TOPEKA, Kan. (AP) -- Two Kansas professors are making the case that a major solar burst may have happened more than 1,200 years ago.

Brian Thomas of Washburn University and Adrian Melott of the University of Kansas became interested after reading that tree samples from the years 774 and 775 showed a spike in the amount of carbon-14 in the atmosphere. The Japanese scientists who made the discovery ruled out a major solar event based on their calculations.

Thomas and Melott noticed that those calculations assumed the solar event would emit energy evenly. But Thomas is an associate professor of physics and astronomy, and he says that's not how the complicated energy bursts at the sun's surface actually work.

Thomas and Melott's response appeared in the online edition of the journal Nature.