Geology

Geology is the study of the solid, nonliving earth, including earth's materials, structure, processes, and history. Earth's nonliving materials and features are the result of geologic processes. Geologists study these processes, operating today, and in doing so interpret how ancient earth materials or features formed. By determining these processes, and the time at which they occurred, geologists interpret the history of the earth. The science of geology includes the following subdisciplines: mineralogy, the study of minerals; petrology, the study of rocks and their formation; geomorphology, the study of earth surface processes and landform development; sedimentology and stratigraphy, the study of sediment and strata; paleontology, the study of fossils and ancient life; structural geology, the study of rock deformation; geophysics, physics of the earth; and geochemistry, chemistry of the earth.

To environmental science, geology provides the knowledge base for several basic areas of study. Geology includes the study of geologic time and earth history. Information about ancient (prehuman) earth and its atmosphere, hydrosphere, environments, and geologic processes, is preserved in the rock record. Geologists interpret the information in the rocks and provide analyses of earth's ancient conditions. For example, information about the Precambrian atmosphere is interpreted from mineral assemblages and fossils contained in Precambrian strata. Similarly, the long-term record of global climate change, including global warming and cooling, is preserved in the rock record.

Geologic maps portray the surface occurrence of different types of rocks. These maps are the result of careful ground-based investigations. Geologic maps provide the locations of different rocks and sediment deposits on earth's surface. They can be used to predict the suitability of various places for different types of land use, and to show the surface occurrence of mineral and energy resources.

Geologic maps are also used, sometimes in conjunction with subsurface information obtained through drilling and geophysical methods, to interpret the location and structural geometry of rocks in the subsurface. Such information is used to find and assess the occurrence of mineral and energy resources [Page 755]in the subsurface. In addition, these configurations, together with information about the permeability of the rocks, control the presence and movement of subsurface fluids such as groundwater, oil or natural gas. For example, the direction and speed of groundwater flow, including any contaminants, may be predicted by understanding the nature and geometry of rocks in the subsurface.

Information about the surface and subsurface occurrence of rocks, sediments, and minerals is also important to the extent that these materials interact with water or other fluids. Through the process of weathering, bedrock contributes solid and dissolved constituents to groundwater, surface water and soils. These constituents may constitute basic nutrients or contaminants, depending on the constituent and its concentration. Some subsurface materials—such as sand or sandstone—may act as a natural filter, removing particulate matter and thereby purifying groundwater.