Life tried, but it didn’t work. As the Late Devonian period lengthened, more and more living things died there, culminating in one of the largest mass extinction events our planet has ever experienced, approximately 359 million years ago.
According to scientists, the culprit for so much death has not been local. In fact, it may not even have come from our solar system.
Rather, a study published in August last year, led by astrophysicist Brian Fields of the University of Illinois Urbana-Champaign, suggests that this large extinguisher of life on Earth may have been a distant phenomenon. and completely strange: a dying star that would explode much galaxy, many light years away from our own remote planet.
Mass deaths such as the extinction of the late Devonian are sometimes believed to be caused by exclusively terrestrial causes: a devastating volcanic eruption, for example, that suffocates the lifeless planet.
Or, it could be a deadly visitor entering the city: a collision of asteroids, like the one that took out the dinosaurs. Death by space, however, could ultimately come from much more remote 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 work, Fields and his team explore the possibility that the dramatic decline in ozone levels coinciding with the extinction of the late Devonian would not have been 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 record may have been caused by astrophysical sources, speculating that the radiation effects of a supernova (or multiple) about 65 light-years from Earth could having been the one who depleted the ozone of our planet. such a disastrous effect.
This may be the first time such an explanation has been presented for the extinction of the late Devonian, but scientists have long considered the potentially deadly repercussions of supernovae close to Earth in this type of context.
Speculation that supernovae could cause mass extinctions dates back to the 1950s. In more recent times, researchers have debated the estimated “death distance” of these explosive events (with estimates ranging from 25 to 50 million light-years).
In their recent estimates, however, Fields and his co-authors propose that exploding stars even further away could have harmful effects on life on Earth, through a possible combination of both instantaneous and long-lasting effects.
“Supernovae (SNe) are fast sources of ionizing photons: ultraviolet rays, X-rays, and gamma rays,” the researchers explain in their work.
“Over longer periods of time, the explosion collides with the surrounding gas, forming a collision that drives the acceleration of the particles. In this way, SNe produce cosmic rays, that is, atomic nuclei accelerated to high These charged particles are magnetically confined inside the remnant SN, and are expected to bathe the Earth for ~ 100 ky. [approximately 100,000 years]. “
These cosmic rays, according to researchers, could be strong enough to deplete the ozone layer and cause long-lasting radiation damage to life forms in the Earth’s biosphere, roughly paralleling the evidence of both loss of diversity and deformations in ancient plant spores found in the deep rock of the Devonian-Carboniferous boundary, located approximately 359 million years ago.
Of course, for now it’s just a hypothesis. Currently, we have no evidence that can 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 proof.
In recent years, scientists who examined the prospect of supernovae close to Earth as a basis for mass extinctions have been looking for traces of ancient radioactive isotopes that could only have been deposited on Earth by exploding stars.
One particular isotope, iron-60, has been the focus of much research and has been found in numerous places on Earth.
In the context of the late Devonian extinction, however, other isotopes would be strongly indicative of the supernova extinction 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,” explained 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 at the Devonian-Carboniferous boundary, researchers say we will basically have our smoking weapon: interstellar evidence that strongly involves a dying star as a trigger behind of one of the worst deaths on Earth.
And we will not look at the sky the same way again.
The findings were reported to PNAS.
A version of this article was first published in August 2020.