Processes affecting radiometric dating techniques
If extra lead were to have been absorbed in the rock after the original formation, the new lead would have caused the calculated ages of the rock to diverge unless it contained the right proportion of lead-206 to lead-207.If the ratio of lead-206 to lead-207 in the newly introduced rock were greater than the ratio of lead-206 to lead-207 found in an uncontaminated system, the method of dating based on the decay of uranium-238 to lead-206 would give a relatively higher value than the method of dating based on the decay of uranium-235 to lead-207.
Argon is an inert gas, so that it does not occur in chemical compounds in original rocks.Given this value of Dit is then possible to use either decay process to calculate the age of the rock.If the results agree, they are said to be concordant, and geologists are usually confident that concordant ages are the true ages of the rocks under consideration.However, I hope that it will help to quell anxieties when I point out that a large number of independent methods have been applied to a vast array of different rocks.
The result of this enormous array of tests is a consensus. The process rate must always have been the same" (Morris 1974a, 138).The chief defect of the potassiumargon method is that, under the action of heat or compression, argon can escape from rocks, so that the estimated age is less than the true value.