Geological dating techniques of earth
Charles Darwin reinforced this idea by pointing to the time that must have been required for the EVOLUTION of advanced life from primitive forms.
On the other hand, the great physicist Lord Kelvin vehemently objected and suggested that the Earth might only be a few tens of millions of years old, based on his calculations of its cooling history.
Using the uranium-lead technique they dated zircon crystals from the gneiss (located southeast of Great Bear Lake in the NWT) and showed that it was formed almost 4 billion years ago.
Therefore it is clear that the Earth is over 4 billion years old.
Samuel Bowring, now of the Massachussetts Institute of Technology, and his coworkers Ian Williams and William Compston of the Australian National University at Canberra have shown that a small area of metamorphic rock in northern Canada, known as the Acasta gneiss, is the oldest known intact solid piece of the Earth's crust.It has even been possible to work out a time scale of the reversals of the Earth's magnetic field.This "radiometric" approach has superseded all other techniques for determining absolute ages. Their nuclei tend to emit particles spontaneously - ie, they are radioactive.Since 1950, radiometric methods have been developed to a very sophisticated level in several countries, including Canada.It has been demonstrated that when rocks which have led an undisturbed history are analysed, all methods reveal the same age.