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Some of the most important discoveries of modern science and technology has been the discovery of the Earth's age and the vast length of time encompassed by it's history. This scale, comprised of billions and trillions of years is called the geologic time.
Most cultures incorporate some form of creation mythology, for example, the biblical Book of Genesis. In the mid-17th century an Irish clergyman, Bishop James Usher, added the years in the biblical genealogies and concluded that the Earth was created in 4004 BC. This idea persisted for a long while, although the 18th-century French scientist Georges Louis Leclerc, Comte de Buffon, reasoned that the Earth cooled from an originally molten body and that this would have required at least 75,000 years.
Buffon had to recant, but development of the principle of uniformitarianism in the late 1700s and early 1800s provided geologists with new grounds for arguing that the Earth is far older than anyone had imagined.
Similarly, in 1859, Charles Darwin recognized that millions of years were necessary for small evolutionary changes to accumulate and produce the variety of life we see today. Because they lacked definitive, precise data, however, 19th-century geologists could only guess at the age of the Earth. In the meantime, an accurate, relative geologic time scale had been developed, which placed the main events of geologic history in their proper sequence.
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