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March 26, 2013

More than 12 centuries ago, a big burst of cosmic energy zapped Earth. It caused a spike in radioactive carbon-14 in the atmosphere, some of which was absorbed by trees. And today, those trees have started a fast-moving debate about the source of the energy.

The debate began when Japanese researchers measured high levels of carbon-14 in the rings of Japanese cedar trees from the years 774 and 775. The levels were consistent with those found in trees in Europe and North America at about the same time. The levels suggested that Earth was bombarded by high levels of high-energy gamma rays. They triggered a chain reaction that resulted in higher-than-normal levels of the radioactive carbon.

The Japanese researchers suggested the outburst came from the Sun or from a relatively nearby exploding star, known as a supernova. A few months later, another team zeroed in on the Sun. The team said it would be possible for the Sun to produce an unusually powerful explosion known as a solar flare, along with a massive “puff” of charged particles from its surface.

Then late last year, another team suggested yet another possibility: a gamma-ray burst. The team found no evidence of a supernova at the right distance to cause such an event, and said there was little to suggest the Sun could produce the right kind of outburst, either. That left a type of gamma-ray burst caused by a collision between two small but heavy objects. We’ll have more about that tomorrow.


Script by Damond Benningfield, Copyright 2013

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