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Geologic Time

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Dating the Earth

How do we know how old everything is? Prior to the late 17th century, geologic time was thought to be the same as historical time. That is, until James Ussher came along.

Archbishop James Ussher of Armagh, Ireland (1581-1656). Ussher was highly intelligent and spoke many languages. He is known for his work, the "Annals of the Old Testament, deduced from the first origins of the world", in which he determined that Earth formed on October 23, 4004 BCE. How did he come up with this date? Research, research, and more research. Ussher used not only the Old Testiment, but also works from the Persians, Greeks and Romans, astronomy, and ancient calendars. While it is temping to poo-poo this date, Ussher's work was revolutionary at the time and set the stage for others to follow.

Nicolaus Steno (1638–1686) – Danish physician and later a Catholic Bishop. While in Italy, Steno was asked by Ferdinando II de' Medici, Grand Duke of Tuscany (yes, THAT de'Medici family) to study a shark's head that had been caught off the coast of Livorno. Steno observed that the teeth looked much like those found embedded in rocks nearby. He questioned the origin of items like these; the current hypothesis was that fossils 'grew' in the rocks. In 1669, Steno published 'De solido intra solidum naturaliter contento dissertationis prodromus", or "Preliminary discourse to a dissertation on a solid body naturally contained within a solid", in which he suggested, among other things, that lithification and uplift happed over long periods of time.

James Hutton (1726-1797) – Hutton was a Scottish physician and naturalist. He is called “the Father of Modern Geology”, as his work estabilished geology as a science of it's own. Though years of observation and research, Hutton realized that geologic processes are constantly shaping our planet. This idea lead to the “Principle of Uniformitarianism”, or, the present is the key to the past. This means that the same geologic processes that are occuring today have done so in the same manner in the past, and will continue to do so in the future. Of the abyss of time, Hutton wrote: “we find no vestige of a beginning; no prospect of an end.”

William “Strata” Smith (1769 - 1839) – an English Geologist (!), Smith was the first to note that strata could be matched across distances. He is also credited with making the 1st Geologic map of England.




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CSULA Department of Geosciences and the Environment
Pasadena City College Department of Geology    
    © Sonjia Leyva 2018