Up a tree dating
Academics believe that powerful solar storms caused bursts of radiation that showered down on Earth in 775 to 994 CE.
The two spikes, known as Miyake events, can be detected in the unusually high levels of radioactive carbon-14 in tree-rings that grew over that time period.
A measurement of the ratio, therefore, provides a way to estimate how much time has elapsed since the plant was alive.
Dendrochronology - tree-ring dating - and carbon-14 dating can be combined to date an event to a particular calendar year, the researchers said.
Dendrochronology results are presented either as PDF files or printed full colour written reports, which generally include a floor plan and photographic record of sample locations.