The group theorizes that large errors in carbon dating result from fluctuations in the amount of carbon 14 in the air. Changes in the Earths magnetic field would change the deflection of cosmic-ray particles streaming toward the Earth from the Sun.

Why is there a limit to carbon dating?

Because C-14 dating uses the decay rate of Carbon 14 as its measure (more on this later), this gives upper and lower limits to the dating method. If the sample is too young, not enough decay has occurred. This means that the upper limit of C-14 dating is currently around 50,000 years ago.