Supernova may have killed Earth’s Devonian-era monstrous fish

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TORONTO – More than 350 million years ago, the Earth was ruled by fish, some measuring up to 10 meters in length. But a mass extinction spanning millions of years killed up to 80% of all species that existed at that time, ending the Devonian period.

Scientists have developed many theories over the years as to why this extinction could have happened, such as volcanic activity, meteorites or rapid global warming.

Now, new research points to a new possibility: what if a supernova was responsible?

An article published Tuesday in the Proceedings of the National Academy of Sciences of the United States of America (PNAS) details the brand new theory and how it could be proven – or excluded.

The Devonian period occurred around 416 million to 358 million years ago. The world was very different then, characterized by two supercontinents, Gondwana and Laurussia, which would eventually combine to form Pangea.

Part of the Paleozoic Era, the Devonian period is also referred to as the Age of Fish, as biodiversity exploded in the Earth’s oceans during this time. Shark ancestors originated in the Devonian, and a fossilized creature from the Devonian period found in the Canadian Arctic in 2004, called a tiktaalik, is believed to be a “vital link between fish and the first vertebrates to walk on land, ”According to National Geographic.

During the Late Devonian period, there was an enormous loss of biodiversity that occurred over millions of years. It is believed that two extinction pulses, the Kellwasser event and, about 10 million years later, the Hangenberg event, ended the Devonian period for good, leading the planet into the Carboniferous period.

The Hangenberg crisis refers to a confluence of events that had a catastrophic effect on living things during that time. There was a widespread problem with the oceans losing a high percentage of oxygen, called the ocean anoxic event, creating huge dead zones in the seas. There was also a dramatic drop in sea level around the same time.

According to Tuesday’s article, recent evidence suggests that the Hangenberg event at the end of the Devonian was also associated with a depletion of stratospheric ozone – the layer that filters out dangerous ultraviolet rays from the Sun.

The new research theorizes that a supernova millions of miles away could have bombarded the planet with ionizing radiation, causing ozone depletion.

A supernova is when a dying star of massive proportions explodes, creating either a neutron star or a black hole in its place, and launching a shock wave of charged elements, gases and particles into the galaxy.

Researchers believe that if a supernova is responsible, it would have been about 20 parsecs, or 66 light years, from Earth, “a little beyond the ‘destruction distance’ that would have precipitated full mass extinction. . ”

Many massive stars capable of producing supernovas live in the Milky Way. A remote supernova the researchers postulated sent cosmic rays to Earth for around 100,000 years.

“The intensity of cosmic rays is believed to be high enough to deplete the ozone layer and induce UV-B damage for thousands of years,” the researchers wrote.

They pointed out that while the depletion of the ozone layer caused by enhanced convection – one of the other theories surrounding extinction – is generally geographically limited and episodic, the depletion of the ozone layer caused by an supernova would lead to an extinction event.

Although ionizing radiation from space is known to be a possible cause of ozone depletion, research indicates that this theory has never been applied to this particular mass extinction before.

But is there a way to prove this theory? The researchers say there is, if we inspect the distinct layer of rock in the earth’s crust that corresponds to the Devonian period, where fossils and preserved materials can allow us to look at the extinction itself.

If a supernova caused by the collapse of a massive star’s core were close enough to cause this mass extinction, it would also have spread supernova “debris” above Earth in the form of “d-sized particles. ‘a micron or submicron created soon after the explosion’.

This would have left radioactive isotopes on Earth – distinct versions of the chemical elements that are unstable and emit radiation as they decay.

Different radioactive isotopes have different lifetimes, which means that “those whose lifetimes are comparable to the period since the event would provide appropriate signatures”, if they are found in fossils or in Devonian rocks. .

Researchers believe that two of the long-lived radioisotopes that could have been deposited on Earth – and are still detectable today – could be samarium-146 and plutonium-244.

The end of the Devonian period, brought on by numerous extinction events that severely reduce the level of biodiversity in Earth’s oceans, is still a mystery at this time. But if scientists can find these radioisotopes, it may mean that supernovas have played a bigger role in the history and evolution of our planet than we have ever known.

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