The Earth was ruled by fish more than 350 million years ago. Some of the fish were up to 10 meters long. The Devonian Period was brought down by mass extinction stretching across millions of years killing up to 80% of all species that existed at that time. Volcanic activity, meteorites, or rapid global warming are among the numerous theories brought by scientists to explain why this extinction might have occurred.
Currently, there is a new perspective: what if a supernova was responsible? On Tuesday, there was a paper published in the Proceedings of the National Academy of Sciences of the United States of America (PNAS) explaining the new theory and the way it could feasibly be proven or ruled out. During the Devonian Period, which occurred from roughly 416 million to 358 million years ago, the world looked vastly different. It was characterized by two supercontinents, Gondwana and Laurussia, combining later to form Pangaea.
The Age of Fishes was part of the Paleozoic Era, the Devonian Period. At that time, biodiversity exploded within Earth’s oceans. According to the National Geographic, a fossilized creature from the Devonian period which was found in the Canadian Arctic in 2004, called a Tiktaalik, is thought to be a “vital link between fish and the first vertebrates to walk on land as the ancestors of sharks had their beginning in the Devonian.” There was a huge loss of biodiversity that occurred over millions of years during the Late Devonian period. Two extinction pulses that are thought to have finished off the Devonian period for good were the Kellwasser event and, around 10 million years, and later, the Hangenberg event.
The Hangenberg Crisis is the convergence of events that had a catastrophic effect on the living things of that time. There was a creation of massive dead zones within the seas after a widespread issue with the oceans losing a high percentage of oxygen, named ocean anoxic event. The paper also indicated that new evidence has shown that the Hangenberg event, at the end of the Devonian, was also linked to a depletion of the stratospheric ozone. What caused the depletion of the ozone was a supernova, which was millions of miles, after bombarding the planet with ionizing radiation. A supernova is a massive explosion of a dying star, creating either a black hole in its place or a neutron star and firing a shock wave of elements into the galaxy.
The scholars think that it would have been within around 20 parsecs, or 66 lightyears of Earth if a supernova was responsible. Many massive stars that can produce supernovas live in the Milky Way. The researchers wrote that the cosmic ray intensity would be high enough to deplete the ozone layer and induce UV-B damage for thousands of years. They also indicated that one of the other theories surrounding the extinction is generally geographically limited and episodic. They stated that this theory has never been applied to this particular mass extinction before and if they inspect the distinct layer of rock in the Earth’s crust that corresponds to the Devonian Period; they can be able to peer into the extinction itself.
They guess that samarium-146 and plutonium-244 are the two of the long-lived radioisotopes that could’ve been deposited on Earth and would be still detectable today. They said it is a mystery for the end of the Devonian Period, spurred on by numerous extinction events that severely cut down the level of biodiversity in Earth’s oceans. It may mean that supernovas have played a greater role in our planet’s history and evolution than we ever knew if scientists can find these radioisotopes.