Consistent with this are the results of Stephen Moorbath and his colleagues at Oxford, who have shown that rocks near Godthaab in southwest Greenland either formed or were in existence approximately 3.8 billion years ago.These results have been confirmed and agreement has been found among the rubidium-strontium, uranium-lead and samarium-neodymium methods.

The other key dating techniques involve uranium-235 transforming to lead-207 at a rate of one-half every 713 million years, uranium-238 becoming lead-206 at one-half every 4.5 billion years, potassium changing to argon (and calcium) at one-half every 1.3 billion years and samarium-147 becoming neodymium-143 at one-half every 106 billion years.

These radioactive processes present a set of natural clocks which reveal when the rock was formed, or when it was last heated severely.

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.

They were found, however, in much younger sediment and it is not known where these zircons originated.

The second approach, which is more indirect but gives an answer currently believed correct, involves a comparison of the Earth with meteorites.

The remaining number of radioactive atoms is halved every half-life.

Radioactive elements of use in geological dating have relatively long half-lives.

This uniformity demonstrates that the principle is reliable.