Ancient supernova led humans to walk upright, scientists claim

James Marshall
May 29, 2019

The authors of a recently published study assert that, at the peak of the bombardment, roughly 2.6 million years ago, the radiation was partially responsible for reshaping the environment of northeast Africa, where humanity's ancestors where developing.

Humans and our primate relatives differ in many ways, but the fact we walk on two legs is one of the most obvious.

"By 3.6 million years ago, we have proficient bipeds, like 'Lucy, ' and by 1.6 million years ago, [we have] obligate bipeds very similar to us", he explained. Many factors likely contributed to the evolution of bipedalism, a process that began many millions of years before these stellar explosions took place, one expert told Live Science. According to a hypothesis astronomers have laid out in a new paper, the exploding stars at the end of their lives - supernovae - could have bathed Earth in cosmic radiation, beginning around 8 million years ago, and peaking around 2.6 million years ago. 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.

Early humans then had to adapt from living in and around trees to surviving in open savannas, meaning the ability to cross exposed grassland at speed and spot predators above the vegetation became crucial. After this conversion to savannah, they would much more often have to walk from one tree to another across the grassland, and so they become better at walking upright.

"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 about.

'It appears this was the closest one in a much longer series.

While the scientists could not calculate precisely how many additional lightning events would result from a 50-fold boost in ionization, "the potential is there for a large increase", they wrote in the study.

The overabundance of unbound electrons saturating the lower atmosphere in the wake of a supernova would allow this process to start faster, thus allowing for a greater number of cloud-to-surface lightning bolts. In turn, electrons help carry lightning from the clouds to the ground, so these loose electrons would have made lightning strikes a lot easier.

"So, it has to build up high voltage before electrons start moving".

What's more, the destructive power and scope of those hypothetical wildfires hinges on a significant increase in lightning as a result of the supernovas, a variable that the researchers were "unable to estimate", they wrote in the study. This process could lead to a dramatic uptake in the amount of lightning bolts. Global carbon deposits confirm the link between an ancient abundance of fires and the cosmic-ray bombardment.

The first evidence for bipedalism in ancient humans dates to approximately 7 million years ago, and the transition to full bipedalism was well underway by around 4.4 million years ago, said Harcourt-Smith, who was not involved in the study. That's thought to be related to human evolution in northeast Africa.

"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", he added. The nearest star capable of exploding into a supernova in the next million years is Betelgeuse, some 200 parsecs (652 light years) from Earth.

"Betelgeuse is too far away to have effects anywhere near this strong", Melott said. Worry about solar proton events. "Just imagine months without electricity".

Other reports by Click Lancashire

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