5,021 articles
Oliver Fringer
Oliver Fringer is a Stanford professor who develops numerical models of coastal ocean, river, lake, and estuary dynamics, and received a PECASE award in 2008.
Olivine
Olivine, also known as crysolite, is a group of rock-forming silicate minerals ranging from forsterite to fayalite, usually olive green and dominant in Earth's upper mantle.
Olympic Dam
Olympic Dam is a poly-metallic underground mine in far northern South Australia, 650 km northwest of Adelaide, producing copper, uranium, gold, and silver for owner BHP.
Oman ophiolite
The Oman ophiolite, also called the Semail ophiolite, is the world's largest exposed slice of oceanic crust and mantle, covering about 20,000 km² in northern Oman and the UAE.
Omanago Group
Omanago Group (大真名子山) is a cluster of closely spaced dacitic lava domes in Nikko National Park, Tochigi Prefecture, Japan, built north of Nantai volcano, with a last known eruption around 3050 BCE.
Omayra Sánchez
Omayra Sánchez Garzón was a 13-year-old girl from Armero, Colombia, who died in November 1985 after roughly 60 hours trapped in debris from the Nevado del Ruiz lahar.
Ombrotrophic
Ombrotrophic describes a peatland, typically a bog, that receives all its water and dissolved nutrients from rain and snow, with no groundwater or runoff from mineral soil.
Omega equation
The omega equation is a diagnostic equation of quasi-geostrophic theory that determines vertical velocity in synoptic-scale atmospheric flow from geostrophic wind, pressure, and temperature fields, without time derivatives.
Onyx
Onyx is a banded variety of chalcedony, a microcrystalline form of quartz, whose straight parallel bands distinguish it from agate; black-and-white material is the classic form.
Oolite
Oolite is a sedimentary rock, usually limestone, composed of ooids, concentrically layered calcium carbonate grains under 2 mm that form in shallow, agitated seawater like the Bahamas.
Opal
Opal, historically called ceraunium, is a hydrated amorphous form of silica prized as a gemstone for its play-of-color, with Australia supplying about 95% of the world's precious opal.
Open-pit mining
Open-pit mining, also called opencast or open-cut mining, is a surface method that extracts near-surface ore from benches in a deepening pit; Utah's Bingham Canyon is a notable example.
OpenIFS
OpenIFS is a portable version of the Integrated Forecasting System (IFS), the European Centre for Medium-Range Weather Forecasts' global weather prediction model, launched in 2011.
Ophiolite
An ophiolite is a fragment of oceanic crust and underlying upper mantle thrust, or obducted, onto continental crust, occurring in all Phanerozoic mountain systems as fossil oceanic lithosphere.
Optically pumped magnetometer
An optically pumped magnetometer (OPM) is a magnetic field sensor that reads the Larmor precession of laser-pumped alkali vapor atoms, reaching femtotesla sensitivity comparable to SQUIDs.
Optically stimulated luminescence dating
Optically stimulated luminescence (OSL) dating determines how long buried quartz or feldspar grains have been hidden from daylight, dating sediments from one year to several hundred thousand years old.
Optimal fingerprinting
Optimal fingerprinting is a regression-based statistical method in climate science that detects climate change signals in observations and attributes them to forcings such as greenhouse gases.
ORAS5
ORAS5, or Ocean Reanalysis System 5, is ECMWF's fifth-generation global ocean and sea-ice reanalysis, operational since 2016, providing ocean and sea-ice initial conditions for all its coupled forecasting systems.
Ordos Basin
The Ordos Basin is a large sedimentary basin in the western North China Block, China, with a depositional history from the Mesoproterozoic to the Quaternary.
Ordovician
Ordovician Period, second Paleozoic period, 485.4–443.8 Ma (ICS), named by Lapworth; seven GSSP-defined stages, Great Ordovician Biodiversification Event, high CO2 with cooling, and the Hirnantian glaciation and mass extinction.
Ordovician–Silurian glaciation
The Ordovician–Silurian glaciation, often called the Hirnantian glaciation, was a brief, severe ice age about 445 million years ago that helped drive a major mass extinction.
Ore
Ore is naturally occurring rock or mineralized material that contains a valuable substance in sufficient concentration, and is accessible enough, to be mined and processed at a profit.
Ore microscopy and automated mineralogy
Ore microscopy examines polished ore sections under a microscope to identify minerals and textures; automated mineralogy performs the same characterization quantitatively using SEM-based imaging and X-ray analysis.
Oriented core
An oriented core is a cylindrical rock sample recovered by drilling whose original in situ position has been determined, typically by marking the core and measuring the mark's azimuth against geographic north.
Origin of water on Earth
The origin of water on Earth, also called the origin of the oceans, is the unsolved question of how Earth acquired its water, with asteroids the leading source.
Orogenic gold deposit
An orogenic gold deposit is gold mineralization deposited from low-salinity, aqueous-carbonic fluids rising along crustal faults during mountain building, supplying an estimated 75% of all gold extracted by humans.
Orogeny
Orogeny is the process by which mountain belts form, typically when tectonic plates collide or converge, folding and thickening the crust; examples include the Alps, Himalayas, and Appalachians.
Orographic lift
Orographic lift is the forced upward movement of air over rising terrain such as a mountain, cooling it and producing clouds and precipitation on the windward side.
Orpiment
Orpiment, also known as King's yellow or Auripigment, is a yellow arsenic sulfide mineral found in hydrothermal veins and hot springs, long used as a golden-yellow artist's pigment until abandoned for its toxicity.
Orthoclase
Orthoclase, also called orthoclase feldspar, is a rock-forming potassium feldspar mineral with the formula KAlSi₃O₈, common in granite and named in 1823 for its right-angle cleavage.