Life tried, but it didn’t work. As the Late Devonian period extended, more and more living things disappeared, culminating in one of the largest mass extinction events our planet has ever witnessed, about 359 million years ago.
The culprit responsible for so much death may not have been local, scientists say. In fact, it may not have even come from our solar system.
Rather, a study published in August last year by astrophysicist Brian Fields of the University of Illinois Urbana-Champaign suggests that this great life-extinguisher on Earth could have been a distant and completely alien phenomenon – a dying star. , which explodes across the galaxy, many light-years away from our distant planet.
Sometimes mass deaths, such as the late Devonian disappearance, are thought to be triggered solely by terrestrial causes: a devastating volcanic eruption, for example, that suffocates the planet in its absence.
Or, it could be a deadly visitor approaching from outside the city – an asteroid collision, like the one that brought out the dinosaurs. However, death in space could come from more distant places.
“The overall message of our study 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 fiercely.”
In their new paper, Fields and his team explore the possibility that the dramatic drop in ozone levels that coincided with the late disappearance of the Devonian may not have been the result of volcanism or a global warming episode.
Instead, they suggest that the biodiversity crisis exposed in the geological record may have been caused by astrophysical sources, speculating that the effects of radiation from a supernova (or multiple) about 65 light-years from Earth could have been what depleted the ozone of our planet. such a disastrous effect.
It may be the first time such an explanation has been put forward for late Devonian extinction, but scientists have long considered the potentially deadly repercussions of supernovae near Earth in this context.
Speculation that supernovae could trigger mass extinctions dates back to the 1950s. In more recent times, researchers have debated the estimated “killing 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 propose that the explosion of even more distant stars could have detrimental effects on life on Earth, through a possible combination of both instantaneous and long-term effects. .
“Supernovae (SNe) are prompt sources of ionizing photons: extreme ultraviolet, X-rays and gamma rays,” the researchers explain in their paper.
“Over longer periods of time, the explosion collides with the surrounding gas, forming a shock that accelerates the particles. In this way, SNe produces cosmic rays, ie atomic nuclei accelerated to high energies. These charged particles are magnetically limited inside the remnant SN , and is expected to bathe the Earth for ~ 100 ky [approximately 100,000 years]. “
Researchers claim that these cosmic rays could be strong enough to deplete the ozone layer and cause long-term radiation damage to life forms in the Earth’s biosphere – which parallels the evidence for both loss of diversity and deformation in the Earth’s biosphere. spores of ancient plants found in the deep rock of the Devonian-Carboniferous border, laid about 359 million years ago.
Of course, it’s just a hypothesis for now. At present, we have no evidence to confirm that a distant supernova (or supernova) was the cause of the late Devonian extinction. But we could find something almost as good as the evidence.
In recent years, scientists examining the perspective of supernovae near Earth as a basis for mass extinctions have looked for traces of ancient radioactive isotopes that could have been stored on Earth only by exploding stars.
One isotope in particular, iron-60, has been at the center of much research and has been found in many locations on Earth.
In the context of the late Devonian extinction, however, other isotopes would be strongly indicative of the supernova extinction hypothesis presented 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,” said 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 boundary, researchers say we will essentially have our smoking weapon: interstellar evidence that firmly involves a dying star as a trigger behind one of the The worst deaths 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.