Looking at the history of dating the Earth is instructive because methods were used before the discovery of radioactivity and its application in radio-dating.
James Hutton in his "Theory of the Earth", published in 1795, proposed that the land was slowly and gradually eroded into the seas and the sediments hardened by heat and were raised again to form new land. He saw no evidence of the Earth's beginning only a slow recycling of the land. He was the first so-called uniformitarian and though he did not provide an age for the Earth, thought it to be unimaginably old
Later Charles Lyell published his "Principles of Geology" in 1830, basing his ideas on Huttons uniformitarianism. Lyell thought the geological features of the earth could only be explained by slow perpetual processes of erosion, sedimentation reforming etc., operating at the same rate they do today. That is:-
- Studies of strata suggested that they were laid down by natural processes in which the sea and land had changed places several times.
- Studies of earthquakes and volcanoes showed that the surface crust is subject to massive natural transformation.
- Observation of rain, wind, water erosion, and sea erosion in action showed that they were forces capable of reducing mountains and creating valleys.
William Smith (17691839) produced geological maps of England and Wales and was the first person to use fossils to assign relative dates to the strata. His studies led him to believe the Earth was much older than 6,000 years
During this period there was a considerable debate between various parties, but the efforts of the biblical geologists failed and by 1830 this was a dead issue in science. Of course today, although the uniformitarian principle is used in geology, it is recognised that the Earth has experienced several catastrophic events in its lifetime.
The first person to actually calculate an age for the Earth seems to have been William Thomson (Lord Kelvin, 18241907). Assuming the Earth was originally a molten object and using measured rates of heat loss, he calculated an age of between 20 million and 400 million years. However, he did not take into consideration convection currents within the Earth, nor was he aware of the heat produced inside the Earth by radioactivity, both of which would have led to a severe underestimation.
In 1899 and 1900, John Joly of the University of Dublin calculated the rate at which the oceans should have accumulated salt from erosion processes, and determined that the oceans were about 80 to 100 million years old.
Following the discovery of radio-isotopes and the way they disintegrated into different elements, attempts were made to use this method to date the Earth. Arthur Holmes, a pioneer in this emerging technology, published "The Age of the Earth, an Introduction to Geological Ideas" in 1927 in which he presented a range of 1.6 to 3.0 billion years. Since then numerous measurements have been made using radiometric different techniques.
Age of the Earth - Wikipedia, the free encyclopedia
http://www.geosociety.org/gsatoday/archive/17/1/pdf/i1052-5173-17-1-4.pdf
G. Brent Dalrymple is considered an expert on this subject and has written a book entitled "The Age of the Earth"
Amazon.com: The Age of the Earth (9780804723312): G. Dalrymple: Books
It's interesting to read his comments:-
Evidence for an old Earth does not tell us whether the rest of the universe is older, but it does tell us it cannot be younger.