Many people know an asteroid wiped out dinosaurs 66 million years ago. But Earth has faced at least five mass extinctions, not all from space rocks. Scientists now believe two extinctions—one 372 million years ago and another 445 million years ago—may have started with dying stars light-years away.
Supernovas and Ice Ages
A new study suggests these ancient disasters were triggered by nearby supernovas. Researchers analysed a vast number of stars in the Milky Way. Their findings indicate that massive stellar explosions may have caused ice ages on Earth.
"If a massive star exploded close to Earth, life would suffer," said Nick Wright, an astrophysicist at Keele University in the UK. "This study suggests it has happened before."
The Ordovician extinction wiped out 60% of sea creatures when life was mostly in the ocean. The late Devonian extinction removed 70% of species, reshaping marine ecosystems. Scientists have long suspected that ozone layer damage played a role in these events. Now, they think supernovas may have been the trigger.
Deadly and Creative Cosmic Events
Supernovas are powerful explosions marking the death of massive stars. They spread elements like carbon, calcium, and iron across space. This process fuels new stars and planets, inspiring astronomer Carl Sagan’s phrase: "We are made of star stuff."
However, supernovas can also be deadly. If one explodes within 65 light-years of Earth, it could strip away the ozone layer. This would expose the planet to harmful radiation and acid rain.
Using data from sky surveys, including the European Space Agency’s Gaia mission, researchers examined nearly 25,000 massive stars within 3,260 light-years of the sun. They found that supernovas close enough to affect Earth occur roughly every 400 million years.
For now, Earth is safe. The nearest stars expected to explode, like Betelgeuse and Antares, are over 500 light-years away. While past extinctions may have been shaped by these cosmic blasts, another event is unlikely anytime soon.
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