Thursday, November 15, 2012

Early Attempts at Calculating the Age of the Earth

'Before the world came into being there existed only the Cosmic Egg that floated unchanging in the Void for untold ages. Yin and Yang was the Egg, opposites perfectly mingled. And it was because they were perfectly mingled that the world could not yet be.

'Then within the Egg was born P'an Ku, the primordial man who slowly grew and grew until the Egg felt too cramped for him. Impatiently he stretched out his limbs and his hand closed about an axe, coming from whence no one knows. Striking with all his might, P'an Ku split the shell of the Egg and burst free.

'He then began to fashion the material of Chaos, separating Yin and Yang into sky and earth, in which he was aided by the four most fortunate creatures who had emerged from the Egg with him: the Unicorn, the Dragon, the Phoenix and the Tortoise. They were engaged in this labour for 18,000 years and each day P'an Ku grew ten feet, using his own body as a pillar to force heaven and earth apart.

'When the separation was complete and they had settled in their places, P'an Ku died. His breath became the wind and clouds, his eyes became the sun and moon. His stomach, head and limbs became the principal mountains of the world, watered by the rivers of his sweat and tears; his flesh became the fertile soil and his hair the plants and trees which took root in it. The fleas on his body became the human race. Then P'an Ku drifted in space for a further 18,000 years before entering a holy virgin as a ray of light and being born into the world by her as Tien-Tsun, the First Cause.'

Historically, the subdivision of Precambrian rock sequences (and, therefore, Precambrian time) had been accomplished on the basis of structural or lithologic grounds. With only minor indications of fossil occurrence (mainly in the form of algal stromatolites), no effective method of quantifying this loosely constructed chronology existed until the discovery of radioactivity enabled dating procedures to be applied directly to the rocks in question.

The quantification of geologic time remained an elusive matter for most human enquiry into the age of the Earth and its complex physical and biological history. Although Hindu teachings accept a very ancient origin for the Earth, medieval Western concepts of Earth history were based for the most part on a literal interpretation of Old Testament references. Biblical scholars of Renaissance Europe and later considered paternity as a viable method by which the age of the Earth since its creation could be determined. A number of attempts at using the "begat" method of determining the antiquity of an event-essentially counting backward in time through each documented human generation-led to the age of the Earth being calculated at several thousand years. One such attempt was made by Archbishop James Ussher of Ireland, who in 1650 determined that the Creation had occurred during the evening of Oct. 22, 4004 BCE. By his analysis of biblical genealogies, the Earth was not even 6,000 years old! 

From the time of Hutton's refinement of uniformitarianism, the principle found wide application in various attempts to calculate the age of the Earth. As previously noted, fundamental to the principle was the premise that various Earth processes of the past operated in much the same way as those processes operate today. The corollary to this was that the rates of the various ancient processes could be considered the same as those of the present day. Therefore, it should be possible to calculate the age of the Earth on the basis of the accumulated record of some process that has occurred at this determinable rate since the Creation. 

Many independent estimates of the age of the Earth have been proposed, each made using a different method of analysis. Some such estimates were based on assumptions concerning the rate at which dissolved salts or sediments are carried by rivers, supplied to the world's oceans, and allowed to accumulate over time. These chemical and physical arguments (or a combination of both) were all flawed to varying degrees because of an incomplete understanding of the processes involved. The notion that all of the salts dissolved in the oceans were the products of leaching from the land was first proposed by the English astronomer and mathematician Edmond Halley in 1691 and restated by the Irish geologist John Joly in 1899. It was assumed that the ocean was a closed system and that the salinity of the oceans was an ever-changing and ever-increasing condition. Based on these calculations, Joly proposed that the Earth had consolidated and that the oceans had been created between 80 and 90 million years ago. The subsequent recognition that the ocean is not closed and that a continual loss of salts occurs due to sedimentation in certain environments severely limited this novel approach.

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