Referenced here is a peer reviewed article about the Maunder Minimum where it is noted that solar activity affects 14C production in the atmosphere. When cosmic rays strike earths atmosphere, 14N gets converted to 14C, which is unstable. The 14C atoms which join with O2 to form CO2 however maintain the 14C from reverting back into 14N. Being locked away in a molecule, it slowly decays over time to 12C, a more stable form of carbon.
The article mentions how when solar activity is at maximum, fewer cosmic rays can reach the earth to create C14. When it is at minimum, more cosmic rays can reach earth that more 14C is produced (See Citation Below). This makes perfect sense considering that cosmic rays are charged subatomic particles. More intense activity would mean a more vigorous solar wind resulting in more particles from the sun to be a barrier to cosmic rays reaching the earth. Consequently, less solar activity allows for more cosmic rays reaching the earth.
Another thing similar in concept to the solar cycles affecting cosmic rays interacting with earths atmosphere is earths magnetic field. A stronger magnetic field would deflect more cosmic rays than a weaker one. Earths magnetic field, with a half-life of 1400 years is set to be depleted in less than 2,000 years. Therefore, it would have hindered the production of 14C in the past compared to the present.
What does this all mean? Simply that the production of 14C in earths atmosphere is not a constant and production in the past was likely less than what is observed today. We cannot assume that creatures, even a century ago, died with a 14C to 12C ratio similar to what is observed today and interpolate back in time to determine an assumed age. While it is often said that Carbon dating is good for objects no more than 50,000 - 70,000 years in age, it is in fact good only for objects that are 0 years of age.
Reference:
