Tree rings can tell you a lot: The Japanese have discovered that, in the late eighth century, the earth was hit by a mysterious blast of cosmic rays (NOTE: Subscribers can still listen to this show). They discovered this by looking at cedar trees.

An analysis of two ancient trees found a surge in carbon-14, an isotope that arrives from space, which was deposited in cedar tree rings only in 774 and 775 AD. What happened?
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If a star were to explode near the Earth, we would be hit with millions of deadly particles and cosmic rays, causing mass extinctions due to the high radiation of cosmic rays, which strips away our planet’s protective ozone layer. Astronomers think this happens about every 60 million years (NOTE: Subscribers can still listen to this show).
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