The radiation would have given animals the equivalent dose of one additional CT scan in radiation per year. CT scans take X-ray images from several angles to let doctors look inside tumors and other objects. The night sky also would have bathed in blue light from the explosions, making it difficult for animals to sleep.
Some researchers have speculated that there could be a link between increased cosmic rays and a cooler climate on Earth, although that link isn't proven for sure. (Simply put, the theory associates cosmic rays with aerosols, which could produce clouds, which in turn reduces the amount of solar radiation on the surface.) If a connection could be made, Melott said it is possible the supernovae were associated with a known, smaller mass extinction 2.59 million years ago when Earth went through repeated ice ages.
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"There was climate change around this time," Melott said. "Africa dried out, and a lot of the forest turned into savannah. Around this time and afterwards, we started having glaciations - ice ages - over and over again, and it's not clear why that started to happen. It's controversial, but maybe cosmic rays had something to do with it."
The research is available on preprint website arXiv and has been accepted in Astrophysical Journal Letters. It was led by Brian Thomas, a physicist and astronomer at Washburn University in Kansas.
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