Define absolute dating methods
We also see close agreement between dendrochronology and uncalibrated radiocarbon dates.
(I specify uncalibrated dates because as radiocarbon dating is calibrated against dendrochronology, the agreement of calibrated radiocarbon dates with dendrochronology is inevitable.) Now, each of these three methods relies on a different underlying physical process: radioactive decay, outwash from glaciers, and the growth of trees.
Throughout this process, they all go on showing exactly the same time.
Is it plausible that we have damaged their very different internal mechanisms in such a way that they are all running fast or slow but still in perfect synchrony?
Consider the following analogy: a clockmaker sells us an electric clock, a pendulum clock, and a spring-driven clock, and guarantees that they are shockproof.
Skeptical of the clockmaker's claim, we subject the clocks to shock: we shake them, drop them, hit them with hammers and shoot them out of a cannon.
If this does not completely prove that radiometric dating is correct, it does at least show that (barring a wildly improbable coincidence) there is at least a one-to-one relationship between the dates produced by radiometric methods and the true dates, and so it must be taken as an argument in favor of these methods.
It is possible to test radiocarbon dating by using it to put a date on historical artifacts of known date, and to show that it is usually very accurate.
Relative dating by definition does not produce actual dates, but it does allow us to put an order on the rocks, and so if absolute dating is to be trusted, it should agree with this order, telling us, for example, that Ordovician rocks are older than Triassic rocks; and it does.
Similar remarks may be made about the agreement between radiometric dating of rocks, sclerochronology, and dating by rhythmites.
Are we to believe that one single mechanism interfered with the decay of radioactive isotopes, the secretion of calcium carbonate by molluscs, and the action of the tide? But are we instead to believe that three separate mechanisms interfered with these processes in such a way as to leave all the dates concordant? The straightforward explanation for the concordance of the dates is that they are in fact correct.
Science, since it concerns just one universe with one set of laws, constitutes a seamless whole; we cannot unpick the single thread of absolute dating without the whole thing beginning to unravel.
Still, it has happened in the past that scientists have thought they'd got hold of a law of nature and then found out it was false.