Trending Science: Did exploding stars lead humans to walk on two legs?

Can a supernova – the biggest explosion that can occur in space – that bombarded Earth with cosmic energy millions of years ago have prompted the ancestors of humans to rise up on two legs?

According to findings in ‘The Journal of Geology’, a supernova occurred 8 million years ago, with a peak of activity 2.6 million years ago, that brought electrons into the lower atmosphere. This contribution of particles was at the source of a series of events that led to bipedalism. Cosmic rays hammered the planet, ionising the atmosphere and making it more conductive.

This occurrence likely led to lightning strikes that set off forest fires around the world. It’s supported by the discovery of carbon deposits found in soils that correspond with the supernova timing. “There’s a lot more charcoal and soot in the world starting a few million years ago,” lead author Prof. Adrian Melott from the Department of Physics and Astronomy at the University of Kansas, told ‘CNN’. “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. This could be an explanation. That’s thought to be related to human evolution in northeast Africa. Specifically, in the Great Rift Valley where you get all these hominin fossils.” These fires turned some of the forests into savannahs in north-east Africa. The ancestors of Homo sapiens became bipedal to adapt to this environment.

Thank exploding stars for walking on two feet today?

“It is thought there was already some tendency for hominins to walk on two legs, even before this event,” explained Prof. Melott. “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. It’s thought this conversion to savanna contributed to bipedalism as it became more and more dominant in human ancestors.”

“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,” Prof. Melott said.

“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,” Prof. Melott added. “So, it has to build up high voltage before electrons start moving. Once they’re moving, electrons knock more electrons out of more atoms, and it builds to a lightning bolt. But with this ionization, that process can get started a lot more easily, so there would be a lot more lightning bolts.”

Speaking to the British newspaper ‘The Guardian’, Prof. Melott and the American research team acknowledge that more research is needed to understand if cosmic rays really do propel lightning: “If the lightning–cosmic ray connection turns out to be incorrect, this whole thing falls apart.”