Life tries, but it does not work. As the period in late Devonian progressed, more and more living things became extinct, culminating in one of the largest mass extinction events our planet has ever seen, some 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 come from our solar system.
On the contrary, a study published in August last year, led by astrophysicist Brian Fields of the University of Illinois at Urbana-Champaign, suggests that this great extinguisher of life on earth could have been a distant and utterly strange phenomenon. a dying star far beyond the galaxy, many light years away from our own distant planet.
Mass deaths such as the extinction of the late Devonian are sometimes suspected to be caused by purely terrestrial causes: a devastating volcanic eruption, which, for example, suffocates the planet to lifelessness.
Or it could be a deadly visitor entering the city – a collision of the asteroid, like the one the dinosaurs took out. Death from space, however, can eventually 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 cruelly.”
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 may not have been the result of volcanism or an episode of global warming.
Instead, they suggest that the biodiversity crisis exposed in the geological report 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 the ozone of our planet. such a disastrous effect.
This may be the first time such a statement has been made for the extinction of the late Devonian, but scientists have long considered the potentially deadly effects of supernovae near Earth in this kind of context.
The speculation that supernovae can cause mass extinctions dates back to the 1950s. In recent times, researchers have discussed the estimated ‘dead 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 suggest that exploding stars could have even more detrimental consequences for life on Earth through a possible combination of immediate and long-lasting effects.
“Supernovae (SNs) 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 and forms a shock that drives particle acceleration. In this way, SNe produces cosmic rays, that is, atomic nuclei that are accelerated to high energies. These charged particles are magnetically confined in the SN residue. , and they are expected to bathe the earth for ~ 100 ky [approximately 100,000 years]. “
The cosmic rays, according to the researchers, may be strong enough to deplete the ozone layer and cause long-term radiation damage to life forms in the Earth’s biosphere – roughly equivalent to the loss of diversity and deformation in ancient plant spores found in the deep rock of the Devonian – Carbon border, laid about 359 million years ago.
Of course, this is just a hypothesis for now. At present we have no evidence that can confirm that a distant supernova (or supernova) was the cause of the extinction in late Devonian. But maybe we can find something as good as proof.
In recent years, scientists investigating the prospect of supernovae near Earth as a basis for mass extinction have been searching for traces of ancient radioactive isotopes that could only be deposited on Earth via exploding stars.
One isotope in particular, iron-60, was the focus of much research and has been found in numerous places on earth.
However, in the context of the Late Devonian extinction, other isotopes would be strongly indicative of 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,” explained co-author and astronomy student Zhenghai Liu of the University of Illinois Urbana-Champaign.
In other words, if plutonium-244 and samarium-146 and can be found in the Devonian carbon-like boundary, the researchers say we will basically have our smoke gun: interstellar evidence that a dying star is the trigger behind one of Earth’s worst deaths ever.
And we will never look up at the sky in the same way again.
The findings were reported in PNAS.
A version of this article was first published in August 2020.