Geologic Time

One of the most important discoveries of modern science has been the age of the Earth and the vast length of time encompassed by its history. The scale of this history, in the millions and billions of years, is recognized as geologic time.

Most cultures incorporate some form of creation mythology, for example, the biblical Book of Genesis. In the mid 17th century an Irish churchman Bishop James Ussher 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 geologist with new grounds for arguing that the Earth a far older than anyone had imagined.

Similarly, in 1859, Charles Darwins recognized that millions of years were necessary for small evolutionary changes to accumulate and produce the variety of life we see today. Because the lacked definitive, precise data, however, 19th century geologiest 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 proper sequence.