Sometimes, when a massive star reaches the end of its life, its
core collapses in on itself, causing an epic explosion that can
light up the entire sky.
If this explosion happens close enough to our planet, it
can bombard us with high-energy radiation.
A new paper published in The Astrophysical Journal Letters
explores the effects
of two exploding stars, or supernovae, that
occured somewhere between 1.7 to 3.2 million and 6.5 to
8.7 million years ago.
The scientists used computer models to follow the radiation
down through the earth’s atmosphere to find out its effects,
as well as how much of it actually reached the
ground.
What they found was surprising.
Bathing in cosmic radiation
According to their models, at first, the explosions would have
caused blue light in the night sky “brilliant
enough to disrupt animals’ sleep patterns for a few weeks,”
said a University of Kansas press release.
Then, the explosion would have exposed our atmosphere and biology
to a “long-lasting gush of cosmic radiation.” For
hundreds to thousands of years, this radiation would have
increased by a factor of a few hundred.
This boost in radiation would have had “substantial effects on
the terrestrial atmosphere and biota,” the authors wrote in the
study, causing as much as a 20-fold increase in irradiation by
cosmic particles at Earth’s surface. This would just about triple
the radiation dose that creatures at ground level would be
exposed to.
Melott said this radiation would have packed doses equivalent to
one CT scan per year for every creature living on land
and in shallow parts of the ocean. This increase in
radiation would have been high enough to boost the mutation rate
and frequency of cancer, as well as possibly speed up evolution.
An era of lightning
As the radiation poured down on Earth, it would have ionized the
atmosphere, tearing apart atoms and molecules, so that electrons
were running around by themselves, kind of like gas inside
fluorescent tube.
This would conduct electricity easier, so scientists think that
there’s a good chance that the rate of lightning may have
increased a lot during the hundreds to thousands of years
that cosmic radiation was hitting Earth.
This could have caused more wildfires and could have potentially
changed the climate of the planet. In fact, the more recent
explosion coincides with a minor mass extinction around 2.59
million years ago.
“There was climate change around this time,”Adrian Melott,
professor of physics at the University of Kansas and co-author
the new paper, said in a press release. “Africa dried out,
and a lot of the forest turned into savannah. Around this time
and afterwards, we started having glaciations — ice ages
— over and over again, and it’s not clear why that started
to happen. It’s controversial, but maybe cosmic rays had
something to do with it.”
What comes next
The next step is for scientists to look at the geological record
around the time of the more recent explosion, and see if there
were more things like wildfires and mutations.
At the time of the study, the scientists believed the explosions
both happened about 300 light years away, but new results that
have come out since the paper was published that suggest that one
of the explosions might have happened at about half that
distance. So, the scientists also plan to redo their models with
that shorter distance. They expect that the effects will be even
bigger.
Even though these explosions might have transformed life on Earth
at that time, you shouldn’t be too worried about their effects on
us.
“This is not something for people to worry about for the
immediate future,” Melott said. “Events like this only come along
over long time periods of millions and millions of years.”
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