Supernovae May Have Sparked Ancient Cooling on Earth

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The Crab Nebula, a remnant of a recent supernova, was 10 times too far away to sprinkle the Earth with radioactive iron, but millions of years ago there were much closer events. Reinhold Wittich/Shutterstock

Researchers have found evidence for at least two, and probably several more, supernova explosions near Earth over the last 8 million years. Some of these may have contributed to the cooling of the planet, triggering recent ice ages.

Most of the universe's heavy elements are the result of supernova explosions, which fuse atomic nuclei and disperse them across surrounding regions. The products include radioactive isotopes that could not originate from other sources, as any that were part of the Earth's formation have long since decayed.