<P> Geology existed as a cloud of isolated, disconnected ideas about rocks, minerals, and landforms long before it became a coherent science . Theophrastus' work on rocks, Peri lithōn, remained authoritative for millennia: its interpretation of fossils was not overturned until after the Scientific Revolution . Chinese polymath Shen Kua (1031--1095) first formulated hypotheses for the process of land formation . Based on his observation of fossils in a geological stratum in a mountain hundreds of miles from the ocean, he deduced that the land was formed by erosion of the mountains and by deposition of silt . </P> <P> Geology did not undergo systematic restructuring during the Scientific Revolution, but individual theorists made important contributions . Robert Hooke, for example, formulated a theory of earthquakes, and Nicholas Steno developed the theory of superposition and argued that fossils were the remains of once - living creatures . Beginning with Thomas Burnet's Sacred Theory of the Earth in 1681, natural philosophers began to explore the idea that the Earth had changed over time . Burnet and his contemporaries interpreted Earth's past in terms of events described in the Bible, but their work laid the intellectual foundations for secular interpretations of Earth history . </P> <P> Modern geology, like modern chemistry, gradually evolved during the 18th and early 19th centuries . Benoît de Maillet and the Comte de Buffon saw the Earth as much older than the 6,000 years envisioned by biblical scholars . Jean - Étienne Guettard and Nicolas Desmarest hiked central France and recorded their observations on some of the first geological maps . Aided by chemical experimentation, naturalists such as Scotland's John Walker, Sweden's Torbern Bergman, and Germany's Abraham Werner created comprehensive classification systems for rocks and minerals--a collective achievement that transformed geology into a cutting edge field by the end of the eighteenth century . These early geologists also proposed a generalized interpretations of Earth history that led James Hutton, Georges Cuvier and Alexandre Brongniart, following in the steps of Steno, to argue that layers of rock could be dated by the fossils they contained: a principle first applied to the geology of the Paris Basin . The use of index fossils became a powerful tool for making geological maps, because it allowed geologists to correlate the rocks in one locality with those of similar age in other, distant localities . Over the first half of the 19th century, geologists such as Charles Lyell, Adam Sedgwick, and Roderick Murchison applied the new technique to rocks throughout Europe and eastern North America, setting the stage for more detailed, government - funded mapping projects in later decades . </P> <P> Midway through the 19th century, the focus of geology shifted from description and classification to attempts to understand how the surface of the Earth had changed . The first comprehensive theories of mountain building were proposed during this period, as were the first modern theories of earthquakes and volcanoes . Louis Agassiz and others established the reality of continent - covering ice ages, and "fluvialists" like Andrew Crombie Ramsay argued that river valleys were formed, over millions of years by the rivers that flow through them . After the discovery of radioactivity, radiometric dating methods were developed, starting in the 20th century . Alfred Wegener's theory of "continental drift" was widely dismissed when he proposed it in the 1910s, but new data gathered in the 1950s and 1960s led to the theory of plate tectonics, which provided a plausible mechanism for it . Plate tectonics also provided a unified explanation for a wide range of seemingly unrelated geological phenomena . Since 1970 it has served as the unifying principle in geology . </P>

When did oceanography begin to develop as a modern science