The authors of a new study argue an ancient supernova triggered a series of events that ended with early humans walking upright.

According to the latest research, published this week in the Journal of Geology, a series supernovae spawned cosmic radiation that began bombarding Earth some 8 million years ago. The radiation peaked 2.6 million years ago, scientists claim.

The constant supply of cosmic particles ionized the atmosphere, scientists claim. Authors of the new paper hypothesize ionization increased the rate of loud-to-ground lightning strikes, sparking forest fires across the globe.

"It is thought there was already some tendency for hominins to walk on two legs, even before this event," Adrian Melott, professor emeritus of physics and astronomy at the University of Kansas, said in a news release. "But they were mainly adapted for climbing around in trees. After this conversion to savanna, they would much more often have to walk from one tree to another across the grassland, and so they become better at walking upright. They could see over the tops of grass and watch for predators. It's thought this conversion to savanna contributed to bipedalism as it became more and more dominant in human ancestors."

Scientists found evidence of large supernovae explosions, originating from 160 light-years away, on the ocean floor. Iron-60 deposits found in seafloor samples all over the world suggest the supernovae exploded during the transition from the Pliocene Epoch to the Ice Age.

"We calculated the ionization of the atmosphere from cosmic rays which would come from a supernova about as far away as the iron-60 deposits indicate," Melott said. "It appears that this was the closest one in a much longer series. We contend it would increase the ionization of the lower atmosphere by 50-fold. Usually, you don't get lower-atmosphere ionization because cosmic rays don't penetrate that far, but the more energetic ones from supernovae come right down to the surface -- so there would be a lot of electrons being knocked out of the atmosphere."

The lower-atmosphere ionization resulted in a glut of electrons, scientists claim. The extra electrons formed accessible electrical pathways from cloud to ground, encouraging an uptick in lightning strikes.

"Ordinarily, in the lightning process, there's a buildup of voltage between clouds or the clouds and the ground -- but current can't flow because not enough electrons are around to carry it. So, it has to build up high voltage before electrons start moving," Melott said.

Supernovae-triggered ionization and the subsequent flood of electrons lowered the voltage threshold. More lightning strikes caused an increased in wildfires, according to researchers. Global carbon deposits confirm the link between an ancient abundance of fires and the cosmic-ray bombardment.

"The observation is that there's a lot more charcoal and soot in the world starting a few million years ago," Melott said. "It's all over the place, and nobody has any explanation for why it would have happened all over the world in different climate zones."

The increase in forest forests, combined with global climate change, encouraged the formation of grasslands. Open landscapes required travel by two feet. Though researchers have never before linked bipedalism with cosmic rays, previous studies have suggested the transition from woodlands to savanna encouraged the evolution of upright walking.

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