The group theorizes that large errors in carbon dating result from fluctuations in the amount of carbon 14 in the air. Carbon dating is unreliable for objects older than about 30,000 years, but uranium-thorium dating may be possible for objects up to half a million years old, Dr. Zindler said.

Is carbon dating more accurate than stratigraphy?

Radiocarbon dating only works with artifacts that were never alive. Carbon dating is more accurate than stratigraphy.