Supernova blasted Earth 2.5 million years ago (and may have triggered an ice age)

Astronomers were worried last year when a supergiant star visible to the naked eye from Earth started dimming amid concerns it might explode.

Such an explosion could cause serious harm to life on Earth if it was close enough.

But while Betelgeuse has returned to normal, researchers have found evidence that Earth was blasted by another exploding star 2.5 million years ago.

It may even have triggered an ice age, the researchers believe.

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When stars more than ten times bigger than our sun die, they explode in a supernova, a vast explosion.

The explosions lead to the formation of heavy elements found on Earth, including iron and manganese.

Researchers at the Technical University of Munich (TUM) analysed layers of a manganese crust around two and a half million years old.

The researchers found both iron-60 and manganese-53

Dr. Gunther Korschinek said, "The increased concentrations of manganese-53 can be taken as the "smoking gun" - the ultimate proof that this supernova really did take place.”

The researchers say that while the supernova was too far away to damage life on Earth, it caused a boost in cosmic rays over thousands of years.

In turn, this may have triggered an ice age.

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Co-author Dr Thomas Faestermann says, “This can lead to increased cloud formation,"

"Perhaps there is a link to the Pleistocene epoch, the period of the Ice Ages, which began 2.6 million years ago."

Typically, manganese occurs on Earth as manganese-55. Manganese-53, on the other hand, usually stems from cosmic dust, like that found in the asteroid belt of our solar system.

New sediment layers that accumulate year for year on the sea floor preserve the distribution of the elements in manganese crusts and sediment samples.

Using accelerator mass spectrometry, the team of scientists has now detected both iron-60 and increased levels of manganese-53 in layers that were deposited about two and a half million years ago.

"This is investigative ultra-trace analysis," says Korschinek. "We are talking about merely a few atoms here. But accelerator mass spectrometry is so sensitive that it even allows us to calculate from our measurements that the star that exploded must have had around 11 to 25 times the size of the sun."

WATCH: Supernova caught in time-lapse video