Earth science

Low pressure area (meteorology) Low pressure area An explanation of low pressure areas: what they are, how they form, their structure and weather effects, common cyclone types, and important distinctions for forecasting and climat…

Lower Cretaceous Early epoch of the Cretaceous Period (about 145–100.5 Ma). Notable for long duration, shifting sea levels, characteristic rock groups (Wealden, Greensand, Gault) and important foss…

Lower Jurassic (Early Jurassic epoch) Lower Jurassic The Lower Jurassic (Early Jurassic) epoch lasted from about 201.3 to 174.1 million years ago. It records post‑extinction recovery, widespread marine deposits, diversifying dinosaur…

Lower Triassic Epoch Lower Triassic The Lower Triassic: the earliest epoch of the Triassic Period, beginning after the Permian–Triassic extinction and marked by continental red beds, arid environments, and a slow bio…

Mackenzie Large Igneous Province (MLIP) Mackenzie Large Igneous Province A Mesoproterozoic continental flood basalt province in Canada, formed about 1.27 billion years ago; dominated by the Mackenzie dike swarm, Coppermine flood basalts and related intr…

Magma: molten rock beneath Earth's surface Magma Magma is molten rock beneath the Earth's crust. This article explains its composition, types (felsic, mafic, intermediate), formation at tectonic settings, emplacement as intrusion…

Magnetic pole Points on a planetary magnetic field where the field is vertical; distinct from geographic poles and subject to movement, secular variation, and long-term reversals with practical…

Maipo (volcano) — Andean stratovolcano on the Argentina–Chile border Maipo (volcano) Maipo is an Andean stratovolcano on the Argentina–Chile border, notable for its steep cone, glaciers and Laguna del Diamante, and for its role in regional water supply, mountaineer…

Manicouagan impact structure (Manicouagan Reservoir) Manicouagan crater Large, multi-ring impact structure in Québec, Canada: a 100 km crater with a 70 km annular lake and central island, formed by an asteroid in the Late Triassic and studied for geolo…

Mantle — Earth layer, ceremonial cloak, and mollusc organ Mantle Mantle refers to several distinct concepts: the Earth's thick layer between crust and core, a cloak or ecclesiastical vestment, and the soft body tissue in molluscs that secretes s…

Marl: calcareous clay-rich sediment and its rock form marlstone Marl Marl is a soft, earthy sediment rich in carbonate minerals, clays and silt that forms in freshwater and marine settings. Hardened marl is marlstone; it has agricultural, geological…

Massif: Geologic mountain block formed by crustal uplift Massif A massif is a coherent block of the Earth's crust uplifted by tectonic forces and bounded by faults; this article explains its formation, features, examples, and how it differs fro…

Mauna Kea — White Mountain of Hawaii Mauna Kea Mauna Kea is a dormant shield volcano on the island of Hawaii, the state's highest peak and an important site for astronomy, ecology, and Native Hawaiian culture.

Mauna Loa Mauna Loa is a massive shield volcano on the Island of Hawaiʻi, known for its broad profile, frequent basaltic eruptions, summit caldera, rift zones, and active monitoring by the U…

Mediterranean climate: characteristics, distribution, and significance Mediterranean climate A temperate climate with dry summers and wet winters found around the Mediterranean and in five other world regions; overview, classification, causes, vegetation, uses, and notable…

Megathrust earthquake A megathrust earthquake is an extremely large interplate quake that occurs where one tectonic plate is forced beneath another at a subduction zone, often producing devastating shak…

Meiji Seamount — a flat-topped volcano in the Hawaiian–Emperor chain Meiji Seamount Meiji Seamount is an extinct, flat-topped underwater volcano (guyot) in the Hawaiian–Emperor seamount chain. It records ancient hotspot activity and is named for Japan’s Emperor Me…

Mercalli (Modified Mercalli) intensity scale Mercalli intensity scale A descriptive scale that rates earthquake shaking by observed effects on people, buildings and the landscape. It ranges from I (instrumental, not felt) to XII (catastrophic), disti…

Mesocyclone — rotating updraft in convective storms Mesocyclone A mesocyclone is a mid-scale rotating updraft (about 2–10 km wide) embedded in a convective storm. It is important in severe-weather processes and often precedes tornado formation.

Mesoproterozoic (1.6–1.0 billion years ago) Mesoproterozoic Middle era of the Proterozoic Eon (1.6–1.0 Ga). Key features include supercontinent cycles (Columbia breakup, Rodinia assembly), the rise of eukaryotes and early multicellularity.

Mesosphere: Earth's middle atmospheric layer Mesosphere The mesosphere is the atmospheric layer between roughly 50 and 90 km altitude. It is cold, thin, hosts meteors and noctilucent clouds, and is difficult to study because it lies abo…

Mesozoic Era: Age of Dinosaurs and the Rise of Modern Vertebrates Mesozoic The Mesozoic Era (about 252–66 million years ago), the middle era of the Phanerozoic, saw the rise of dinosaurs, early mammals, birds and flowering plants and ended with a major ma…

Mesozoic Marine Revolution: escalation of seafloor predation and faunal change Mesozoic marine revolution A major Mesozoic increase in marine predation that transformed benthic communities, promoting new predators, defensive shells, burrowing lifestyles and the shift from brachiopod to…

Messel Pit: Eocene lagerstätte and fossil treasure of Hesse, Germany Messel pit Former oil‑shale quarry near Messel, Hesse, Germany, the Messel Pit is a Middle Eocene (≈47 Ma) lagerstätte renowned for exceptionally preserved fossils, including early mammals; a…

Metamorphic rock: formation, types, and uses Metamorphic rock Metamorphic rock is bedrock changed in the solid state by heat, pressure, and fluids. This article explains origins, textures, common examples, economic uses, and how metamorphism…

Metamorphism (Geology): Processes, Types and Importance Metamorphism Metamorphism is the solid‑state alteration of rocks driven by heat, pressure, fluids, and deformation. This article explains causes, textures, types, metamorphic grade and why it m…

Meteorology: The Science of Weather and the Atmosphere Meteorology An overview of meteorology: its focus on atmospheric processes, observation methods, forecasting techniques, practical uses, history, and distinctions from related fields.

Methane hydrate (methane clathrate) Methane hydrate A crystalline ice-like solid in which methane molecules are trapped within water cages, occurring in marine sediments and permafrost; significant for energy potential and climate i…

Micropaleontology: the study of microfossils and their applications Micropaleontology Micropaleontology examines fossils too small to see unaided (typically

Mid‑Continent oil province Mid-Continent oil province A large onshore petroleum province in central and southern United States, spanning hundreds of fields and diverse basins across Arkansas, Kansas, Louisiana, New Mexico, Oklahoma an…

Middle Jurassic: Earth, life, and tectonics during the middle of the Jurassic Period Middle Jurassic Middle Jurassic epoch (c. 174.1–163.5 Ma): a geologic interval of shifting continents, evolving ecosystems, notable dinosaur faunas and important tectonic events that shaped later…

Middle Triassic Middle Triassic (about 247.2–237 Ma): the second epoch of the Triassic, marked by ecological recovery after the end‑Permian extinction, diversification of marine reptiles and archo…

Milankovich cycle Regular, long-term variations in Earth’s orbit and axis that change solar radiation patterns and influence long-term climate rhythms such as ice ages.

Mineral: naturally occurring inorganic solids and their study Mineral A mineral is a naturally formed, inorganic solid with a definite crystalline structure. This article explains their defining properties, classification, formation processes, common…

Mineral exploration: methods, stages, and economic importance Mineral exploration Overview of mineral exploration: objectives, common techniques, program stages, data handling and classification, economic evaluation, industry structure, and environmental and soc…

Mineral water Water from underground sources that acquires dissolved minerals from rocks; valued for taste, bottling, spa use and traditional health claims. Composition, carbonation and regulati…

Mineralogy: study of minerals, their properties, and uses Mineralogy Mineralogy is the scientific study of minerals: their chemistry, crystal structure, physical properties, identification methods, history, and practical uses in industry and everyda…

Mining: extraction of minerals, fuels and industrial materials Mining Mining is the extraction of non‑renewable materials from the Earth. This article explains types of mining, common resources, history, environmental and safety issues, economic role…

Miocene Epoch — climate transition, life, and geologic changes (23–5.33 Ma) Miocene The Miocene (about 23–5.33 million years ago) was a pivotal epoch of the Cenozoic marked by global cooling, expansion of grasslands, diversification of mammals and marine life, and…

Mississippian (geology) The Mississippian is the early part of the Carboniferous (about 359–323 million years ago), known for widespread shallow seas, extensive limestone deposition and rich marine fossil…

Mohs scale of mineral hardness A descriptive overview of the Mohs scale: its origin, the ten reference minerals, how the scratch test works, practical uses, and limitations for modern hardness measurement.

Moment magnitude scale A modern earthquake magnitude scale based on seismic moment; logarithmic and better suited for large events than older local scales.

Morrison Formation A widespread Upper Jurassic sedimentary rock unit in the western United States, famed for abundant dinosaur fossils and varied floodplain, river, and lake deposits.

Mount Agung — Bali's highest mountain and active volcano Mount Agung Mount Agung is a stratovolcano on Bali, Indonesia. It is the island's highest point, a sacred site for Balinese Hinduism, and has produced destructive eruptions in 1963–64 and 2017…

Mount Alayta Mount Alayta is a shield volcano in Ethiopia's Afar region, rising about 1,496 m. Noted for extensive early 20th-century lava flows, its last recorded activity occurred around 1915…

Mount Baker (Koma Kulshan): Stratovolcano in Washington State Mount Baker Mount Baker, also called Koma Kulshan, is an active stratovolcano in the North Cascades of Washington, noted for heavy glaciation, recreational use, and volcanic hazards monitored…

Mount Batur Mount Batur is an active volcano on Bali rising inside a large caldera; notable for its dramatic crater, Lake Batur, long eruptive history and popular sunrise treks near villages w…

Mount Bulusan: active stratovolcano in Sorsogon, Philippines Mount Bulusan Mount Bulusan is an active stratovolcano in southeastern Luzon, Philippines, known for frequent steam-driven eruptions, nearby protected forest, and ongoing monitoring because of h…