In the years 774 and 993 AD, the Earth was attacked from space.
Not by aliens, but by a natural event — and it was very, very powerful.
Whatever it was, it subtly altered the chemistry of our planet’s atmosphere, creating trace amounts of radioactive elements like chlorine-36, beryllium-10, and carbon-14. And those provide the clue to what the event was: Those isotopes are created when high-energy protons slam into our air. That means the source must have been from space.
These must have been huge waves of subatomic particles that slammed into us on those dates. Spikes in the abundances of those elements were found all over the world, including ice cores from the Arctic and Antarctic, Chinese corals, and more. Generating that many particles isn’t easy, and only extremely violent events can do it.
Several possible sources have been considered. One candidate is that the Earth got caught in the beam from a gamma-ray burst, the mind-crushingly powerful demise of a very high mass star. I wrote about this being the possible cause of the 774 event in an earlier article. However, GRB impacts don’t usually create 10Be due to the detailed physics of the blast, so that makes a GRB as the source shaky. Plus, they’re very rare events, so having two happen in as many centuries is extremely unlikely (I didn’t know about the 993 AD event when I wrote that article, or else I would’ve been a lot more likely to wonder about other sources).
New research studying the amounts of these radioactive materials in ice cores points to a different culprit, one I wouldn’t have thought possible: the Sun.