Supernovas
are awesome things that only happen very far from earth and don’t affect us,
aren’t they? Well, it turns out they do, says Adrian L. Melott in this week’s
Nature. But how have supernovas changed life? And will it happen again?
The universe comes with built-in firework
Supernovas
happen when stars that are eight times as big as our sun come to the end of
their lives. If these stars are going to die, their cores get so heavy that
they implode. This implosion creates a huge shockwave, which rips the outer
layers of the dying star apart. This
layers then start float around the imploded star, and they form a nebula, like
you can often see in beautiful pictures taken by Hubble. The implosion also
emits all kinds of radiation of different wavelengths, like visible light,
that’s the reason we could be able to see a supernova, if one went off, or
radio waves, but also dangerous gamma- and X-rays. The supernova also sends all
kinds of radioactive materials into space.
CSI: Supernova
CSI: Supernova
Fortunately,
supernovas have never happened so close to earth that we felt any of the
consequences of these gamma- and X-rays, or have we? Anton Walnner and his team
have found extremely large quantities of a radioactive material in the earth’s
crust. Sometimes even 40 times as much as normal. After analysing the
radioactive material, they concluded that they must have come from supernovas. Multiple
supernovas in fact, which occurred in two spurts; one spurt around two and a
half billion years ago and another around seven and a half billion years ago. These
supernovas didn’t cause any mass-extinctions, since the last one was 65 billion
years ago, when the dinosaurs died. But the supernovas might have had another
consequence.
Freezing firework
The last
spurt of supernovas was around two and a half billion years ago, and around
that time, a new ice age started. Although scientists haven’t been able to
prove a connection between supernovas and ice ages yet. It is a fact, however,
that the evolution of humans was hugely influenced by this ice age. So we might
thank our existence to supernovas.
We’re all gonna die!
The bad
news is, however, that those same supernovas could wipe us out again just as
easily. A supernova that is twenty-six lightyears away from earth (that’s like
nine million years if you wanted to go there by car), could already kill more
than half of all life on earth. Fortunately, supernovas that are this close to
earth don’t happen very often and it is very unlikely that we will be killed by
a supernova any time soon. Oh wait, what’s that bright light in the sky…
Sources:
http://sci-hub.bz/10.1038/532040a
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