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Researchers at Duke University in North Carolina (United States) have developed a test for distinguishing lead isotopes found in coal fly ash from lead isotopes found in other lead-containing sources, such as paint. Fly ash is a fine particulate…

The harvest of animals and plants from the ocean to provide food for people and animals. Important products in marine capture fisheries include fish (Fig. 1); mollusks such as oysters, clams, and squid; and crustaceans such as crabs and shrimps.…

A combustible gas that occurs beneath the surface of the earth, often found in conjunction with petroleum deposits. Its main use is for fuel, but it is also used to make carbon black, certain chemicals, and liquefied petroleum gas. Liquefied…

Solid, icelike combinations of water and natural gas. Gas hydrates occur wherever appropriately-sized gases and water are brought together in sufficient quantities under specific conditions of low temperature and moderately high pressure. Prior to…

The natural biological and chemical processes through which inorganic and organic nitrogen are interconverted. It includes the processes of ammonification, ammonia assimilation, nitrification, nitrate assimilation, nitrogen fixation, and…

One of the major subdivisions of the interconnected body of salt water that occupies almost three-quarters of the Earth’s surface. Earth is the only planet in the solar system whose surface is covered with significant quantities of water (Fig. 1).…

The decrease in the pH of the ocean over time, as carbon dioxide (CO2) from the atmosphere is absorbed by and dissolves in seawater. Since the Industrial Revolution, rising carbon dioxide levels in the atmosphere and increased absorption of CO2 by…

A technique of selective chemical etching to reveal tracks of heavy nuclear particles in a wide variety of solid substances. Developed in order to see fossil particle tracks in extraterrestrial materials, the technique finds application in many…

Any mollusk-formed calcareous concretion that displays an orient and is lustrous. There are two major groups of bivalved mollusks in which gem pearls (see illustration) may form: the saltwater pearl oyster, of which there are several species…

A dark-brown or black residuum produced by the partial decomposition and disintegration of mosses, sedges, trees, and other plants that grow in marshes and other wet places. Forest-type peat, when buried and subjected to geological influences of…

A mineral inosilicate with composition Ca2NaSi3­O8 (OH), crystallizing in the triclinic system. Crystals are usually acicular in radiating aggregates (see illustration). There is perfect cleavage parallel to the front and basal pinacoids yielding…

Exceptionally coarse-grained and relatively light-colored crystalline rock composed chiefly of minerals found in ordinary igneous rocks. Extreme variations in grain size also are characteristic (Fig. 1), and close associations with dominantly…

The younger subperiod of the Carboniferous. The Pennsylvanian derives its name from a thick succession of mostly nonmarine, coal-bearing strata in Pennsylvania, United States. Radiometric ages place the beginning of the Pennsylvanian at…

A mineral having composition (Fe,Ni)9S8. Pentlandite is the major ore of nickel. It crystallizes in the isometric system, but crystals are rare. It is usually massive, showing a well-defined octahedral parting. The hardness is 3.5–4 (Mohs scale) and…

A rock consisting of more than 90% of millimeter-to-centimeter-sized crystals of olivine, pyroxene, and hornblende, with more than 40% olivine. Other minerals are mainly plagioclase, chromite, and garnet. Much of the volume of the Earth's mantle…

A naturally occurring complex liquid hydrocarbon found in source rocks beneath the Earth’s surface which, after distillation, yields combustible fuels, petrochemicals, and lubricants; also known as crude oil. Strictly speaking, petroleum consists…

The extent to which a plant, or plant ecosystem, is susceptible to, or unable to cope with, the adverse effects of climate change. Plants are constantly changing their ecophysiology and distributions over different timescales as they respond to…

A method of obtaining age estimates on organic materials which has been used to date samples as old as 75,000 years. The method was developed in the late 1940s by Willard F. Libby and coworkers, and has provided age determinations in archeology,…

A rigid and wave-resistant marine structure that stands above its surroundings. To navigators, a reef is any rocky structure that poses a threat to navigation. Marine biologists and geologists specify that reefs are constructed by organisms that…

The recording of information about objects by the use of a device not in physical contact with the object. The word remote is derived from the Latin word remotus and describes an object situated at some distance away. Remote-sensing (RS) devices are…

The noxious mixture of gases and particles commonly associated with air pollution in urban areas.The term smog is a contraction of smoke and fog. Air pollutionThe only characteristic of smog that is readily apparent to the unaided observer is the…

The electromagnetic radiation and particles (electrons, protons, alpha particles, and rarer heavy atomic nuclei) emitted by the Sun. The electromagnetic radiation (light) that shines from the Sun covers a wavelength range from x-rays to radio waves,…

A series of long waves generated by underwater earthquakes, landslides, slumps, volcanic eruptions, meteorological events, and asteroid impacts that violently flood adjacent and distant coastlines and coastal communities, with devastating impact.…