How old is the Earth? Scientists and theologians, geologists and physicists have been haggling over this question for hundreds, if not thousands, of years.
And while there is general consensus among the scientific community today that Earth is about 4,500 million years old, this accord was not always present.
A lecturer in geology at Trinity College Dublin has detailed efforts over the centuries to measure the age of the Earth. The Chronologers' Quest details the battles and the skirmishes, the theories and counter theories that litter the landscape of this subject.
The book is by geologist and curator of the Geological Museum at Trinity, Dr Patrick Wyse Jackson. In tremendously readable and non-scientific language, he talks about the contributions made to establishing the Earth's age.
The Irish were very prominent in this effort, says Wyse Jackson. "There were quite a few Irish people, starting off with Ussher."
Archbishop of Armagh James Ussher produced one of the "definitive" calculations of the age of the Earth, relying in the main on the Old Testament, but also including studies of Egyptian and Hebrew texts. He concluded in 1650 that the world began the evening before October 23, 4004 BC, making it a very young Earth indeed.
Ussher wasn't the only one relying on the Bible, says Wyse Jackson. There were no fewer than 250 such calculations done but Ussher's claimed pole position. "Ussher is important because his calculation got published in 1701 in the King James Bible."
Other Irish contributions were made by Rev Samuel Haughton (1821-1897), who calculated the age of the Earth on the basis of its temperature and how quickly it must have cooled from its original molten state. His best estimate was 2,298 million years old.
Belfast-born William Thompson, Lord Kelvin, also relied on global cooling principles to determine age, but his best estimate was about 98 million years, with a range from 20 million to 400 million years old.
"The person who did the most about determining the age of the Earth was (John) Joly," says Wyse Jackson. He used yet another method, measurements of the amount of sodium in the oceans. It involved dividing the calculated tonnage of sodium present in the oceans by the assumed tonnage entering the oceans from the Earth in a year. His figures suggested the Earth was at least 90 million and not more than 100 million years old.
Quite novel methods were used to measure the age of the Earth, Wyse Jackson says. Welshman Edward Lhwyd (1660-1709) tried counting the number of large boulders that had fallen from a mountain top into a valley, assuming a given number of years between such incidents. Not surprisingly, he didn't actually deliver a final figure.
Georges-Louis Leclerc, Comte de Buffon (1707-1788) did extensive experimentation on the time it took for small metal spheres heated to incandescence to cool. It was a matter of calculating up to match the volume of the Earth, his figure reaching 74,047 years.
The author's final chapter describes the analysis of lead recovered from meteorites which were assumed to date from the formation of the earth. Work by Clair Cameron Patterson (1922-1995) dated the meteorites - and so the earth - to 4,500 million years old, a figure that has stuck with us since his research in the 1950s.
• The Chronologers' Quest, The Search for the Age of the Earth, is published by Cambridge University Press
