What is being measured in radiometric dating

Since 1955 the estimate for the age of the Earth has been based on the assumption that certain meteorite lead isotope ratios are equivalent to the primordial lead isotope ratios on Earth.

In 1972 this assumption was shown to be highly questionable.

The example used here contrasts sharply with the way conventional scientific dating methods are characterized by some critics (for example, refer to discussion in "Common Creationist Criticisms of Mainstream Dating Methods" in the Age of the Earth FAQ and Isochron Dating FAQ).

It is these highly consistent and reliable samples, rather than the tricky ones, that have to be falsified for "young Earth" theories to have any scientific plausibility, not to mention the need to falsify huge amounts of evidence from other techniques.

by Tas Walker A geologist works out the relative age of a rock by carefully studying where the rock is found in the field.

The field relationships, as they are called, are of primary importance and all radiometric dates are evaluated against them.

He would have answered that the Earth was ancient, that there had not been a Noachian flood, and that the species of life had not been fixed over the history of Earth.

In short, Genesis was an allegory and not literal history.