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Encyclopedia of Global Resources part 95 provides a wide variety of perspectives on both traditional and more recent views of Earth's resources. It serves as a bridge connecting the domains of resource exploitation, environmentalism, geology, and biology, and it explains their interrelationships in terms that students and other nonspecialists can understand. The articles in this set are extremely diverse, with articles covering soil, fisheries, forests, aluminum, the Industrial Revolution, the U.S. Department of the Interior, the hydrologic cycle, glass, and placer mineral deposits. . | 868 Oil and natural gas formation Global Resources the air so that decay by biological means or reaction to oxygen will not destroy it. Deposition and Transformation Microscopic plant and animal life is abundant in much of the oceans. When these organisms die their remains usually settle to the seafloor. When this takes place in near-shore marine environments such as on continental shelves or where large rivers form marine deltas sediments derived from continental erosion accumulate rapidly. In such a setting the initial requirements for the formation of oil are satisfied An abundance of organic matter is rapidly buried by sediment so that it is free from aerobic and biological contamination. The majority of oil and natural gas deposits are believed to have been formed by such accumulated marine organisms. Oil fields reflect the presence of prehistoric marine environments that now exist below the surface as marine deposited sedimentar y rocks. As sedimentar y deposition continues to bury the organic matter it begins to change into a solid organic material called kerogen. At relatively low temperatures and shallow burial depths kerogen is chemically inert. Kerogen consists primarily of hydrocarbons that are in the solid state and that are insoluble not only in water but also in a variety of organic solvents. Kerogen from the lower plants and animals with a high lipid content and a relatively high hydrogen ratio will produce oil. Kerogen from the higher vascular plants is lower in hydrogen content and will produce only gas. As pressures increase from the weight of continued deposition of overlying sediment the sediments are gradually transformed into lithified rock. Temperatures increase with depth below the Earth s surface slowly over long periods of time chemical reactions take place. These reactions break down the large complex organic molecules into simpler smaller hydrocarbon molecules. The nature of the hydrocarbon changes with time and continued heat and .
