Dating on earth summary
Considering that the half-life of potassium-40 (40K) is fairly long (1,250 million years, Mc Dougall and Harrison, 1999, p.
9), the K-Ar method cannot be used to date samples that are much younger than 6,000 years old (Dalrymple, 1991, p. A few thousand years are not enough time for 40Ar to accumulate in a sample at high enough concentrations to be detected and quantified.
He concluded that Earth was born 20 to 400 million years ago.
Today’s scientists believe that answer is incorrect, but Kelvin’s calculations were in being based on logical thinking and mathematical calculation.
Therefore, it's not surprising that some of Austin's dates, such as the result for the amphiboles, etc., 'fraction,' have large /- uncertainties.
'One critic said that Dr Austin should not have sent young samples to the dating laboratory because it potentially puts "large error-bars on the data." By this reasoning, the method could not be used on any rocks, since, if we did not see the rocks form, how would we know whether they are young?