So, we have a “clock” which starts ticking the moment something dies.
Obviously, this works only for things which were once living.
For example, potassium-40 decays to argon-40; uranium-238 decays to lead-206 via other elements like radium; uranium-235 decays to lead-207; rubidium-87 decays to strontium-87; etc.
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.
This is the “half-life.” So, in two half-lives, or 11,460 years, only one-quarter of that in living organisms at present, then it has a theoretical age of 11,460 years.
Anything over about 50,000 years old, should theoretically have no detectable C.
Unless this effect (which is additional to the magnetic field issue just discussed) were corrected for, carbon dating of fossils formed in the flood would give ages much older than the true ages.