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Geology is the study of the earth. Geology tries to explain how the earth was formed and how it changes. Scientists called geologists study rocks, soils, mountains, rivers, oceans, caves, and other parts of the earth.
There are two main fields of geology: physical geology and historical geology. Physical geology is the study of the materials that make up the earth, and the forces that shape the earth. Historical geology deals with the history of the earth. Many problems are a part of both fields, and physical and historical geology are usually studied together.
Historical Geology is the study of rocks to seek changes to the earth and life on it through time and space. The changes could be due to to many natural events as meteorite impacts, volcanic eruptions, earthquakes, erosion, slow movement of continents, climatic changes etc. Evidence of all these events are preserved in the geologic records i.e. rock units.
The oldest meteorites and oldest moon rocks are 4.6 billion years old. Testing these rocks for radioactive materials i.e. radiometric dating, determine age of these rock samples. Many radioactive elements can be used as geologic clocks. Each radioactive element decays at its won constant rate. Once this rate is known, geologists can measure length of time over which decay has been occurring. A Mass Spectrometer measures amount of various isotopes present in especially prepared samples of rocks.
Historical geology is one of the two major divisions in the study of geology. The other major division is physical geology. Historical geology includes the physical, chemical, and biological history of the earth.
Geologists study rock formations and the fossil record to gain information about the geologic history of the earth. Historical geology uses the principle of uniformitarianism to interpret the geologists' data. The principle of uniformitarianism states physical and chemical processes that produce rock formations and fossils have been similar throughout history but the process rates can vary. This means that geologists can use information from recent geological events to understand how the historical geological record was formed.
Historical geology is often represented by the geologic time scale. The geologic time scale places the major events of the earth's evolution in chronological order. The units of geologic time scale are the geologic eon, era, period, and epoch. Eon is the largest unit and epoch is the smallest.
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