When high-energy radiation strikes the upper atmosphere it turns nitrogen atoms into radioactive carbon-14, or radiocarbon. The radiocarbon then filters through the air and the oceans, into sediments and bogs, into you and me, into animals and plants—including hardwoods with their yearly tree rings.

To archaeologists, radiocarbon is a godsend. After it is created, carbon-14 slowly and steadily decays back into nitrogen—which means it can be used as a clock to measure the age of organic samples, in what is called radiocarbon dating.

To astronomers, this is equally valuable. Tree rings give a year-by-year record of high-energy particles called “cosmic rays” going back millennia.

But tree rings also record events we cannot presently explain. In 2012, Japanese physicist Fusa Miyake discovered a spike in the radiocarbon content of tree rings from 774 AD. It was so big that several ordinary years’ worth of cosmic rays must have arrived all at once.

As more teams have joined the search, tree ring evidence has been uncovered of further “Miyake events”: from 993 AD and 663 BC, and prehistoric events in 5259 BC, 5410 BC, and 7176 BC…

If an event like this occurred today, it would devastate power grids, telecommunications and satellites. If these occur randomly, around once every thousand years, that is a 1% chance per decade—a serious risk.

“Doomed. We’re all doomed, I say. Doomed.”