A little under three million years ago, a massive star exploded in our galaxy about 300 light years away.
This supernova was so close to our planet that, depending on where it went off, our evolutionary ancestors might have seen it as a bright light in the sky.
As our solar system traveled through radioactive specks of stardust left over from the explosion, some of the dust broke through our atmosphere and rained down on our planet.
Now a recent find from deep within our still-vast ocean is helping us piece together details of a cosmic event that may have changed our planet millions of years ago.
Supernova junk in the ocean
In 2004, scientists found some of this supernova debris in oceanic crust from the Pacific Ocean. But until now, scientists had a tough time pinpointing exactly how long ago the supernova ejected its insides into space. That’s because the type of ocean crust they found the debris in grows extremely slowly — about 1 millimeter every million years.
In a new study published today in the Proceedings of the National Academy of Sciences (PNAS), scientists were able to figure out how long ago the star exploded and how much time our solar system spent traveling through its stellar guts. Not only was the length of time our solar system spent in the star’s remains surprising, it also coincides with an extinction event in Earth’s oceans, as well as a period of global cooling.
To get these results, the scientists used a different type of ocean sediment from the Pacific Ocean that grows at a rate of 10-20 meters every million years. They were searching for atoms of a radioactive isotope of iron called iron-60. Iron-60 is not produced on Earth, and can only be produced in these massive, exploding stars. In fact, this supernova debris is the first place in the history of our species that we’ve even seen it.
So what was it that preserved this 2.6 million-year-old radioactive isotope?