Geology Geomorphology and Geography

Geology, geomorphology, and geography are all scientific disciplines that study the earth. At first glance these three disciplines may seem separate and easily distinguishable from one another. As you read on, however, you will find that the overlap is considerable, and in many instances one cannot be exactly sure of which discipline a particular subject pertains to.

Geology is the study of many aspects of the earth, but it does not include meteorology, climatology, oceanography, geochemistry, or geophysics—although elements of geology are part of them, and they are part of geology. All of these disciplines and others are included in the more general study, the "earth sciences." Geology can also be thought of as the study of the solid earth and its complex interaction between air (atmosphere), water (hydrosphere), and life (biosphere).

Geology can be best described as a science that explains how the earth works, the changes that take place on the earth, and the reasons for the changes. Plate tectonics is the theory that ties many geologic phenomena together and explains how the earth operates. Basic to the science of geology is the principle of uni-formitarianism—the assumption that the so-called laws of nature have not changed over time. Geologists apply the principle to rocks of any age. By examining processes going on

Geologists at work. Geology can be described as a science that explains how the earth works, the changes that take place on the earth, and the reasons for the changes. (USGS/CVO)

today and their results—the structure of sand dunes, for example—a geologist who sees the same structure in ancient rocks assumes that they are also sand dunes. Examining rocks erupted from volcanoes can indicate that ancient rocks were volcanic, even though traces of the volcano itself have been eroded away. Geologists like to use the phrase "the present is the key to the past" to describe these procedures concisely. In actuality, this is true for the most part, but there are events that have occurred in the past that have not yet occurred during historical times. For example, the large impact of a meteorite may have caused dinosaurs to become extinct. For historical reasons, because it was part of the early development of modern geology, geologists like to keep using the term uniformitarianism, but in reality it is just another name for the sci entific method. The study of geology leads to a greater appreciation of science in general and the origin of materials we need for our survival, comfort, and pleasure; it also helps us to understand how demands for these materials affect the environment and the balance of nature, and ultimately people on earth.

Geology is divided into a number of specific branches that study the composition of the earth (mineralogy, petrology, petrography); the structure of deformed rocks (tectonics, structural geology); the history of the earth and its life (historical geology); the physical properties of the earth, earthquakes, and their effects (seismology); volcanism (volcanology); landforms and the processes that produce them (geomorphology); fossils and ancient life (paleontology); and sediments and sedimentary rocks, their origin and age (petrology, stratigraphy). Geology also draws on many other disciples, including chemistry, physics, mathematics, and biology.

Many geological changes occur at a very slow rate, some not even observable on a human time scale, making it very difficult to demonstrate how certain materials or features were formed. At the other end of the scale, some features are too large to duplicate in a lab—thus geologists compromise by creating scale models.

Geology also has a practical side. Everything we have and use on earth (excepting meteorites) comes from rocks, plants, or animals. Geologists explore the earth for economically important substances such as metallic ores, sand and gravel deposits, coal, oil, and gas. Equally important is the search to find a way to predict volcanic eruptions and earthquakes.

Geomorphology is the discipline concerned with the shape of the landscape and the processes that create it, their description and classification; it is usually considered a part of the geological sciences. It also includes the study of submarine features, and some scientists extend it to the study of planetary landscapes. Landforms are discrete or individual features, like a volcano or a valley. Landscapes are an assemblage of landforms that are created by complex, climate-controlled processes. Geomorphologists study the relationships between landforms and the processes currently acting upon them. Geomorphology is also a historical science, because it is necessary to consider past events that help shape the landscape. As is the case in many other sciences, geomorphology is interwoven with other sciences, inasmuch as it involves the atmosphere, hydrosphere, and biosphere, physics and chemistry. The erosional response of the surface to uplift falls in the realm of geophysics, which is concerned with the mechanics and rates of uplift. How much sediment a stream carries is included in hydrology, which measures the frequency and intensity of flooding. Pedology, the science of soils, involves the effects of soil properties on slope stability, which, applied to geomorphology, makes a contribution to topography and soil-forming processes. On a smaller scale, geomorphol-ogy is concerned with how topography controls plant growth (biology) on the microenvi-ronmental level, and the role that vegetation cover plays in affecting slope stability.

Geography is defined as the study of the earth's surface. Although it is usually associated with maps and map-making, it is a much broader discipline; although maps are an important tool used by geographers (as well as geologists), they are a small part of the subject. Geography describes and analyzes the spatial variations in physical, biological, and human phenomena that occur together on the surface of the earth, and it deals with their interrelationships and their local and regional patterns. It is especially concerned with human utilization of natural resources and with the impact of human activities on the environment. Included in human geography is the study of the distribution of population and the religions of people, and the varieties of designs of cities, road systems, and dams. Physical geography is the observing, measuring, and describing of the earth's surface, and some geographers include geomorphology, climatology, biogeography, and soil distribution as branches of this subdivision of geography. Therefore, geography is a broad-ranging discipline that involves the discerning of patterns of anything on the surface of the earth that involves both natural and human features, including economic and political activities. Geographers therefore are knowledgeable about the earth sciences, biology, and sociology, making their subject interdisciplinary.

—Sidney Horenstein

See also: Climatology; Geological Time Scale; Hutton, James; Meteorology; Plate Tectonics

Bibliography

Bloom, Arthur L. 1991. Geomorphology, 2d ed. Engle-wood Cliffs, NJ: Prentice Hall; Laing, David. 1991. The Earth System: An Introduction to Earth Science. Dubuque, IA: Wm. C. Brown; Plummer, Charles C., David McGeary, and Diane Carlson. 2002. Physical Geology, 9th ed. New York: McGraw-Hill; Strahler, Alan H., and Arthur N. Strahler. 1998. Introduction to Physical Geography, 2d ed. New York: John Wiley and Sons.

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