Geology

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Geochemistry

Geochemistry is the application of chemistry to the study of the earth, its materials, and the cycling of chemicals through its systems. It is essential in numerical dating and in reconstructing past conditions on the earth. Geochemistry is important for tracing the transport of chemicals through the earth’s four component systems: the lithosphere (rocky exterior), the hydrosphere (waters of the earth), the atmosphere (air), and the biosphere (the system of living things). Biogeochemistry is an emerging field that examines the chemical interactions between living and nonliving systems—for example, microorganisms that act in soil formation. Geochemistry has important applications in environmental and economic geology as well as in the fields of mineralogy and petrology.

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Mineralogy and Petrology

The fields of mineralogy (the study of minerals) and petrology (the study of rocks) are closely related because rocks are made of minerals. Mineralogists and petrologists study the origin, occurrence, structure, and history of rocks or minerals. They attempt to understand the physical, chemical, and less commonly, biological conditions under which geologic materials form. Mineralogy is important for understanding natural materials and is also used in the materials engineering field, such as in ceramics. Petrology focuses on two of the three rock types: igneous rocks—rocks made from molten material—and metamorphic rocks—those rocks that have been changed by high temperatures or pressures. The third rock type, sedimentary rocks, are the focus of sedimentary geology, commonly classified under historical geology.

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Structural Geology

Structural geology deals with the form, arrangement, and internal structure of rocks, including their history of deformation, such as folding and faulting. Structural geology includes everything from field mapping to the study of microscopic deformation within rocks. Most geologic reconstructions require an understanding of structural geology. The term tectonics is commonly used for large-scale structural geology, such as the study of the history of a mountain belt, or plate tectonics (the study of the crustal plates). Neotectonics is the study of recent faulting and deformation; such studies can reconstruct the history of active faults, and the history can be used in hazard analysis and land-use planning.

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Hydrology and Geomorphology

The earth's surface processes are the focus of hydrology and geomorphology. Hydrology is the study of water on the earth's surface, excluding the oceans. Hydrogeology is the study of groundwater (water under the ground) and the geologic processes of surface water. As water is necessary for life, hydrology and hydrogeology are important for economic and environmental reasons, such as maintaining a clean water supply. Geomorphology is the examination of the development of present landforms; geomorphologists attempt to understand the nature and origin of these landforms. They may work from the large scale of mountain belts to the small scale of rill marks (small grooves in sand). Geomorphologists commonly specialize in one of many areas, such as in glacial or periglacial (near glaciers), fluvial (river), hillslope, or coastal processes. Their work is important for a basic understanding of the active surface that humans live on, a surface that is subject to erosion, landslides, floods, and other processes that affect our daily lives.

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Marine Geology

Geology specific to the ocean environment is called marine geology. Marine geologists may be specialists in a number of fields, including petrology, sedimentology, stratigraphy, paleontology, geochemistry, geophysics, and volcanology. They may take samples from the ocean while out at sea or make measurements through remote sensing techniques. Drilling platforms and drilling ships allow earth scientists to make more-detailed studies of the history of the oceans and the ocean floor. For example, in 1984 an international team of geoscientists from 20 nations formed the Ocean Drilling Program, an outgrowth of the earlier Deep Sea Drilling Program. This program is designed to set up drilling through the top sedimentary layer and the ocean crust in deep-sea sites around the world. This work has helped the field of paleoceanography (the reconstruction of the history of the oceans, including ancient ocean chemistry, temperature, circulation, and biology). See also Ocean and Oceanography.