Earth science

Rapid deepening of tropical cyclones Rapid deepening Rapid deepening describes a fast fall in a tropical cyclone's central pressure, usually linked to swift intensification. It highlights causes, measurement, impacts, forecasting cha…

Red beds: oxidized continental sedimentary rocks and their significance Red beds Red beds are terrestrial sedimentary strata colored by iron oxides. This entry reviews their composition, formation, geological distribution, fossil and economic importance, and di…

Relative dating: principles and uses in geology, paleontology and archaeology Relative dating Method for ordering past events by comparison of layers, fossils, and artifacts. Describes principles, common techniques, historical development, applications, and limits compared…

Relative humidity Relative humidity describes how much water vapor air contains compared with the maximum it could hold at that temperature; it affects weather, comfort, and many technical processes…

Rhyacian: Palaeoproterozoic period (2.30–2.05 billion years ago) Rhyacian Second period of the Palaeoproterozoic, marked by early Paleoproterozoic glaciation, increasing oxygenation, tectonic reconfiguration and some of the oldest evidence for complex eu…

Rhynie chert Lower Devonian hot-spring chert near Rhynie, Aberdeenshire, Scotland, exceptionally preserving early land plants, fungi, lichens, algae and arthropods in three-dimensional cellular…

Rhyolite (high-silica volcanic rock) Rhyolite Rhyolite is a light‑colored, fine‑grained volcanic rock with very high silica content. It is the extrusive equivalent of granite and commonly forms in explosive eruptions and lava…

Rhythmite (rhythmic sedimentary layering) Rhythmite Rhythmite: repeated layers of sediment or sedimentary rock produced by regular environmental cycles (annual varves, tides, seasonal floods), used to read past environments and clim…

Richter scale A logarithmic scale originally devised to express an earthquake's local magnitude. Describes amplitude and energy relationships, historical origin, limitations, and modern usage in…

Ridge (meteorology) A ridge is an elongated region of relatively high atmospheric pressure that produces subsidence, stable weather, and warm conditions. Ridges contrast with troughs and play a key ro…

Riebeckite (including crocidolite, or blue asbestos) Riebeckite Riebeckite is an amphibole silicate mineral that occurs as compact crystals and as fibrous crocidolite (blue asbestos). It is notable for its color, industrial uses in the past, an…

Rift (Geology): Formation, Types, and Significance Rift (geology) A geological rift is where the Earth's crust and lithosphere are pulled apart, creating valleys, volcanism, earthquakes and sometimes new ocean basins. Causes, stages, features and…

Robert Arbuckle Berner (1935–2015), American geochemist and carbon cycle modeler Robert Berner Geochemist and Yale professor known for quantitative models of the long‑term carbon cycle, contributions to sedimentary geochemistry, and decades of teaching in geology and geophys…

Rock (geology) — types, formation, and significance Rock (geology) An overview of rocks: naturally occurring solid aggregates of minerals, their major types (igneous, sedimentary, metamorphic), formation processes, textures, study, and practical i…

Rock cycle: how Earth's rocks form, change, and interact Rock cycle Overview of the rock cycle: the processes that transform igneous, sedimentary and metamorphic rocks; main mechanisms, environments, timescales, and why the cycle matters for landsc…

Rock flour (glacial flour): formation, properties, and uses Rock flour Rock flour is the fine, clay-sized powder produced by glacial grinding or milling of rock. It affects water color and ecology, has industrial and agricultural uses, and differs fro…

Rodinia: a Neoproterozoic supercontinent and its legacy Rodinia Rodinia was a Neoproterozoic supercontinent assembled around 1.1 billion years ago and fragmented by the Tonian–Cryogenian, with major effects on climate and early life. Its config…

Rose rock (barite rose) — Oklahoma state rock Rose rock Rose rock is a rosette-shaped barite (barium sulfate) mineral specimen known for petal-like crystals. It is the official state rock of Oklahoma, designated in 1968, and is collecte…

Royal Tyrrell Museum of Palaeontology — Alberta's premier fossil museum Royal Tyrrell Museum of Palaeontology A leading palaeontology museum and research centre in Alberta's Badlands, housing an extensive fossil collection, active research programs, public exhibits and educational outreach…

Sahara Pump Theory A geoclimatic model explaining recurrent humid phases in the Sahara that opened migration corridors for plants, animals and humans between Africa, the Middle East, Europe and Asia.

Saharan Air Layer (SAL) Saharan Air Layer A warm, dry, dust-laden mass of air that forms over the Sahara and drifts west across the Atlantic, influencing weather, tropical cyclone development, air quality and ocean ecosyst…

Sakurajima — active volcano in Kagoshima, Japan Sakurajima Sakurajima is an active volcanic complex in Kagoshima Prefecture, Japan, noted for frequent eruptions, the 1914 eruption that joined it to the mainland, heavy ashfall and its cultu…

Salinity (concentration of dissolved salts in water) Salinity Salinity measures the concentration of dissolved salts in water. This article explains units and methods, typical ranges, causes and history, ecological and practical importance, a…

Salt mine: geology, methods, history and uses Salt mine An accessible overview of salt mines: geology (halite), extraction methods, historical role, modern uses, reuse of workings and safety considerations for rock-salt deposits and ope…

Salt water (saline water) Salt water Salt water, or saline water, is water that contains significant dissolved salts. This article explains composition, salinity, physical properties, ecological roles, human uses and…

San Andreas Fault Major transform fault in California marking the Pacific–North American plate boundary; site of large historic earthquakes and an active area of study and hazard.

Sand: composition, formation, uses, and environmental concerns Sand Sand is a natural granular material of rock and mineral particles. This article explains its composition, grain sizes, environments, formation processes, common uses, and environme…

Sandstone: composition, formation, properties, and uses Sandstone Sandstone is a clastic sedimentary rock made of sand-sized grains and cement. This article explains its composition, varieties, formation, common uses, and how it differs from rela…

Schist — Foliated Metamorphic Rock Rich in Platy Minerals Schist Schist is a medium- to high-grade foliated metamorphic rock dominated by platy and elongated minerals. It forms from mudstones or volcanic protoliths and is named for its ease of s…

Sea breeze — coastal onshore winds and their effects Sea breeze A sea breeze is a daytime onshore wind driven by temperature contrasts between land and sea; it influences coastal weather, cooling, air quality, and local wind patterns.

Sea Caves: Formation, Features, and Significance Sea caves Sea caves are coastal chambers carved by waves into rock. This article explains how they form, their structure, ecological and human importance, and how they relate to arches, stac…

Sea glass and beach glass: origin, characteristics, and uses Sea glass Fragments of glass naturally smoothed and frosted by waves and abrasion. Overview of formation, colors and rarity, differences between saltwater 'sea glass' and freshwater 'beach g…

Sea ice: formation, structure, and importance Sea ice Sea ice is frozen ocean water that grows and melts in place. This article explains how it forms, its types and roles in climate and ecosystems, and how it differs from glaciers, ic…

Sea level: definition, measurement, and significance Sea level Sea level is the average surface height of the ocean used as the reference for elevation. This article explains mean sea level, how it is measured, what causes it to change, and wh…

Sea surface temperature (SST) Sea surface temperature Sea surface temperature (SST) is the temperature of the uppermost layer of the ocean. Measured by satellites, buoys and ships, SST is a key variable for weather, climate, ecosystem…

Seabed (sea floor): structure, ecology, exploration, and human impact Seabed The seabed is the ocean’s bottom surface. This article outlines its major geological zones, sediments, life forms, mapping and exploration methods, and the modern human pressures a…

Seafloor spreading: formation, evidence, and role in plate tectonics Seafloor spreading Seafloor spreading is the process by which new oceanic crust forms at mid-ocean ridges and moves outward, driving plate motions and recycling crust at trenches. Explains mechanism,…

Seamounts: Submerged Volcanoes, Ecosystems, and Hazards Seamount Seamounts are underwater mountains formed mainly by volcanic activity. This entry covers their formation, structure, ecology, mapping, human impacts, hazards and conservation chall…

Sediment: deposition, composition and geological significance Sediment Sediment is loose material deposited by water, wind, ice or gravity. This article describes composition, transport, depositional environments, diagenesis, sedimentary structures an…

Sedimentary rock Sedimentary rock: rocks formed by accumulation and lithification of sediment; types, formation processes, common examples, environments, uses, and how they differ from igneous and…

Sedimentology: study of sediments, processes, environments, and applications Sedimentology Sedimentology examines sediments and sedimentary rocks: how particles are produced, moved, deposited and transformed. It informs Earth history, resources, environmental change and…

Seismic wave Oscillations that travel through Earth after sudden energy release; includes body and surface waves, their properties, detection, and uses in seismology and exploration.

Seismogram: recorded traces of ground motion Seismogram A seismogram is a time-based record of ground movement captured by instruments. This article explains what seismograms show, how they are made, their history, uses, and key interpr…

Seismology: the study of Earth's vibrations and internal structure Seismology Seismology investigates vibrations of the Earth to reveal subsurface structure, earthquake processes, volcanic systems, and human-made events using seismometers and other sensors.

Seismometer A seismometer is an instrument that detects and records ground motion from earthquakes, explosions and other sources. Seismograms are used to locate events and to probe Earth’s int…

Severe weather: storms, causes, impacts, and preparedness Severe weather An overview of severe weather: types (thunderstorms, tornadoes, hurricanes, winter storms), how they form, common impacts, forecasting approaches, and guidance on preparedness and…

Shale: a fine‑grained sedimentary rock — characteristics, formation and uses Shale Shale is a fine‑grained sedimentary rock formed from compacted mud and clay. It is important as a record of past environments, a host for fossils and organic matter, and a source o…

Shale gas: formation, extraction, uses and impacts Shale gas Shale gas is natural gas trapped in fine-grained sedimentary rocks. This article explains its geology, how it is produced, uses, economic importance and environmental and social co…