Earth, Age of

About 75 years ago, the best guess for the age of Earth was about 100 million years before the present. About 50 years ago, the best estimate was approximately 2 to 3 billion years. Now, the best estimate is that the earth was formed 4.75 billion years ago. In cosmic time, it may have taken another 14 billion years for the gases in the universe to coalesce into a liquid or plastic form. Scientific research and technological advancement improves with time, but how can such a huge amount of time be put into an understandable perspective? The archaeologist D. J. Mahony made an analogy with a walk down the avenue of time into the past, covering a thousand years at each step. The first step would take us back to the battle of Hastings, the second to the beginning of the Christian era, the third to Homeric Troy, the fourth to Abraham, and the seventh to the earliest traditional history of Babylon and Egypt. About a quarter mile would lead to the origin of the oldest stone tools found in Europe. To continue until we encountered the most ancient fossil organisms would mean a journey of more than 250 miles.

James Hutton, in the 18th century, was a farmer, a doctor, and, many believe, the father of modern geology. He perceived, from what he viewed and understood of the soils and the rocks, that the formation of the earth took a much longer period to happen than that postulated by Archbishop Ussher in the 17th century, who proposed that the earth was created on the evening of October 22, 4004 BCE. Charles Lyell, in the 19th century, using earlier works as well as his own observations, indicated that the earth was not only of great age but that its processes in the present could be used to illustrate the changes of the past. Early in the 20th century, Alfred Wegener presented the concept of continental drift, now known as plate tectonics, to his peers and to the world. These concepts by Hutton, Lyell, and Wegener were not readily accepted. But now we know that Pangea was truly a single continent about 200 million years ago and that that continent has become no fewer than six: Africa, Antarctica, Australia, Eurasia, North America, and South America. The geologic processes that we observe today have been recurring again and again. Some of these events and processes can be viewed in the geologic timescale in Table 1.

The study of Earth's origin is a work in progress. A multitude of geologists and other scientists for the past 500 hundred years or so have built the body of knowledge we have currently. Today, scientists are using new technologies to piece together how the earth was formed. It some ways, it is like building a structure from the top down, or as Hutton put it more than 200 years ago, “The present is the key to the past.” Speculation concerning Earth's origin and its formation runs rampant. This continues today regarding Earth's formation, but with developing technologies, new, vivid, and more exact evidence has begun to appear.

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