Earth science

Ediacaran Period: the late Neoproterozoic era of early large-bodied life Ediacaran Geological period (≈635–541 Ma) named for the Ediacara Hills, notable for the earliest large-bodied multicellular fossils and distinctive soft-bodied assemblages that predate the C…

El Niño–Southern Oscillation (ENSO): causes, phases, impacts and measurement El Niño–Southern Oscillation ENSO is a recurring ocean–atmosphere phenomenon in the tropical Pacific with warm (El Niño) and cool (La Niña) phases that alter global weather patterns, ecosystems and climate var…

Ellesmere Island Volcanics — Cretaceous volcanic province of the High Arctic Ellesmere Island Volcanics A group of extinct Cretaceous volcanoes and lava flows on Ellesmere Island, Nunavut. The northernmost known volcanic rocks on Earth and part of the Arctic Cordillera, important to…

Emeishan Traps: Permian flood basalts of southwestern China Emeishan Traps A geological overview of the Emeishan Traps, a Permian large igneous province in Sichuan, China, its geology, age, environmental impact, and role in debates over mass extinctions.

Emerald (gemstone) Emerald Emerald is the green variety of beryl prized as a gemstone. This article explains its composition, color and clarity, history and major sources, treatments, uses, and how its value…

End‑Triassic extinction event End-Triassic extinction event A major late Mesozoic biotic crisis at the Triassic–Jurassic boundary (~201 Ma) that removed many marine and terrestrial groups and helped open ecological space for Early Jurassic…

End–Ordovician extinction event A major Late Ordovician global biotic crisis marked by two pulses of marine extinctions driven by glaciation, sea‑level change, ocean anoxia and shifts in the carbon cycle.

Enhanced Fujita scale A damage-based system for rating tornado strength, the Enhanced Fujita (EF) scale refines the original Fujita scale using damage indicators to estimate wind speeds and assess torna…

Environmental geology: principles, scope, and practical applications Environmental geology Environmental geology applies geological science to environmental problems, resource management, hazard assessment, waste disposal, and land-use planning to reduce pollution and ma…

Eoarchaean (Eoarchean): the earliest interval of the Archaean Eoarchaean The Eoarchaean (4.0–3.6 billion years ago) is the first era of the Archaean eon, marking the stabilization of Earth's crust, early crustal growth, and the window when life likely o…

Eocene Epoch: warm climates, early modern mammals, and the path to the Oligocene Eocene Geological epoch from about 56 to 33.9 million years ago. Known for very warm climates, the Paleocene–Eocene Thermal Maximum, rapid mammal diversification, and the shift to cooler…

Eocene–Oligocene extinction event: climatic transition and biotic turnover Eocene–Oligocene extinction event Global biotic turnover at the Eocene–Oligocene boundary (~33.9 Ma) marked by rapid cooling, Antarctic glaciation, major marine extinctions and ecosystem shifts; causes remain activ…

Eon (Geologic Time Interval) Eon An eon is the largest formally recognized division of geologic time, spanning hundreds of millions to billions of years and composed of eras, periods and epochs.

Epicenter: point on Earth's surface above an earthquake focus Epicenter The epicenter is the surface location directly above an earthquake's focus (hypocenter). This article explains definition, how seismologists locate it, practical importance, and ke…

Epoch (geology): definition, hierarchy, history and examples Epoch (geology) An epoch is a subdivision of a geological period. This article explains what epochs are, how they are named and defined, examples from the Cenozoic, and how international bodies st…

Era (geology) Era A geologic era is a major division of Earth’s history lasting tens to hundreds of millions of years, defined by characteristic rock layers, fossil changes and major events. Eras gr…

Erosion: Causes, Processes, Effects and Control Erosion Erosion is the natural removal and transport of soil and rock by agents such as water, wind, ice and gravity. This article explains mechanisms, impacts, geological role and mitigat…

Erta Ale — active shield volcano in Ethiopia Erta Ale Erta Ale is a low shield volcano in Ethiopia's Afar Region, known for its long-lived lava lake, frequent effusive activity, and its location in the tectonically active Danakil Depr…

Eruption: geological events, medical meanings, and general definition Eruption Eruption denotes a sudden breaking out or release, most often referring to volcanic activity but also to tooth emergence, skin eruptions, and other sudden releases. Overview, types…

Eryops: a Permian temnospondyl amphibian Eryops Eryops was a large, semi‑aquatic temnospondyl amphibian from the Permian of North America, known for its heavy skull, sturdy limbs and numerous fossils found in red beds and other…

Eucrite — basaltic achondrite from asteroid 4 Vesta Eucrite Eucrites are basaltic achondritic meteorites from asteroid 4 Vesta (HED group). This article summarizes their composition, origin, classification, scientific importance and disting…

Eurasian Plate One of Earth's major tectonic plates, covering most of Europe and northern Asia and extending into adjacent ocean basins; shapes mountain ranges, seismic zones, and continental con…

Exogeny: External Causes and Influences in Earth Science and Other Fields Exogeny Exogeny denotes processes or influences that originate outside a system. This article explains the concept across geology, astronomy, biology and social sciences, with examples and…

Extratropical cyclone: mid-latitude low-pressure systems and their impacts Extratropical cyclone A comprehensive overview of extratropical (mid-latitude) cyclones: structure, formation, life cycle, hazards, and how they differ from tropical systems.

Extrusion: Geological Eruptions and Industrial Shaping Processes Extrusion Extrusion refers to material forced outward: in geology, magma expelled as lava or pyroclasts; in industry, material shaped by pushing through a die to form continuous profiles and…

Eye of a Tropical Cyclone Eye (cyclone) The eye is the relatively calm, low-pressure center of a tropical cyclone. This article explains its structure, formation, variations, hazards and role in storm intensity and forec…

Facies (geology): rock appearance, environments, and stratigraphic significance Facies Facies are bodies of rock whose appearance and composition reflect particular depositional environments and processes. This article explains types of facies, how they form, how the…

Geologic fault — fractures and movement in the Earth's crust Fault (geology) A geologic fault is a fracture in the Earth's crust where blocks of rock have moved. Faults shape landscapes, produce earthquakes, and reveal past tectonic forces and stress regime…

Feldspar: major rock-forming tectosilicate minerals Feldspar Feldspars are the most abundant group of rock-forming tectosilicate minerals in Earth’s crust, important in petrology, industry and dating methods; they form in igneous, metamorphi…

Felsic: light, silica-rich igneous minerals and rocks Felsic Felsic describes silica-rich, light-coloured igneous minerals and rocks (like granite and quartz). Covers composition, common minerals, formation, tectonic settings, uses and disti…

Fezouata Formation An Early Ordovician Moroccan Lagerstätte with exceptionally preserved fossils that extend Burgess Shale–type assemblages beyond the Cambrian and illuminate early Paleozoic marine e…

Fissure vent (volcanic fissure) Fissure vent A fissure vent is a linear volcanic opening that emits lava and gases, producing extensive flows often associated with rift zones, flood basalts and lava tubes.

Flash Flood: Causes, Characteristics, Impacts and Safety Flash flood Flash floods are sudden, fast-rising floods that inundate low-lying areas after intense rainfall, dam failures, rapid snowmelt or other abrupt water releases; they pose high risk d…

Flat Earth: history, beliefs, and cultural influence Flat Earth A neutral overview of flat Earth ideas: ancient models, development of spherical understanding, modern flat-Earth movements, scientific tests, cultural myths, and notable historica…

Flat Earth Society Organization advocating a flat-Earth model; founded in 1956, rooted in earlier zetetic movements, now largely a small movement sustained online and notable for conspiracy claims an…

Flint: Formation, properties, and historical uses Flint Flint is a hard, silica-rich sedimentary rock (a form of chert) that forms as nodules in chalk and other limestones. It has distinctive fracture, archaeological importance, and var…

Flood basalt (trap) provinces: formation, characteristics, and global significance Flood basalt Flood basalts are vast, low-viscosity basaltic lava flows produced by enormous volcanic events that form plateaus and oceanic plateaus, with major geological and environmental impa…

Fog: formation, types, effects, and notable facts Fog An accessible overview of fog: what it is, how it forms, common types, impacts on visibility and transportation, historical notes, and distinctions from mist and low clouds.

Fold (geology): Types, Formation, and Significance Fold (geology) A fold is a bend in originally planar rock layers produced by ductile deformation under stress. This article describes fold geometry, causes, scales, classification and their impor…

Fossil: remains, traces, and the science of ancient life Fossil A fossil is the preserved remains or trace of an organism from the geological past. This article explains how fossils form, types, preservation, significance, and how scientists st…

Fossil fuels: formation, types, uses, history and impacts Fossil fuel Fossil fuels are energy-rich materials formed from ancient organic matter. This article describes their composition, how they form and are extracted, historical development, common…

Fossil water (palaeowater): ancient groundwater and subglacial reserves Fossil water Fossil water (palaeowater) is ancient water stored for millennia in aquifers or beneath ice. This entry explains definitions, occurrences, dating methods, examples, uses, and manag…

Fracture (geology) A fracture is any break or discontinuity in rock. This article describes types (joints, faults), formation processes, controls on fluid flow, measurement methods, and importance in…

Franciscan Assemblage (Franciscan Complex) of coastal California Franciscan Assemblage A geological assemblage of mixed oceanic and continental rocks exposed near the San Francisco Peninsula, notable for its mélange, blueschist metamorphism, serpentinite, and role in…

Freezing rain: formation, hazards, and differences from sleet Freezing rain Freezing rain occurs when liquid precipitation freezes on contact with surfaces below freezing, producing hazardous ice coatings. This article explains how it forms, its dangers, d…

Frost: formation, types, effects on plants and protection Frost Frost is ice deposited when water vapor freezes on cold surfaces. This article explains how frost forms, its main types, impacts on agriculture and practical ways to reduce damage.

Frost heaving: causes, effects, and mitigation of freeze-induced soil uplift Frost heaving Frost heaving is the upward movement of soil when water in the ground freezes and forms ice; it affects infrastructure, agriculture, and landscapes in cold climates and can be redu…

Fujita scale A damage-based scale for rating tornado intensity, developed by T. T. Fujita; replaced by the Enhanced Fujita scale in many countries but still important historically and conceptua…