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The Age of the Earth

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Summarize advances over time in determining the age of the Earth, including the importance of the discovery or radioactivity.

* Scientists have settled on the age of the earth to be 4.5 to 4.6 billion years as a result of research started many years ago. This conclusion was based upon carefully designed and conducted experiments. For thousands of years people have been trying to compute how old the earth is. According to Dr. Michael E. Wysession, the first documented case in determining how old the earth was traces back to 450 B.C. A man called Herodotus had Egyptians dig trenches along the Nile River so he could count the layers. He was able to identify 5,000 different layers and he therefore suggested that the earth was at least 5,000 years old. In 1625 Archbishop James Ussher determined that the Earth was created in the year 4004 B.C. His determination was made by counting back generations in the Bible. This would make the earth 6,000 years old. In the 18 to 19 century Earth's scientist began to realize that the Earth was much older than the previous estimation. The most significant calculation was by the famous English physicist William Thompson who became known as Lord Kelvin. Lord Kelvin's estimation derived in 1862, he calculated from the rate at which Earth loses heat that Earth must have been entirely molten between 98 million years old. Thirty-five years later he redid that calculation and computed that the age of Earth was between 20 and 40 million years old. As smart as Lord Kelvin was he was dramatically wrong seating back scientist and geologist years. With the popularization of Uniformitarianism by the works of James Hutton and Charles Lyell; uniformitarianism paved the way for new fields of studies such as biological evolution. The uniformitarianism concept, along with its mandatory accompanying old earth philosophy, provided the primary influence for Charles Darwin and his theory of evolution. The discovery of radioactivity invalidated Lord Kelvin's claim because it provided a heat source that he had not known about. Henri Becquerel discovery of radioactivity in 1896 revealed that when radioactive elements decay, heat is given off and the heat is added to the heat already in the Earth. The amount of radioactive heat given off at present approximates the heat Earth is losing. The discovery of radioactivity also provided the means to determine how old the Earth is by dating the ages of rocks. Radiometric dating uses a naturally occurring radioactive element that is simple in concept even though technically complex. If we know the number of radioactive parent atoms present when a rock formed and the number present now, scientist can calculate the age of the rock using the decay constant. Earth is now regarded as between 4.5 and 4.6 billion years old; the age determination comes primarily from dates obtained from meteorites and lunar rocks. The methods of dating meteorites



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