Supernovae explosions’ radioactive fallout once covered Earth

7 Apr 2016

Exploding supernova image via NASA

Two new studies have revealed that during the time of our earliest ancestors millions of years ago, the explosions of nearby supernovae spewed radioactive fallout across the Earth.

The discovery of this ancient radioactive fallout was made by researchers taking part in a study analysing the cores extracted during deep-sea drilling from the depths of the Atlantic, Pacific and Indian oceans.

According to GeekWire, one of the studies, published in Nature, that came to this conclusion had obtained samples dated from between 1.5m and 3.2m years ago, as well as between 6.5m and 8.7m years ago.

Once the samples were analysed, the team from the Australian National University, led by Anton Wallner, was able to see that within the ancient samples were deposits of radioactive iron-60 that could have only come from cataclysmic cosmic events, like the explosions of supernovae that happened within 325 light years of Earth.

The second study, also published in Nature, conducted by the Berlin Institute of Technology, looked at the iron-60 samples more closely to determine a timeframe for when these explosions would have occurred and what size the stars were that could have caused such a wide-scale fallout.

Could be seen from Earth during the daytime

Going by the team’s estimates, it has been calculated that two explosions led to the spread of the fallout, the first of which occurred 2.3m years ago of an exploding star approximately 9.2 times the size of our own sun.

The second explosion likely occurred 1.5m years ago by a similarly enormous star, approximately 8.8 times the size of the sun.

For our earliest ancestors, the events would have caused quite a stargazing event, with the resulting explosions lighting up the night sky to the same degree as the moon does, and would even have been visible during the day.

Aside from the fallout caused by the explosions, the research team is now investigating what, if any, effects were experienced by the planet.

“Our local research group is working on figuring out what the effects were likely to have been,” said astrophysicist Adrian Mellot, who spoke as someone not involved with either study.

“We really don’t know. The events weren’t close enough to cause a big mass extinction or severe effects, but not so far away that we can ignore them either. We’re trying to decide if we should expect to have seen any effects on the ground on the Earth.”

Colm Gorey was a senior journalist with Silicon Republic