Ancient Supernovae Could Be The Reason We Walk on Two Legs

A recent paper published in the Journal of Geology makes the claim that ancient supernovae might have led to our distant ancestors walking on two legs. This is one of the characteristic features of our species and lineage and allowed our hands to be freed to kick-start our astronomical technological development.

They believe they have found evidence that ancient supernovae set off a chain of events that eventually led to widespread wildfires around the globe. This may well be the cause for the formation of large expanses of savanna to open up, leading to the eventual adaption of bipedalism in human ancestors.

The idea that our ancient ancestors developed bipedalism as an evolutionary adaptation to this unique habitat is not a new one. And this new paper might offer an interesting underlying cause. 

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What is the link between supernovae and its effects on human ancestral evolution?

Within the paper in the Journal of Geology, researchers point out that the Earth appears to have been bombarded by the cosmic energy from supernovae starting around 8 million years ago. This activity, they claim, also appears to have peaked around 2.6 million years ago.

As the cosmic energy from these supernovae reached Earth it would have created an avalanche of elections in the lower atmosphere of our planet. This, they claim, would have led to atmospheric ionization that, most likely, triggered an unprecedented increase in cloud-to-ground lighting strikes.

If true, it would not be unfeasible that this would have resulted in the formation of widespread wildfires around the plant. Ancient forests would have been burned to the ground created the savannas common to the era. 

"It is thought there was already some tendency for hominins to walk on two legs, even before this event," explained lead author Adrian Melott, professor emeritus of physics & astronomy at the University of Kansas.

"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." he added. 

What evidence do they have for this bold claim?

The scientists reached their conclusion after finding a "telltale" layer of iron-60 in deposits of the time on sea beds around the globe. Astronomers also believe, with very high confidence, that supernovae occurred pretty close to Earth at this time.

By pretty close, they mean between 100 and 50 parsecs, or between 326 and 163 light years away. This was roughly between the transition between the Pliocene Epoch and the last major 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 explains.

"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." he added.

This is also supported by large-scale carbon deposits in soils that correlate with time. 

"The observation is that there's a lot more charcoal and soot in the world starting a few million years ago," explained Melott.

"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 increase in fires is thought to have stimulated the transition from woodland to savanna in a lot of places -- where you had forests, now you had mostly open grassland with shrubby things here and there. 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," he concluded.

The original paper is published in the Journal of Geology on the 3rd of March 2019.