Researchers consider whether supernovae killed off large ocean animals at dawn of Pleistocene
Mass extinctions on Earth are like a strange cycle.
Approximately 2.6 million years ago, a strangely bright light reached the prehistoric sky and remained there for weeks or months.
It was a supernova located some 150 light years from Earth.
In a few hundred years, long after the strange light in the sky had diminished, a tsunami of cosmic energy from the same star explosion reached our planet and crashed into the atmosphere, causing dramatic climate change and unleashing a massive world-wide extinction.
The effects of such a supernova and what happened on Earth are detailed in a paper recently published in Astrobiology.
“I’ve been doing research like this for about 15 years, and always in the past it’s been based on what we know generally about the universe — that these supernovae should have affected Earth at some time or another,” explained lead author Adrian Melott, professor emeritus of physics & astronomy at the University of Kansas.
“This time, it’s different. We have evidence of nearby events at a specific time. We know about how far away they were, so we can actually compute how that would have affected the Earth and compare it to what we know about what happened at that time — it’s much more specific.”
According to scientists, the recent study reveals ancient seabed deposits of iron-60 isotopes that offer unequivocal evidence of the timing and distance of supernovae.
“As far back as the mid-1990s, people said, ‘Hey, look for iron-60. It’s a telltale because there’s no other way for it to get to Earth but from a supernova.’ Because iron-60 is radioactive, if it was formed with the Earth it would be long gone by now. So, it had to have been rained down on us.”
“There’s some debate about whether there was only one supernova really nearby or a whole chain of them. I kind of favor a combo of the two — a big chain with one that was unusually powerful and close. If you look at iron-60 residue, there’s a huge spike 2.6 million years ago, but there’s excess scattered clear back 10 million years.”
But there’s more.
According to the co-authors of the study, Marinho of Universidade Federal de São Carlos in Brazil and Laura Paulucci of Universidade Federal do ABC, evidence for a series of supernovae can be discovered in the very architecture of the local universe.
“We have the Local Bubble in the interstellar medium,” Melott explained.
“We’re right on its edge. It’s a giant region about 300 light years long. It’s basically very hot, very low-density gas — nearly all the gas clouds have been swept out of it. The best way to manufacture a bubble like that is a whole bunch of supernovae blows it bigger and bigger, and that seems to fit well with the idea of a chain.”
“When we do calculations, they’re based on the idea that one supernova that goes off, and its energy sweeps by Earth, and it’s over. But with the Local Bubble, the cosmic rays kind of bounce off the sides, and the cosmic-ray bath would last 10,000 to 100,000 years. This way, you could imagine a whole series of these things feeding more and more cosmic rays into the Local Bubble and giving us cosmic rays for millions of years.”