Life tried, but it did not work. As the Late Devonian period approached, more and more living things died out, culminating in one of the greatest events of mass extinction our planet has ever witnessed, some 359 million years ago.
The culprit responsible for so many deaths may not have been local, scientists now say. In fact, it might not even come from our solar system.
After all, a new study led by astrophysicist Brian Fields of the University of Illinois Urbana-Champaign suggests that this large extinguishing device of life on Earth could have been a distant and completely strange phenomenon – a dying star, exploding far across the galaxy, many light years away from our own planet at a distance.
It is sometimes thought that mass deaths such as the Late Devonian extinction are triggered by exclusively terrestrial causes: a devastating volcanic eruption, for example, which shocks the planet into lifelessness.
Or it could be a deadly visitor burning out of the city – an asteroid collision, like the kind that the dinosaurs caught. Death from space, however, could eventually come from farther distant places.
“The overwhelming message of our study is that life on earth does not exist in isolation,” Fields says.
“We are citizens of a larger cosmos, and the cosmos intervenes in our lives – often imperceptibly, but sometimes cruelly.”
In their new work, Fields and his team explore the possibility that the dramatic decline in ozone levels coinciding with the Late Devonian extinction may not have been a result of volcanism as an episode of global warming.
Instead, they suggest that it is possible that the biodiversity crisis exposed in the geological record could have been caused by astrophysical sources, and speculate that the radiation effects of a supernova (or more) may have been about 65 light-years from Earth. the ozone of our planet depleted such a disastrous effect.
It may be the first time such a statement has been made before Late Devonian extinction, but scientists have long considered the potentially fatal consequences of near-Earth supernovae in this kind of context.
Speculations that supernovae could carry out mass extinctions date back to the 1950s. In more recent times, researchers have debated the estimated ‘kill distance’ from these explosive events (with estimates ranging from 25 to 50 million light-years).
In their new estimates, however, Fields and his co-authors suggest that exploding stars could have even more damaging effects on life on Earth, through a possible combination of both direct and long-term life effects.
“Supernovae (SNe) are fast sources of ionizing photons: extreme UV, X-rays, and gamma rays,” the researchers explain in their paper.
“Over longer time scales, the explosion collides with ambient gas, forming a shock that drives particle acceleration. In this way, SNe produce cosmic rays, which are atomic nuclei that are accelerated to high energy. These charged particles become magnetic contained in the SN remainder, and are expected to bathe the Earth for ~ 100 ky [approximately 100,000 years]. “
These cosmic rays, the researchers say, could be strong enough to remove the ozone layer and cause long-term irradiation of life forms in the Earth’s biosphere – which is roughly parallel to evidence of both the loss of diversity and deformation in ancient plant spores. which is in the deep rock of the Devonian – Carboniferous border, built about 359 million years ago.
Of course, it’s just a hypothesis for now. At present we have no evidence that can confirm that a distant supernova (or supernovae) was the cause of the Late Devonian extinction. But we might find something almost as good as evidence.
In recent years, scientists have studied the prospect of supernovae in the Earth’s orbit as a basis for mass extinctions, searching for traces of ancient radioactive isotopes that could only be deposited on Earth by exploding stars.
One isotope in particular, iron-60, has been the focus of much research, and has been found at various locations on Earth.
In the context of the Late Devonian extinctions, however, other isotopes could strongly suggest the extinction-by-supernova hypothesis proposed by Fields and his team: plutonium-244 and samarium-146.
“None of these isotopes occur naturally on Earth today, and the only way they can get here is through cosmic explosions,” explains co-author and astronomy student Zhenghai Liu of the University of Illinois at 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 basically have our smoking pistol: interstellar evidence that a dying star firmly implies when the trigger behind one of Earth’s worst-ever death-offs.
And we will never look at the skies in exactly the same way again.
The findings are reported in PNAS.
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