Earth science

Peridot: the gem-quality form of olivine and its properties, history, and uses Peridot Peridot is the green gem variety of the mineral olivine. This article covers its composition, color origin, sources, cultural history, gemological properties, and care for jewelry…

Peridotite: an ultramafic igneous rock of the Earth's mantle Peridotite Peridotite is a coarse-grained, ultramafic igneous rock dominated by olivine and pyroxene; it is a major constituent of the upper mantle and important for mantle processes and mine…

Period (geology) A geologic period is a major unit of the geologic time scale, ranking below an era and above an epoch; it groups rock layers and fossils formed during a distinct interval of Earth…

Permafrost: frozen ground, processes, distribution, and consequences Permafrost Permafrost is ground that remains at or below 0 °C for at least two years. This article explains its definition, structure, global distribution, environmental roles, and effects of…

Permian Period: Last Chapter of the Paleozoic and the Great Extinction Permian The Permian (about 299–252 million years ago) was the final period of the Paleozoic Era, notable for diverse terrestrial life, major climatic shifts, assembly of Pangaea, and the l…

Permian–Triassic extinction event Earth's largest mass extinction ~252 million years ago that ended the Permian and reshaped life; major causes debated, with Siberian Traps volcanism central to most explanations.

Permineralization: how mineral-rich fluids preserve biological structure Permineralization Permineralization is a fossilization process in which minerals carried by water fill the pores of organic tissues, preserving internal anatomy from cells to bones with exceptional…

Petrified Wood: Fossilized Trees and the Process of Petrification Petrified wood Petrified wood is wood that has undergone mineral replacement and permineralization, preserving original structure in stone. This article covers formation, composition, uses, and n…

Petroleum (Crude Oil): Origin, Properties, Uses, and Impacts Petroleum Comprehensive overview of petroleum: composition, geological formation, extraction, refining, major uses, and environmental and economic implications.

Petroleum industry: scope, operations, history and contemporary issues Petroleum industry Overview of the petroleum industry covering exploration, production, refining, transport, products, history, uses and modern challenges including environmental and geopolitical asp…

Petrology: The Scientific Study of Rocks Petrology Petrology examines rocks' origin, composition, and history. It links mineralogy and geology, uses microscopy and chemistry, and informs resource assessment, tectonics, and planetar…

Phanerozoic Eon: the Age of Visible Life Phanerozoic The Phanerozoic is the current eon on Earth’s geologic timescale, beginning about 541 million years ago and marked by abundant, diverse animal life preserved in the fossil record.

Pitchblende (uraninite): a uranium-rich radioactive mineral Pitchblende Pitchblende, also called uraninite, is a dense black uranium ore. This article describes its composition, physical traits, history, uses (including uranium fuel and dating) and saf…

Planetary core: composition, structure, and role within planets Planetary core The planetary core is the central region of a planet, typically dense and metallic. This article explains core composition, layered structure, formation, effects on magnetic fields…

Planetary geology: the study of otherworldly rocks, surfaces, and processes Planetary geology Planetary geology (astrogeology) examines the composition, structure, and evolution of planets, moons, asteroids, comets and meteorites using remote sensing, samples, comparative m…

Plate boundary Zones where Earth's tectonic plates meet and interact; types include divergent, convergent (subduction and continental collision), transform, and conservative margins, with charact…

Plate tectonics: the structure, processes, and effects of Earth's moving plates Plate tectonics Plate tectonics is the unifying theory that describes the rigid lithosphere divided into plates whose interactions shape Earth’s surface, driving earthquakes, volcanism, mountain b…

Pleistocene: Ice Ages, megafauna, and the rise of modern humans Pleistocene The Pleistocene (2.6 million–11,700 years ago) was an epoch of repeated glaciations, large mammals, major environmental change, and key stages in human evolution and migration.

Plinian eruption A Plinian eruption is a highly explosive volcanic event that generates sustained high eruption columns, widespread pumice and ash fall, pyroclastic flows, and sometimes caldera col…

Pliocene Epoch: climate change, life, and early hominins Pliocene The Pliocene (about 5.3–2.6 million years ago) was a geologic epoch marked by global cooling, expansion of grasslands, faunal exchanges, and important developments in hominin evolu…

Plutonism — the theory that igneous rocks form from Earth's internal heat Plutonism Plutonism is the geological theory that igneous rocks form from Earth’s internal heat and molten material. Explains its 18th‑century origins, James Hutton’s role, and the debate wi…

Polar climate: definition, characteristics, distribution and impacts Polar climate Overview of polar climates: definitions under the Köppen system, main features (tundra vs ice cap), typical locations, ecology, human presence and contemporary changes.

Polar low — mesoscale cyclones of the polar oceans Polar low Compact, short-lived low-pressure cyclones over high-latitude seas. Produce gale winds, heavy snow and hazardous seas; important for shipping, offshore operations and high-latitude…

Polar night: prolonged winter darkness in Earth's polar regions Polar night Extended periods of darkness that occur within the Arctic and Antarctic circles due to Earth's axial tilt; duration and intensity vary with latitude and affect ecosystems, human he…

Polar vortex: large-scale cyclonic circulation near Earth's poles Polar vortex A polar vortex is a persistent, large cyclonic circulation in the high-latitude atmosphere. It shapes polar and mid-latitude weather, has seasonal variability, and interacts with j…

Popocatépetl: Mexico’s active stratovolcano Popocatépetl Popocatépetl is an active stratovolcano in central Mexico, rising to 5,426 m (17,802 ft). It is a major geological feature, cultural symbol and closely monitored volcanic hazard ne…

Port silt loam — Oklahoma's state soil Port Silt Loam Port silt loam is a silt-dominant soil series known as Oklahoma's state soil, formed on Permian red-bed rocks, notable for its reddish hue and importance for grassland and agricult…

Portland limestone (Portland stone) Portland limestone A pale, oolitic limestone deposited in the Late Jurassic around the Isle of Portland, England, widely used as a durable building and dimension stone and notable for its chert bands…

Precambrian: Earth's early supereon from formation to the rise of complex life Precambrian The Precambrian covers Earth's history from its formation (~4.56 billion years ago) to the start of the Cambrian (~542 million years ago), including the Hadean, Archean and Protero…

Precipitation: forms, formation, measurement, and impacts Precipitation Comprehensive overview of precipitation: how it forms, common types (rain, snow, sleet, hail, dew, frost), how it is measured, and its environmental and societal importance.

Pressure gradient (fluid dynamics and meteorology) Pressure gradient The pressure gradient quantifies how pressure changes in space within a fluid. It is a vector quantity that drives forces and flows (in meteorology it helps produce winds); SI unit…

Prospecting: search for minerals, fossils and precious metals Prospecting Prospecting is the physical search for minerals, fossils or precious metals. It ranges from hobbyist fossicking to professional mineral exploration and includes specific methods, t…

Proterozoic Eon: geology, climate, and the rise of complex life Proterozoic The Proterozoic (about 2.5–0.54 billion years ago) marks continental assembly, atmospheric oxygenation, major glaciations and the first abundant multicellular organisms before the…

Prudhoe Bay Oil Field Largest oil field in the United States and North America, located on Alaska's North Slope; discovered in the 1960s and central to the Trans-Alaska Pipeline and regional economy.

Puddingstone (conglomerate rock) Puddingstone Puddingstone is a hard, silica-cemented conglomerate made of rounded pebbles set in a dense matrix; noted for durability, regional varieties, and uses in tools and building.

Pumice Lightweight, porous volcanic glass formed during explosive eruptions. Known for a frothy, vesicular texture; used as an abrasive, lightweight aggregate, and soil amendment. Can flo…

Pyrite (Fool's Gold): Properties, Formation, Uses, and Hazards Pyrite Pyrite (FeS2), commonly called fool's gold, is an iron sulfide mineral known for its metallic luster, cubic crystals, geological occurrence, uses, and environmental effects.

Pyroclastic flow (pyroclastic density current) Pyroclastic flow A pyroclastic flow is a fast, ground-hugging current of hot gas and volcanic particles produced during explosive eruptions or dome collapse, capable of extreme heat, high speed, an…

Pyrolusite (natural manganese dioxide mineral) Pyrolusite Pyrolusite is the most common natural form of manganese dioxide (MnO2). An opaque, heavy oxide mineral, it has been used in glassmaking, pigments, chemical manufacture and as a bat…

Pyroxene (rock-forming inosilicate minerals) Pyroxene Pyroxenes are a major group of single-chain inosilicate minerals common in igneous and metamorphic rocks, important for petrology, classification, and interpreting Earth and planet…

Quartz: Properties, Varieties, Uses, and Geological Significance Quartz Quartz is a hard, abundant silica mineral (SiO2) with many crystalline and microcrystalline varieties; widely used in jewelry, electronics, glassmaking and as a major component of…

Quartzite: formation, properties, colors, and common uses Quartzite Quartzite is a hard, non-foliated metamorphic rock produced from sandstone; prized for durability, varied colours from mineral impurities, and use as dimension stone, aggregate, an…

Quaternary (geologic period) Quaternary The Quaternary is the most recent geologic period, beginning about 2.6 million years ago; it includes major ice ages, the rise of modern humans, and ongoing environmental change.

Quicksand: formation, properties, safety, and cultural perceptions Quicksand Quicksand is a water-saturated granular mixture that can behave like a liquid when stressed. This article explains how it forms, how it behaves, safety and escape techniques, and c…

QuikSCAT (Quick Scatterometer): ocean surface wind observations and legacy QuikSCAT QuikSCAT was a scatterometer satellite that provided routine ocean surface wind vector measurements for weather forecasting, storm monitoring and oceanography; it later aged and pr…

Rain and snow mixed (rain–snow mix) Rain and snow mixed Precipitation composed of both liquid rain and solid snowflakes. Covers formation, terminology differences, hazards, observation codes (RASN), and how it differs from sleet and fre…

Rain gauge: instruments for measuring liquid precipitation Rain gauge Overview of rain gauges: types, recording methods, siting and sources of error, measurement of liquid and solid precipitation, maintenance, historical notes and practical applicati…

Ranger Uranium Mine — site, history, and controversies Ranger Uranium Mine Ranger Uranium Mine in the Alligator Rivers region lies inside Kakadu National Park. A large uranium deposit, it has been mined, regulated, and contested for environmental and cult…