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Life was trying, but it wasn’t working. As the Late Devonian period lengthened, more and more living things became extinct, culminating in one of the largest mass extinction events our planet has ever seen, approximately 359 million years ago. ‘years.
The culprit responsible for so many deaths may not be local, scientists are now saying. In fact, it might not even have come from our solar system.
On the contrary, a new study led by astrophysicist Brian Fields of the University of Illinois at Urbana-Champaign suggests that this great extinguisher of life on Earth could have been a distant and completely alien phenomenon – a dying, exploding star. far across the galaxy, many light years away. away from our own remote planet.
It is sometimes thought that massive deaths like the Late Devonian extinction are triggered by exclusively terrestrial causes: a devastating volcanic eruption, for example, that suffocates the planet in death.
Or, it could be a deadly visitor from out of town – an asteroid collision, like the one that killed the dinosaurs. The death of space, however, could ultimately come from places much further away.
“The main message of our study is that life on Earth does not exist in isolation,” says Fields.
“We are citizens of a larger cosmos, and the cosmos intervenes in our lives – often imperceptibly, but sometimes fiercely.”
In their new work, Fields and his team are exploring the possibility that the dramatic drop in ozone levels coinciding with the Late Devonian extinction was not the result of volcanism or an episode of global warming.
Instead, they suggest that it is possible that the biodiversity crisis exposed in the geological records could have been caused by astrophysical sources, speculating that the effects of radiation from one supernova (or more) to around 65 Light-years from Earth may have been what depleted our planet’s ozone. such a disastrous effect.
This may be the first time such an explanation has been put forward for the Late Devonian extinction, but scientists have long considered the potentially lethal repercussions of near-Earth supernovas in this type of context.
Speculation that supernovas could trigger mass extinctions dates back to the 1950s. More recently, researchers have debated the estimated “destruction distance” of these explosive events (with estimates ranging between 25 and 50 million years ago). light).
In their new estimates, however, Fields and his co-authors suggest that exploding stars even further away could have detrimental effects on life on Earth, through a possible combination of instant and long-term effects.
“Supernovae (SNe) are rapid sources of ionizing photons: extreme UV, X-rays and gamma rays,” the researchers explain in their article.
“On longer time scales, the explosion collides with the surrounding gas, forming a shock that causes the particles to accelerate. In this way, SNe produces cosmic rays, that is, atomic nuclei accelerated to high energies. These charged particles are magnetically confined within the rest of SN, and are expected to bathe the Earth for ~ 100 ky [approximately 100,000 years]. “
These cosmic rays, the researchers say, could be powerful enough to deplete the ozone layer and cause long-lasting damage to life forms inside the Earth’s biosphere – which roughly matches the evidence from the loss of diversity and deformations in ancient plant spores found in deep rock of the Devonian – Carboniferous border, laid about 359 million years ago.
Of course, this is only a guess for now. At the present time, we have no evidence that can confirm that a distant supernova (or supernovae) was the cause of the Late Devonian extinction. But we may be able to find something as good as proof.
In recent years, scientists examining the prospect of near-Earth supernovas as the basis for mass extinctions have looked for traces of ancient radioactive isotopes that could only have been deposited on Earth by exploding stars.
One isotope in particular, iron 60, has been the subject of much research and has been found in many places on Earth.
In the context of the Late Devonian extinction, however, other isotopes would be strongly indicative of the supernova extinction hypothesis put forward by Fields and his team: plutonium-244 and samarium-146.
“None of these isotopes occur naturally on Earth today, and the only way to get there is through cosmic explosions,” says co-author and astronomy student Zhenghai Liu of the University of Illinois in Urbana-Champaign.
In other words, if plutonium-244 and samarium-146 and can be found buried in the Devonian-Carboniferous border, the researchers say we’ll basically have our smoking gun: interstellar evidence that firmly involves a dying star like the trigger behind one of the Worst Deaths of All Time on Earth.
And we’ll never look at the sky the same way again.
The results are reported in PNAS.
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