Cosmic Cedar

Tree rings are frozen environmental records. Unlike many other historical data that are averaged over decades or even centuries, tree rings grow in distinct individual annual segments. These segments are indicative of the environment the tree experienced during a specific year. In general, more favorable conditions of moisture and length of the growing season result in wider rings. Tree rings of multiple trees growing nearby are closely correlated, and their ages can be cross-correlated with carbon-14 dating techniques; tree rings can be tied to specific years.

It has recently been discovered that rings from cedar trees grown on Japan’s Yakushima island show an unusually high content of the carbon-14 isotope in rings formed in the late 8^th century. Carbon-14 in rings from a specific year (775 AD) jumped 12% from the prior year, which is 20 times the normal variability of C-14 due to solar modulation. High C-14 levels have been found in contemporaneous samples of European and North American forests. The high C-14 levels are believed to have been caused by an extremely intense burst of radiation, still of unknown origin.

Studies of arboreal growth patterns are important for the determination of climate history as well as of the impact of cosmic events on life on Earth.

http://www.nature.com/nature/journal/v486/n7402/full/nature11123.html