Geology is the group of sciences concerned with the study of the Earth,
including its structure, long-term history, composition, and origin.
This deals with the structure and composition of the Earth and the forces
of change altering them. The divisions that make up physical geology include
mineralogy (the arrangement of minerals),
petrology (the study of rocks and their combinations of minerals), geodesy,
and seismology (see earthquake). Much
of modern physical geology is based on the theory of plate
This deals with the Earth in past ages, and with the evolution of life upon
it. It embraces such sciences as paleoclimatology, paleomagnetism, paleontology, and stratigraphy, ; and relies heavily on
dating, events being related to the geological time scale, whose derivation
is primarily stratigraphical, to a lesser extent paleontological.
This lies between physical and historical geology, and borrows from both.
Concerned with the location and exploitation of the Earth's natural resources,
it is generally taken to include the disciplines of crystallography, mineralogy,
and petrology. Its practical manifestations are prospecting and mining.
Development of geology
Most early geological knowledge came from the experience of mining engineers,
some of the earliest geological treatises coming from the pen of Georgius
Agricola. The interest of the sixth century in fossils
was also reflected in the writings of K. von Genner. In the seventh century
the biblical timescale of about 6,000 years from the Creation to the present
largely constrained the many speculative "Theories of the Earth" that were
issued. The centuries most notable geological observations were made by
N. Steno. The late eighteenth century saw the celebrated controversy between Alfred
Wegener's "Neptunism" and J. Hutton's "Plutonists" as to the origin of the
rocks. The first decades of the nineteenth century, however, witnessed the decline
of speculative geology as field observations became ever more detailed.
William Smith (1769–1839), the "father of stratigraphy," show how
the succession of fossils could be used to index the stratigraphic column,
and he and others produced impressive geological maps. Charles Lyell's classic Principles of Geology
(1830–33) restated the Huttonian principle
of uniformitarianism and provided the groundwork for much of the later development
of the science. Louis Agassiz pointed to the importance of glacial action
in the recant history of the Earth (1840), while mining engineering continued
to contribute to the pool of geologic data. Among the most significant 20th
century developments in the earth sciences was the acceptance of plate
foreshadowed by Wegener's 1912 theory of continental