Throughout this process, they all go on showing exactly the same time.
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.
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.
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.
One argument in favor of the absolute dating methods presented in the preceding articles is that they should work in principle.
If they don't, then it's not just a question of geologists being wrong about geology, but of physicists being wrong about physics and chemists being wrong about chemistry; if the geologists are wrong, entire laws of nature will have to be rewritten.
This means that if we didn't have any other way of doing absolute dating, we would as a first approximation take the age of basalt on a spreading sea floor to be the distance from the rift divided by the rate of spreading.