Life is working hard, but not successful. With the passing of the late Devonian period, more and more creatures became extinct, which eventually led to one of the most severe extinction events experienced by our planet approximately 359 million years ago.
Scientists say that the culprit responsible for so many deaths may not be locals. In fact, it may not even come from our solar system.
In contrast, a study published in August last year by astrophysicist Brian Fields of the University of Urbana-Champaign in Illinois showed that this great fire extinguisher on Earth may be a remote and complete It was an alien phenomenon-a dying star that exploded far across the earth. The Milky Way is many light years away from our own remote planet.
Sometimes mass deaths such as late Devonian extinctions are thought to be caused entirely by terrestrial causes: for example, a devastating volcanic eruption made the planet lifeless.
Or, it could be a deadly visitor breaking in from outside the city-an asteroid collision, like the one knocked out of a dinosaur. However, death in space may eventually come from more distant places.
Fields said in 2020: “The overall message of our research is that life on earth does not exist in isolation.”
“We are citizens of a larger universe, and the universe interferes with our lives-usually imperceptibly, but sometimes cruel.”
In their new work, Fields and his team explored the possibility of a sharp drop in ozone levels that coincided with the late Devonian extinction, which may not be the result of volcanic eruptions or global warming.
On the contrary, they believe that the biodiversity crisis exposed in the geological record may be caused by astrophysical sources, and speculate that the radiation effect from a supernova (or more) about 65 light-years from the earth may have exhausted our planet Ozone, such a catastrophic effect.
This may be the first such explanation for the extinction in the late Devonian, but scientists have long been considering the potentially fatal impact of near-Earth supernovae in this situation.
Speculation that supernovae might cause mass extinction can be traced back to the 1950s. In the most recent time, researchers have debated the estimated “distance to kill” of these explosions (estimated range is 25-50 million light-years).
However, in the latest estimate by Fields and his colleagues, by combining the instantaneous effect and the longevity effect, making the star explode further away may have a harmful effect on life on Earth.
The researchers explained in the paper: “Supernova (SNe) is a rapid source of ionizing photons: extreme ultraviolet, X-rays and gamma rays.”
“In a longer time frame, the explosion collides with the surrounding gas, forming an impact, pushing the particles to accelerate. In this way, SNe produces cosmic rays, that is, the nucleus is accelerated to high energy. These charged particles are magnetically confined in the SN residue. And is expected to bathe on the earth for about 100 ky [approximately 100,000 years]. “
Researchers believe that these cosmic rays may be strong enough to deplete the ozone layer and cause long-term radiation damage to life forms in the Earth’s biosphere, which is roughly similar to the evidence of diversity loss and deformation found in ancient biological spores. The deep rocks of the Devonian-Carboniferous boundary were laid about 359 million years ago.
Of course, this is just a hypothesis for now. At present, we do not have any evidence to prove that distant supernova (or supernova) was the cause of the extinction in the late Devonian. But we may be able to find something almost as good as the evidence.
In recent years, scientists who study near-Earth supernovae as the basis for mass extinction have been looking for traces of ancient radioisotopes, which can only be deposited on the earth by exploding stars.
In particular, one isotope, iron 60, is the focus of many studies and has been found in many places on the earth.
However, in the context of the late Devonian extinction, other isotopes will strongly indicate the supernova extinction hypothesis proposed by Fields and his team: p 244 and sa 146.
Astronomy student Liu Zhenghai, a co-author of the University of Illinois at Urbana-Champaign, explained: “Nowadays, none of these isotopes exist naturally on the earth. The only way for them to reach the earth is through the explosion of the universe.”
In other words, if can 244 and sa 146 can be found buried in the Devonian-Carboniferous boundary, the researchers say we will basically have our smoking gun: interstellar evidence firmly suggests that a dying star is among them One trigger point. The worst death in the history of the earth.
And we will never look up at the sky in exactly the same way again.
The findings are reported in NASA.
The version of this article was first published in August 2020.