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In the 1700's belief in a 6000 year old Earth crumbled.Attempts to calculate the age of the Earth from physical considerations yielded estimates that ranged from 75,000 years (Buffon, 1774) to several billion years (de Maillet, Buffon).
It became clear that there had been significant changes in the Earth's topography over time and that these changes could neither be accounted for by natural processes operating during the brief nor by the postulated Noachian flood.Many authors choose to present the history of a complex subject by breaking it up into major threads and following the history of each thread separately.I have chosen instead to provide a chronology of significant works and their authors with a view to providing a sense of how perspectives on Geology changed over time.It was not ruled out, per se, but it was not necessary. In the new science, however, rational explanation was desirable. In 1640 Ussher produced his famous calculation that the Earth was created in 4004 BC.In 1637 Descartes produced a cosmogony that was highly influential for more than a century. It was not in their estimates of the age of the Earth - Descartes retained the biblical date.The physical models were open to question and, in retrospect, were naive. It became quite clear that many areas of the Earth had alternated between being land and being covered by seas, that there had been extensive slow sedimentation, that the mountains had not been created in situ as is but rather had a long history of slow deformation, and that long periods of erosion had shaped the Earth everywhere.
By the early 1800's it was generally accepted that the Earth had a long history. The uniformatarians (Hutton 1788, Lyell 1830) pictured the Earth as being indefinitely old.
The second is that the rates of the physical processes in question are variable and knowledge of them was incomplete.
In the late 1800's physicists, armed with a more advanced physics than that available to Descartes, made new estimates of the age of the Earth and the Sun.
There were various attempts to estimate the Earth's age, working back from sedimentation rates and other geophysical phenomena.
The attempts produced estimates from about 100 million years up to several billion years. The first is that the geological history was still being reconstructed.
Ussher accepted the Biblical account at face value, relying on the Biblical genealogies and on extant historical records.