Earth sciences

Pentlandite

Pentlandite is a bronze-yellow iron-nickel sulfide mineral, (Fe,Ni)₉S₈, and the most important ore of nickel, mined at Sudbury and associated with pyrrhotite in ultramafic igneous rocks.

Perched water table

A perched water table is a local zone of saturation sitting above the regional water table, held there by a low-permeability layer and separated from the main groundwater by unsaturated soil.

Peridot

Peridot, also known as chrysolith, is the gem-quality yellowish-green variety of the mineral olivine, prized for its intrinsic iron-derived color and found in lavas and meteorites.

Peridotite

Peridotite is a coarse-grained ultramafic igneous rock rich in olivine, making up most of the Earth's upper mantle and reaching the surface in xenoliths and ophiolites.

Permafrost

Permafrost is ground, soil, or rock that stays at or below 0 °C for at least two years, underlying much of Alaska, Canada, Siberia, and Antarctica and storing large amounts of carbon.

Permafrost carbon feedback

The permafrost carbon feedback is warming amplified when thawing permafrost lets microbes decay ancient organic matter, releasing carbon dioxide and methane that warm the climate further.

The permanent wilting point (PWP) is the soil water content at which plants wilt irrecoverably, conventionally defined as water held at −1500 kPa, and with field capacity it bounds plant-available water.

Permeability (porous media)

Permeability, also called intrinsic permeability, is the capacity of a rock or porous material to transmit a fluid. It governs groundwater flow in aquifers and oil movement toward wells.

Permeameter

A permeameter is an apparatus that applies a known hydraulic gradient to water flowing through a soil sample, allowing its hydraulic conductivity to be determined.

Permian

The Permian is a geologic period from about 299 to 251 million years ago, the last of the Paleozoic Era, ending with the largest mass extinction on record.

Permian Basin (North America)

The Permian Basin is a large sedimentary basin underlying West Texas and southeastern New Mexico and one of the world's most prolific oil- and gas-producing regions.

Perovskite

Perovskite is a calcium titanate mineral, CaTiO₃, found in the Ural Mountains in 1839 and named after Count Lev Perovski; the name also covers the ABX₃ crystal-structure family.

Perpetua Resources

Perpetua Resources Corp., formerly Midas Gold until its 2021 renaming, is a mining company advancing the Stibnite Gold Project, a gold and antimony mine in central Idaho.

Perseverance Mine (Western Australia)

The Perseverance Mine is an underground nickel sulfide mine at Leinster in the Northern Goldfields of Western Australia, the largest orebody of BHP's Leinster Nickel Operation, suspended from October 2024.

Persistent scatterer InSAR

Persistent scatterer InSAR (PSInSAR, or PSI) is a radar technique that measures surface deformation with millimeter-scale velocity precision at phase-stable ground points in time series of interferometric SAR images.

Persistent scatterer interferometry

Persistent scatterer interferometry, developed at the Politecnico di Milano and first reported in 2000, is a radar technique measuring millimeter-scale ground deformation from stacks of satellite SAR images.

Perturbed parameter ensemble

A perturbed parameter ensemble, or perturbed physics ensemble, is a climate modeling method that runs one model many times with varied parameter values to sample uncertainty.

Peshtigo fire

The Peshtigo fire, also called the Great Peshtigo Fire, was an 1871 firestorm in northeastern Wisconsin and Michigan that killed over 1,150 people, the deadliest wildfire in United States history.

Petrichor

Petrichor is the earthy scent produced when rain falls on dry soil, especially after a dry spell, named by two Australian CSIRO scientists in 1964.

Petrified wood

Petrified wood, also known as fossilwood or opalised wood, is fossilized vegetation in which minerals, usually silica, replace the organic material while preserving the wood's three-dimensional cellular structure.

Petrochronology

Petrochronology is the branch of geoscience that links radiometric dates on individual mineral zones to the specific rock-forming processes that produced them, combining isotopic dating with petrographic context.

Petrographic analysis

Petrographic analysis identifies minerals, textures, and modal composition in a rock by polarized-light microscopy of a thin section ground to a standard 30 µm thickness, a low-cost alternative to SEM and X-ray diffraction.

Petrography

Petrography is the systematic description and classification of rocks, most often by examining rock slices about 30 µm thick under a polarizing microscope; it is a subdiscipline of petrology, the broader science of rocks.

Petroleum

Petroleum, often called crude oil, is a naturally occurring mixture of hydrocarbons found underground, including crude oil, natural gas, and asphaltic compounds in tar sands and oil shales.

Petroleum play

A petroleum play is a set of oil and gas accumulations sharing similar geologic, geographic, and temporal properties, used as the working unit for exploration.

Petroleum system

A petroleum system, also called a hydrocarbon system, is a petroleum geology concept linking a source rock to the oil and gas it generated, formalized by Magoon and Dow in 1994.

Phanerozoic (Φανεροζωικός)

The Phanerozoic (Greek for "visible life") is the most recent eon of geologic time, running from 538.8 million years ago to the present and divided into the Paleozoic, Mesozoic, and Cenozoic eras.

Oct 22, 2026

Phase H

Phase H is a dense hydrous magnesium silicate, MgSiO4H2, stable at lower-mantle pressures and regarded as the deepest mineral able to carry subducted water into the deep mantle.