Earth science

Andalusite (Al2SiO5): properties, formation, and uses Andalusite Andalusite is an aluminium nesosilicate mineral (Al2SiO5). An index mineral in metamorphic rocks, it occurs as orthorhombic crystals and as the cross-bearing variety chiastolite.

Annular hurricane A rare tropical cyclone type with a large, symmetric eyewall and a continuous ring of deep convection but few or no spiral rainbands, allowing unusually steady intensity.

Anoxic event: ocean oxygen depletion and its geological record Anoxic event An anoxic event is a prolonged loss of oxygen in parts of the ocean. This article explains causes, geological evidence, historical examples, modern dead zones and why these events…

Anticyclone (high-pressure system) Anticyclone A large-scale high-pressure weather system marked by descending air, outward surface flow and usually stable, clear conditions. Anticyclones influence regional climate, air quality…

Anticyclonic storm A rotating atmospheric system with anticyclonic (opposite) spin to cyclones; associated with high pressure, subsiding air, and distinctive regional weather effects and blocking pat…

Aquamarine (gemstone) Aquamarine Aquamarine is the blue‑green variety of beryl prized as a gemstone. Noted for its sea‑like hues, clarity and durability, it is the traditional birthstone for March and a popular je…

Aquifer: underground water-bearing formations and their importance Aquifer An aquifer is a subsurface layer of rock or sediment that holds and transmits groundwater. This article explains types, properties, uses, recharge, threats, and the scientific stud…

Archaean Eon: Earth's early geologic era of first rocks and life Archaean The Archaean eon (about 4.0–2.5 billion years ago) when the earliest known rocks, volcanic and metamorphic terrains, and microbial life emerged under a low-oxygen atmosphere.

Arkose: A Feldspar-rich Sandstone — Composition, Formation, and Significance Arkose Arkose is a coarse, feldspar-rich sandstone formed chiefly from the breakdown of granite; this article explains its composition, formation environments, diagenesis, uses and how it…

Asbestos: properties, history, uses, health effects and management Asbestos Asbestos is a group of naturally occurring fibrous silicate minerals once widely used for heat resistance and insulation. This article covers types, uses, health risks, history, an…

Ash: residue from fire, volcanic material, and the ash tree Ash Overview of ash in its main meanings: combustion residue (wood and coal ash), volcanic ash, and trees of the genus Fraxinus, including uses, hazards, history, and distinctions such…

Asthenosphere: the weak, flowing layer beneath Earth's lithosphere Asthenosphere A mechanically weak, partially ductile zone in the upper mantle (roughly 100–350 km deep) that deforms and flows on geological timescales, enabling plate tectonics and influencing…

Atlantic Ocean: geography, history, ecology, and human uses Atlantic Ocean Overview of the Atlantic Ocean including size, physical features, origins, major currents, ecosystems, human uses and environmental challenges.

Atmosphere of Earth: composition, structure, functions, and origins Atmosphere of Earth A concise overview of Earth's atmosphere: its composition, layered structure, protective roles, origin and evolution, and notable boundaries and particulates.

Atmosphere of Mars The thin, CO2-dominated envelope surrounding Mars: composition, pressure, weather, seasonal cycles, atmospheric loss, and key discoveries from spacecraft observations.

Atmospheric circulation: global wind systems and their drivers Atmospheric circulation Large-scale movement of air that redistributes heat, moisture, and momentum on Earth. Explains the driving forces, the three-cell structure, Coriolis effects, and climate impacts.

Atmospheric convection: processes, types, and role in weather and flying Atmospheric convection Overview of atmospheric convection: causes, types (surface-driven and spontaneous), physical mechanisms, scales, weather impacts, examples such as thermals for gliding, and distinc…

Augite — a common dark pyroxene mineral Augite Augite is a dark, typically green to black member of the pyroxene mineral group, common in mafic igneous and some metamorphic rocks and useful in petrology for interpreting rock fo…

Augustine Volcano A frequently active stratovolcano in Cook Inlet, Alaska, known for explosive eruptions, pyroclastic flows, and hazards to aviation, shipping and nearby communities; monitored for p…

Australian impact structure (MAPCIS) — proposed megacrater in central Australia Australian impact structure MAPCIS is a hypothesized giant meteorite impact centered in the Northern Territory between Uluru and Mount Conner; proposed diameters range from ~600 km to a broader 2,000 km ring…

Bajocian — Middle Jurassic age and stage Bajocian The Bajocian is a stage of the Middle Jurassic (about 170.3–168.3 Ma), defined by marine strata and ammonite biozones. It succeeds the Aalenian and precedes the Bathonian.

Banded iron formation (BIF): composition, origin, and significance Banded iron formation Banded iron formations are layered sedimentary rocks of the Precambrian made of alternating iron-rich and silica- or shale-rich bands. They record early ocean chemistry and are maj…

Baroclinic: stratification, instability, and atmospheric importance Baroclinic Baroclinic describes a fluid state where density depends on both temperature and pressure, producing misaligned isobars and isopycnals and enabling phenomena like mid-latitude cycl…

Basalt — common extrusive igneous rock and its properties Basalt Basalt is a dark, fine‑grained mafic volcanic rock formed from mantle-derived lava. This entry describes its composition, textures, tectonic settings, industrial uses, metamorphism…

Basement (geology): crystalline and metamorphic rocks beneath sedimentary cover Basement (geology) Basement in geology denotes the rocks—typically metamorphic or igneous—underlying sedimentary layers or basins. This article explains its definition, composition, significance, and…

Bathymetry: mapping and measuring underwater terrain Bathymetry Bathymetry is the measurement and mapping of underwater topography. It documents depths and seafloor shapes for navigation, science, engineering and environmental management.

Beach erosion: causes, coastal landforms and management Beach erosion Beach erosion is the removal or loss of sand and shoreline by waves, currents, tides, storms, sea-level change and human activity; it shapes coasts and requires diverse management…

Bed (geology): the smallest stratigraphic rock unit and its significance Bed (geology) A bed is the smallest lithostratigraphic unit in geology, a rock layer bounded by bedding planes. It records depositional changes and is important for mapping, resource study and e…

Bedrock: definition, composition, mapping and engineering significance Bedrock Bedrock is the solid rock beneath surface materials. This article explains its types, weathering profile, methods to locate it, and why it matters for geology and engineering.

Bentonite: properties, formation, and industrial uses Bentonite Bentonite is a swelling clay formed by alteration of volcanic ash. Rich in smectite minerals, it absorbs water, exchanges cations, and is widely used in drilling, sealing, foundry…

Biosphere — Earth's global system of living organisms and their environments Biosphere The biosphere is Earth's global system of living organisms and their environments, spanning deep subsurface microbes to high-atmosphere life. It includes natural ecosystems and hum…

Black smoker (deep-sea hydrothermal vent) Black smoker A black smoker is a type of deep-sea hydrothermal vent that emits mineral-rich, superheated fluids and builds chimney structures, supporting unique chemosynthetic ecosystems and co…

Blake River Megacaldera Complex An Archean volcanic megacaldera complex spanning the Ontario–Quebec border, notable for its large size (~3,000 km²), ~2.7 billion-year age, complex caldera architecture and mineral…

Blue Lias: Jurassic limestone–shale sequence of southern Britain Blue Lias Blue Lias is a layered limestone and shale formation of late Triassic–early Jurassic age in southwest England and south Wales, noted for its fossils, coastal exposures and use as b…

Bornhardt: dome-shaped inselbergs and their geology Bornhardt Bornhardt — a large, rounded, steep-sided rock dome, typically of granite or gneiss. Formed by long weathering and differential erosion, common as isolated inselbergs and studied f…

Boulder (large rock) — definition, formation, uses and distinctions Boulder A boulder is a very large clast of rock — in geology typically >256 mm — formed and moved by processes such as glaciation, weathering, or mass wasting; important in landscapes, eco…

Breccia: composition, formation, types, and uses Breccia Breccia is a coarse rock made of angular fragments cemented into a matrix. This article explains its composition, origins (sedimentary, tectonic, volcanic, impact), practical uses…

Burgess Shale: a Middle Cambrian fossil lagerstätte in the Canadian Rockies Burgess Shale Exceptionally preserved Middle Cambrian fossil deposit in British Columbia, notable for soft-tissue preservation and diverse, unusual early animal forms discovered at Fossil Ridge.

Calcium–Aluminum‑rich inclusions (CAIs) Ca-Al-rich inclusions Calcium–Aluminum‑rich inclusions are refractory mineral assemblages found in primitive meteorites; they are among the oldest solids in the solar system and key to early‑solar‑syste…

Cainozoic (Cenozoic) — the current geological era Cainozoic The Cainozoic (Cenozoic) era began about 66 million years ago and continues today. It saw continents reach modern positions, mammal dominance, progressive cooling and the ice ages,…

Calcite: common calcium carbonate mineral and its properties Calcite Calcite is a widespread carbonate mineral (CaCO3) found in sedimentary, metamorphic and hydrothermal settings. This article outlines its properties, formation, varieties, uses and…

Caldera (volcanic collapse formation) Caldera A caldera is a large volcanic depression formed when a magma chamber empties and the ground above collapses; this article explains formation, types, famous examples, impacts and mo…

Caledonian orogeny A major Paleozoic mountain-building episode (Ordovician–Early Devonian) produced by closure of the Iapetus Ocean, shaping northern Europe, Greenland and parts of eastern North Amer…

California Current: Cold Eastern Boundary Current of the Northeast Pacific California Current A broad, cold ocean current that flows southward along the western coast of North America, driving coastal upwelling, rich marine ecosystems, and regional climate patterns.

Calymmian Period (Mesoproterozoic, 1.6–1.4 Ga) Calymmian The Calymmian (1.6–1.4 billion years ago) is the earliest period of the Mesoproterozoic, characterized by continental rifting, the breakup of the Columbia supercontinent and contin…

Cambrian period — early Palaeozoic interval of rapid animal diversification Cambrian The Cambrian (≈541–485 Ma) is the first period of the Palaeozoic and Phanerozoic, marked by the Cambrian explosion, widespread marine life, the appearance of many animal phyla, and…

Canadian Hurricane Centre — role, operations and notable storms Canadian Hurricane Centre The Canadian Hurricane Centre (CHC) monitors tropical cyclones near Canada, issues watches and warnings, coordinates with international partners, and provides public guidance from…

Canadian Shield (Laurentian Plateau) Canadian Shield Vast Precambrian region of exposed igneous and metamorphic rock forming the ancient core of North America, surrounding Hudson Bay and supplying minerals, forests, lakes and hydroel…