Life tried, but it didn’t work. As the Late Devonian period continued, more and more living things became extinct, culminating in one of the greatest mass extinction events our planet ever experienced, about 359 million years ago.
The culprit responsible for so many deaths may not have been local, scientists say. In fact, it may not even have originated from our solar system.
Instead, a study published last August, led by astrophysicist Brian Fields of the University of Illinois Urbana-Champaign, suggests that this great fire extinguisher of life on Earth could be a distant and utterly strange phenomenon – a dying star that exploded far over the Earth. galaxy, many light years from our own distant planet.
Mass extinctions, such as the late Devonian extinction, are sometimes thought to be caused solely by terrestrial causes: a devastating volcanic eruption, for example, choking the planet in lifelessness.
Or it could be a deadly visitor storming into town from outside – an asteroid collision, like the kind that knocked out the dinosaurs. However, death from space could eventually come from far more distant places.
“The overarching message of our research is that life on Earth does not exist in isolation,” Fields said in 2020.
“We are citizens of a larger cosmos, and the cosmos intervenes in our lives – often imperceptibly, but sometimes savage.”
In their new work, Fields and his team investigate the possibility that the dramatic drop in ozone concentrations that coincided with the late Devonian extinction was not due to volcanism or an episode of global warming.
Instead, they suggest that it is possible that the biodiversity crisis uncovered in the geologic data may have been caused by astrophysical sources, and speculate that the radiative effects of a supernova (or several) about 65 light-years from Earth may be the ozone layer of our planet to such a disastrous effect.
It may be the first time such an explanation has been offered for the late Devonian extinction, but scientists have long pondered the potentially deadly consequences of near-terrestrial supernovae in this kind of context.
The speculation that supernovae could cause mass extinctions dates back to the 1950s. In more recent times, researchers have debated the estimated kill distance of these explosive events (with estimates ranging from 25 to 50 million light years).
However, in their recent estimates, Fields and his co-authors argue that exploding stars from even more distant could have detrimental effects on life on Earth, through a possible combination of both immediate and long-lived effects.
“Supernovae (SNe) are direct sources of ionizing photons: extreme UV, X-ray and gamma rays,” the researchers explain in their paper.
Over longer timescales, the explosion collides with the surrounding gas and creates a shock that causes the particle acceleration. In this way, SNe produces cosmic rays, that is, atomic nuclei that are accelerated to high energies. These charged particles are magnetically trapped in the SN remnant. , and are expected to bathe the Earth ~ 100 ky [approximately 100,000 years]
This cosmic rays, the researchers argue, could be strong enough to deplete the ozone layer and cause long-term radiation damage to life forms in Earth’s biosphere – roughly consistent with evidence of both loss of diversity and distortions in ancient plant tracks. found in the biosphere. deep rock of the Devonian-Carboniferous border, laid about 359 million years ago.
It’s just a hypothesis for now, of course. Currently, we have no evidence to confirm that a distant supernova (or supernova) was the cause of the late Devonian extinction. But we may be able to find something almost as good as evidence.
In recent years, scientists investigating the prospect of near-Earth supernovae as the basis for mass extinctions have been looking for traces of ancient radioactive isotopes that could only have been deposited on Earth through exploding stars.
One isotope in particular, iron-60, has been the focus of much research and has been found in numerous locations on Earth.
However, in the context of the late Devonian extinction, other isotopes would be strongly indicative of the supernova extinction hypothesis advanced by Fields and his team: plutonium-244 and samarium-146.
“None of these isotopes occur naturally on Earth, and the only way they can get here is through cosmic explosions,” explains study co-author and astronomy student Zhenghai Liu of the University of Illinois Urbana-Champaign.
In other words, if plutonium-244 and samarium-146 can be found buried in the Devonian-Carboniferous border, the researchers say we do in fact have our smoking gun: interstellar evidence implying a dying star as the trigger behind one of The worst deaths ever on Earth.
And we will never look at the sky the same way again.
The findings were reported in PNAS
A version of this article was first published in August 2020.