It makes no sense at all if man appeared at the end of billions of years.
We will deal with carbon dating first and then with the other dating methods.
Carbon-14 is the parent isotope, its constant decay rate is about 5730 years.
Which means it takes that many years for it to decay to a stable daughter Nitrogen-14.
C) dating usually want to know about the radiometric dating methods that are claimed to give millions and billions of years—carbon dating can only give thousands of years.
The amount of cosmic rays reaching the Earth varies with the sun's activity, and with the Earth's passage through magnetic clouds as the solar system travels around the Milky Way galaxy.
The strength of the Earth's magnetic field affects the amount of cosmic rays entering the atmosphere.
The flood buried a huge amount of carbon, which became coal, oil, etc., lowering the total C ratio in plants/animals/the atmosphere before the flood had to be lower than what it is now.
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.