In this period a number of comprehensive cosmogonies were proposed.These were long on armchair speculation and short on substantive supporting evidence.

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If, in the year AD 1600, you had asked an educated European how old the planet Earth was and to recount its history he would have said that it was about 6000 years old and that its ancient history was given by the biblical account in Genesis.

If you asked the same question of an educated European in AD 1900 you would have received a quite different answer.

When asked for your age, it's likely you won't slip (with the exception of a recent birthday mistake).

But for the sprawling sphere we call home, age is a much trickier matter.

Students not only want to know how old a fossil is, but they want to know how that age was determined.

Some very straightforward principles are used to determine the age of fossils.Meanwhile, Arthur Holmes (1890-1964) was finishing up a geology degree at the Imperial College of Science in London where he developed the technique of dating rocks using the uranium-lead method.By applying the technique to his oldest rock, Holmes proposed that the Earth was at least 1.6 billion years old.Our planet was pegged at a youthful few thousand years old by Bible readers (by counting all the "begats" since Adam) as late as the end of the 19th century, with physicist Lord Kelvin providing another nascent estimate of 100 million years.Kelvin defended this calculation throughout his life, even disputing Darwin's explanations of evolution as impossible in that time period.These cosmogonies were part of the new emphasis of science in seeking rational explanations of the features of the world. This period was marked by a great deal of field geology rather than grand cosmogonies.