A study has found that cosmic energy from supernova 2.6 million years ago may have contributed to hominin bipedalism. (Image: NASA)Walking on two legs was an evolutionary leap for the human ancestors, but it seems we have to thank the stars for this. According to new research, the cosmic energy bombarded by exploding stars might be the reason why humans are bipedal.
The research published in the Journal of Geology suggests that the energy released by supernovae eight million years ago (with a peak some 2.6 million years ago) may have triggered a chain of events that eventually became the reason ancient humans started walking on two legs.
The research titled “From cosmic explosions to terrestrial fires?” has been authored by Adrian L Melott, a professor at the University of Kansas in the US and Brian C Thomas, a professor at the Washburn University.
The paper claims that the radiation arriving from the cataclysmic explosions peaked about 2.6 million years ago. It initiated an avalanche of electrons in the lower atmosphere of Earth. This atmospheric ionisation, in turn, triggered an upsurge in cloud-to-ground lightning strikes, thus resulting in an increase in nitrate deposition and wildfires.
Wildfire and human bipedalism
It has been long argued that the evolution of hominin bipedalism (walking on two legs) has been a factor of increased savanna land in northeast Africa. The study says that the increased wildfires would have contributed to the transition from forest to savanna in the region. This, in turn, would have led to ancient humans learning to walk on two legs.
Melott says that it is thought there was already some tendency for hominins to walk on two legs, even before this event but they were mainly adapted for climbing around in trees.
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“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,” says Melott, adding that the human ancestors could see over the tops of grass and watch for predators, so the bipedalism became more and more dominant.
How supernovae events relate to wildfire
The study mentions that based on a “telltale” layer of iron-60 deposits lining the world’s sea beds, astronomers have high confidence supernovae exploded in Earth’s immediate cosmic neighbourhood (around 163 light years away) during the transition from the Pliocene Epoch to the Ice Age. The authors of the study calculated the ionisation of the atmosphere from cosmic rays which would have come from a supernova about as far away as the iron-60 deposits indicated.
“Usually, you don’t get lower-atmosphere ionisation 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,” says Melott.
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Melott and Thomas believe assert that more ionisation meant an abundance of electrons and more pathways for lightning strikes which would have spiked the worldwide upsurge in forest fires. The researcher found the proof of the link between the events in the discovery of carbon deposits found in soils corresponding with the timing of the cosmic-ray bombardment.
Melott says that there is no possibility of a similar event happening anytime soon. The nearest star that is capable of exploding into a supernova in the next million years is Betelgeuse. It is located at a distance of 652 light years away from Earth.
