GEOLOGY

scientific study of the Earth, including its composition, structure, physical properties, and history. The term geology is broadly inclusive and is often regarded as embracing all of the geologic sciences. Geology is commonly divided into a number of subdisciplines: (1) those concerned with the chemical makeup of the solid Earth, which include the study of minerals (mineralogy) and rocks (petrology); (2) those having to do with the structure of the solid Earth, as, for example, the study of the relationships of rocks and geologic features in general (structural geology) and the science of volcanic phenomena (volcanology); (3) those concerned with landforms and the processes that produce them (geomorphology and glacial geology); (4) those dealing with geologic history, including the study of fossils and the fossil record (paleontology), the development of sedimentary strata (stratigraphy), and the evolution of planetary bodies and their satellites (astrogeology); and (5) economic geology and its various branches e.g., mining geology and petroleum geology. Some major fields closely allied to geology are geodesy, geophysics, and geochemistry. The various subdisciplines of geology not only intergrade with one another but also with other branches of the Earth sciences and with such fields as physics, chemistry, biology, and mathematics. Paleontology, for instance, at times requires the use of organic chemistry, physical chemistry, and statistics. The statistical analysis of data also is an important facet of geomorphology and stratigraphy, as is the use of mathematical models. Besides providing a better understanding of the Earth's evolution and its present features, geology serves society in a variety of practical ways. Exploration for deposits of commercially valuable minerals is broadly guided by geologic principles and conducted with geophysical and geochemical methods. The search for fossil fuels (coal, oil, and natural gas) is strongly influenced by those aspects of geology dealing with the deposition and deformation of sedimentary rocks and with the flow of underground fluids. Significant, too, is the contribution of seismological research, whose findings have enabled engineers to design structures that are better able to withstand earthquakes.