A supernova explosion coinciding with the start of Pleistocene period could have wiped out large ocean creatures in a mass extinction event about 2.6 million years ago. That's the suggestion of a new study led by scientists from the University of Kansas.
About 2.6 million years ago, Earth witnessed a mass extinction event that wiped out large numbers of marine creatures, especially the largest ocean animals, including the megalodon - a giant shark, about the size of a school.
Scientists suspect this extinction event likely coincided with a supernova explosion occurring about 150 light years away from Earth.
"I've been doing research like this for about 15 years, and always in the past it's been based on what we know generally about the universe - that these supernovae should have affected Earth at some time or another," said Professor Adrian Melott from the University of Kansas, the lead author of the study.
"This time, it's different. We have evidence of nearby events at a specific time. We know about how far away they were, so we can actually compute how that would have affected the Earth and compare it to what we know about what happened at that time - it's much more specific."
According to scientists, a big supernova explosion might have bathed the planet in cosmic rays, showering it with iron-60, a radioactive isotope. Scientists have found high concentration of this isotope in ancient seabed deposits across the globe.
Scientists believe this isotope most likely came from a supernova as iron-60 has a half-life of 2.6 million years and naturally decays into cobalt-60 then, within five years, to a stable nickel-60. Hence, any such isotope of iron formed on Earth would have disappeared long time back.
The study also indicates that there were actually a series of supernova events around the same time, but that one was unusually powerful and close. These events showered on Earth, not only iron-60 isotopes but also heavy particles known as muons.
Muons are a couple of hundred times bigger than an electron, and are highly penetrating. They can be dangerous for living creatures when encountered in large volumes, causing mutations and cancer in the cells. Larger animals were specifically at risk of those mutations as they had more cells for muons to interact with.
The massive size of megalodon would have made it particularly vulnerable to exposure with muons, scientists believe.
They also point out that the 'local bubble' in the interstellar medium would have caused the cosmic rays to bounce off the sides. Therefore, the cosmic-ray bath would have lasted for about 10,000 to 100,000 years.
Melott's co-authors in the study were Laura Paulucci of Federal University of ABC in Brazil, and Franciole Marinho of Federal University of São Carlos, also in Brazil.
The findings of the study are published in the journal Astrobiology.
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