The study of the physical material of the Earth dates back at least to ancient Greece when Theophrastus (372-287 BCE) wrote the work Peri Lithon (On Stones). In the Roman period, Pliny the Elder wrote in detail of the many minerals and metals then in practical use, and correctly noted the origin of amber.
Some modern scholars, such as Fielding H. Garrison, are of the opinion that modern geology began in the medieval Islamic world. Abu al-Rayhan al-Biruni (973Ц1048 CE) was one of the earliest Muslim geologists, whose works included the earliest writings on the geology of India, hypothesizing that the Indian subcontinent was once a sea. Islamic Scholar Ibn Sina (Avicenna, 981Ц1037) proposed detailed explanations for the formation of mountains, the origin of earthquakes, and other topics central to modern Geology, which provided an essential foundation for the later development of the science. In China, the polymath Shen Kuo (1031Ц1095) formulated a hypothesis for the process of land formation: based on his observation of fossil animal shells in a geological stratum in a mountain hundreds of miles from the ocean, he inferred that the land was formed by erosion of the mountains and by deposition of silt.
Nicolas Steno (1638Ц1686) is credited with the law of superposition, the principle of original horizontality, and the principle of lateral continuity: three defining principles of stratigraphy.
The word geology was first used by Ulisse Aldrovandi in 1603, then by Jean-André Deluc in 1778 and introduced as a fixed term byHorace-Bénédict de Saussure in 1779. The word is derived from the Greek γῆ, gê, meaning "earth" and λόγος, logos, meaning "speech". But according to another source, the word "Geology" comes from the Norwegian, Mikkel Pedersøn Escholt (1600Ц1699), who was a priest and scholar. Escholt first used the definition in his book titled, Geologica Norvegica (1657).
William Smith (1769Ц1839) drew some of the first geological maps and began the process of ordering rock strata (layers) by examining the fossils contained in them.
James Hutton is often viewed as the first modern geologist. In 1785 he presented a paper entitled Theory of the Earth to the Royal Society of Edinburgh. In his paper, he explained his theory that the Earth must be much older than had previously been supposed in order to allow enough time for mountains to be eroded and for sediments to form new rocks at the bottom of the sea, which in turn were raised up to become dry land. Hutton published a two-volume version of his ideas in 1795.
Followers of Hutton were known as Plutonists because they believed that some rocks were formed byvulcanism, which is the deposition of lava from volcanoes, as opposed to the Neptunists, led by Abraham Werner, who believed that all rocks had settled out of a large ocean whose level gradually dropped over time.
Sir Charles Lyell first published his famous book, Principles of Geology, in 1830. The book, which influenced the thought of Charles Darwin, successfully promoted the doctrine of uniformitarianism. This theory states that slow geological processes have occurred throughout the Earth's history and are still occurring today. In contrast, catastrophism is the theory that Earth's features formed in single, catastrophic events and remained unchanged thereafter. Though Hutton believed in uniformitarianism, the idea was not widely accepted at the time.
Much of 19th-century geology revolved around the question of the Earth's exact age. Estimates varied from a few 100,000 to billions of years. By the early 20th century, radiometric dating allowed the Earth's age to be estimated at two billion years. The awareness of this vast amount of time opened the door to new theories about the processes that shaped the planet. The most significant advances in 20th century geology have been the development of the theory of plate tectonics in the 1960s, and the refinement of estimates of the planet's age. Plate tectonic theory arose out of two separate geological observations: seafloor spreading and continental drift. The theory revolutionized the Earth sciences. Today the Earth is known to be approximately 4.5 billion years old.