Life tried, but it didn’t work. As the late Devonian period drags on, more and more living things are dying, culminating in one of the largest mass extinctions our planet has witnessed, about 359 million years ago.
The culprit for so many deaths may not have been local, scientists say. In fact, it may not even come from our solar system.
Rather, a study published last August by astrophysicist Brian Fields of the University of Illinois at Urbana-Champaign suggested that this great fire extinguisher on Earth may have been a distant and completely alien phenomenon – a dying star exploding far away. a galaxy many light-years away from our own distant planet.
Mass extinctions, such as the late Devonian extinction, are sometimes thought to be caused by purely terrestrial causes: a devastating volcanic eruption, for example, that suffocates the planet with lifelessness.
Or it could be a deadly visitor invading outside the city ̵
“The overarching 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 interferes with our lives – often imperceptibly, but sometimes fiercely.”
In their new work, Fields and his team explore the possibility that the dramatic drop in ozone levels, coinciding with the extinction at the end of the Devonian, was not the result of volcanism or an episode of global warming.
Instead, they suggest that the biodiversity crisis set out in the geological record may have been caused by astrophysical sources, speculating that the radiation effects of a supernova (or multiple) about 65 light-years from Earth may have been. which has depleted our planet’s ozone to such a catastrophic effect.
This may be the first time such an explanation has been given for the late Devonian extinction, but scientists have long considered the potentially deadly effects of supernovae near Earth in this context.
Speculation that supernovae could cause mass extinctions dates back to the 1950s. More recently, researchers have been discussing the approximate “killing distance” of these explosive events (with estimates ranging between 25 and 50 million light-years).
However, in their latest assessments, Fields and his co-authors suggest that blowing up stars from even further away could have detrimental effects on life on Earth, through a possible combination of both immediate and long-term effects.
“Supernovae (SNe) are fast sources of ionizing photons: extreme UV, X-rays and gamma rays,” the researchers explained in their report.
“On longer time scales, the explosion collides with the surrounding gas, creating a shock that drives the acceleration of the particles. In this way, SNe produces cosmic rays, ie atomic nuclei accelerated to high energies. These charged particles are magnetically enclosed in the rest of the SN, and are expected to bathe the Earth for ~ 100 ky [approximately 100,000 years]. “
Researchers claim that these cosmic rays could be strong enough to destroy the ozone layer and cause long-term radiation damage to life forms in the Earth’s biosphere – roughly consistent with evidence of both loss of diversity and deformation in ancient times. plant spores found in a deep Devonian-Carboniferous rock deposited about 359 million years ago.
Of course, for now this is just a hypothesis. We currently have no evidence to support that a distant supernova (or supernova) was the cause of the Late Devonian extinction. But we can find something almost as good as the proof.
In recent years, scientists studying the prospect of near-Earth supernovae as the basis for mass extinction have been looking for traces of ancient radioactive isotopes that could only be deposited on Earth by exploding stars.
In particular, one isotope, iron-60, has been the focus of much research and has been found in many places on Earth.
However, in the context of the Late Devonian extinction, other isotopes would be highly 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 they can get here is through space explosions,” said co-author and astronomy student Jenhai Liu of the University of Illinois Urbana-Champaign.
In other words, if plutonium-244 and samarium-146 can be found buried in the Devon-Carbon boundary, researchers say we’ll basically have our smoking gun: interstellar evidence that firmly includes a dying star as the trigger behind one of Nye -the worst extinction of the Earth.
And we will never look at the sky in exactly the same way again.
The findings were reported in PNAS.
A version of this article was first published in August 2020.