Fourteen thousand years ago, a star called Vela died. Its core collapsed first and then, in a violent burst, propelled the shattered star’s body out into space. Vela’s death bled into the interstellar medium, blasting cosmic radiation out in every direction.
For 800 years, the guts of this star traveled from its location in the Milky Way galaxy toward Earth. It took several years for the cosmic rays to permeate our atmosphere and settle to the ground, where they were absorbed into trees, ocean coral, and lakes around the planet.
Hundreds of years after that, in Tasmania, a dead tree was discovered, turned by time into a log and buried under sediment. Scientists studied the radioisotopes of the tree’s rings and found a surge of radiation 14,000 years old.