Overall, the energy of the Earth's magnetic field has been decreasing, so more C is being produced now than in the past.
We will deal with carbon dating first and then with the other dating methods.
Carbon has unique properties that are essential for life on Earth.
To derive ages from such measurements, unprovable assumptions have to be made such as: There is plenty of evidence that the radioisotope dating systems are not the infallible techniques many think, and that they are not measuring millions of years. For example, deeper rocks often tend to give older “ages.” Creationists agree that the deeper rocks are generally older, but not by millions of years.
Geologist John Woodmorappe, in his devastating critique of radioactive dating, points out that there are other large-scale trends in the rocks that have nothing to do with radioactive decay.
It cannot be used to date volcanic rocks, for example.
The rate of decay of N in 5,730 years (plus or minus 40 years).The strength of the Earth's magnetic field affects the amount of cosmic rays entering the atmosphere.A stronger magnetic field deflects more cosmic rays away from the Earth.This also has to be corrected for. Second, the ratio of C in the atmosphere at that time to be estimated, and so partial calibration of the “clock” is possible.Accordingly, carbon dating carefully applied to items from historical times can be useful.Familiar to us as the black substance in charred wood, as diamonds, and the graphite in “lead” pencils, carbon comes in several forms, or isotopes.