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In tree rings, Japanese scientists find 8th-century mystery

• http://phys.org, AFP

Analysis of two ancient trees found a surge in carbon-14 -- a that derives from -- which occurred just in AD 774 and AD 775, the team report in the journal Nature on Sunday.

Earth is battered by protons and other sub-atomic particles which are blasted across space by high-energy sources.

The particles collide with the stratosphere and react with nitrogen to create carbon-14, which is then absorbed into the biosphere.

A team led by Fusa Miyake of Nagoya University found that levels of carbon-14 in the two cedars were about 1.2 percent higher in 774 and 775 compared to other years.

This may not sound much, but in relation to background concentrations of carbon-14, the difference is huge.

One source of is the Sun, whose activity varies in phases called Schwabe cycles. Our star also throws the occasional tantrum, spouting bursts of energy called .

But Miyake's team say that the cosmic whack of 774-775 cannot be attributed to the Schwabe cycle of the time -- and it is far bigger than any known flare from the Sun.

The other possibility is a supernova, or a star that explodes at the end of its life in a welter of

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