mass of compacted snow and ice that flows under its own weight, shaping landscapes and storing much of Earth's freshwater. This article explains formation…

Glaciology: the science of glaciers, ice sheets, and frozen ground Glaciology Glaciology is the scientific study of glaciers, ice sheets, sea ice and frozen ground, their physical processes, histories and impacts on climate, sea level, water resources and la…

Global cooling (climate hypothesis and context) Global cooling The idea, prominent in some 1960s–1970s media, that Earth’s surface temperatures would fall for decades. It was never a sustained scientific consensus; later evidence and models sh…

Global warming: causes, effects, history and responses Global warming Global warming is the long-term rise in Earth’s average temperature driven mainly by human activities. This article explains causes, mechanisms, impacts, and approaches to mitigati…

Gneiss: Layered Metamorphic Rock — Formation, Types, and Uses Gneiss Gneiss is a coarse, foliated high‑grade metamorphic rock with distinct banding. Covers formation, texture, orthogneiss/paragneiss types, metamorphic grade, field identification, us…

Gondwana: the southern supercontinent and its legacy Gondwana Gondwana (Gondwanaland) was the great southern supercontinent that formed from Pangaea and later fragmented into the continents of the southern hemisphere and nearby landmasses.

Grain size (particle size) in sediments and soils Grain size Grain size (particle size) describes the diameter of individual sediment or rock fragments. It is classified by standard ranges, measured by sieving or instrumentation, and affects…

Granite: coarse‑grained intrusive igneous rock of continental crust Granite Granite is a durable, coarse‑grained intrusive igneous rock rich in quartz and feldspar. Common in continents, it forms from slowly cooled magma and is widely used in construction,…

Gravel: composition, classifications, uses and formation Gravel Loose rock fragments between about 2 mm and 64 mm used as aggregate, drainage, surfacing and landscaping; covers types, origins, processing and environmental considerations.

Great Oxygenation Event (GOE): Earth's first major rise in atmospheric oxygen Great Oxygenation Event The Great Oxygenation Event was the prolonged rise of free oxygen in Earth's atmosphere driven by photosynthetic microbes, reshaping geology, climate, and biology during the early…

Green River Formation — Eocene lake deposits and exceptional fossil beds Green River Formation An Eocene sequence of finely laminated lake sediments in the Uinta region, renowned as a lagerstätte for exceptionally preserved plants, fish and insects and for its varved record…

Greenhouse effect: how atmospheric gases warm the planet and why it matters Greenhouse effect The greenhouse effect is the process by which certain atmospheric gases trap outgoing infrared radiation, keeping Earth habitable. Human emissions have strengthened it, driving cli…

Greenhouse gas A greenhouse gas traps outgoing infrared radiation, warming a planet. Natural gases sustain Earth's climate; human emissions are increasing concentrations and driving modern warmin…

Greenstone belt (ancient metamorphosed volcanic rock formations) Greenstone belt Zones of very old, metamorphosed mafic volcanic and minor sedimentary rocks within Archean and Proterozoic cratons; important for early Earth studies and many metal deposits.

Greywacke: a dark, poorly sorted sandstone and its origins Greywacke Greywacke is a hard, dark, poorly sorted sandstone composed of mixed mineral and rock fragments in a fine clay matrix. Formed largely by submarine sediment gravity flows, it is com…

Grímsvötn Grímsvötn is Iceland's most active volcano, a subglacial basaltic system beneath the Vatnajökull ice cap in southeast Iceland, linked to the Laki fissure and notable for frequent e…

Gritstone: coarse siliceous sandstone, uses and geology Gritstone Gritstone is a hard, coarse-grained siliceous sandstone used historically for millstones and building; notable in northern England as Millstone Grit and important for geology, indu…

Ground (Earth surface and electrical reference) Ground Ground: the Earth's surface of soil, rock and sediment, and separately the electrical reference or earthing used for safety, fault protection and voltage measurement.

Groundwater: Subsurface Water, Aquifers, Uses, and Management Groundwater Comprehensive overview of groundwater: what it is, how it forms and moves, its roles for ecosystems and people, quality concerns, and principles for sustainable use and protection.

Global Boundary Stratotype Section and Point (GSSP) GSSP A GSSP (Global Boundary Stratotype Section and Point) is a physical reference point that formally defines the base of stages in the geologic time scale, established through interna…

Guyot (tablemount): flat‑topped underwater seamount Guyot A guyot, or tablemount, is a flat‑topped seamount formed by volcanic activity, surface erosion and subsequent subsidence. They are important for geology, paleoceanography and marin…

Hadean eon — Earth's earliest geologic eon (about 4.6 to 4.0 billion years ago) Hadean The Hadean is Earth’s earliest eon (≈4.6–4.0 Ga), marked by planetary accretion, core formation, heavy bombardment, early crustal evolution and an atmosphere low in free oxygen.

Hailstone A hailstone is a solid ball or lump of ice produced in strong thunderstorms. This article explains how hail forms, its structure, typical sizes, hazards, and how scientists measure…