In addition to permitting more accurate dating within archaeological sites than previous methods, it allows comparison of dates of events across great distances. Korff , then employed at the Franklin Institute in Philadelphia , that the interaction of thermal neutrons with 14 N in the upper atmosphere would create 14 C. This effect is accounted for during calibration by using a different marine calibration curve; without this curve, modern marine life would appear to be years old when radiocarbon dated. The calculations given above produce dates in radiocarbon years: The northern and southern hemispheres have atmospheric circulation systems that are sufficiently independent of each other that there is a noticeable time lag in mixing between the two.