Massive supernovas may have influenced human evolution

Researchers are investigating the possibility that an ancient supernova induced proto-humans to begin walking on two legs.

Supernovae bombarded Earth with cosmic energy starting as many as 8 million years ago — with a peak roughly 2.6 million years ago. This bombardment initiated an avalanche of electrons in the lower atmosphere setting off a chain of events that could have feasibly ended with bipedal hominins such as homo habilis — appropriately dubbed “handyman” because of its tendency to use tools — beginning to walk upright.

That is the case put forward in a new paper published in the Journal of Geology.

One of homo habilis’ key skills to survive was the ability to craft and use tools — could the adaption to use hands have resulted from circumstances created by supernovas?

The authors believe atmospheric ionization probably triggered an enormous upsurge in cloud-to-ground lightning strikes that ignited forest fires around the globe. These infernos could be one reason ancestors of homo sapiens developed bipedalism — to adapt in savannas that replaced torched forests in northeast Africa.

Adrian Melott, professor emeritus of physics & astronomy at the University of Kansas and the paper’s lead author, says: “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.”

Melott believes that after this conversion to savanna, our ancestors would have had to walk from one tree to another across the grassland far more frequently — in turn, becoming better at walking upright.

He continues: “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.”

Infernos destroying foliage may have forced our ancestors to walk upright for longer periods

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 — between 100 and only 50 parsecs or 163 light years away — during the transition from the Pliocene Epoch to the Ice Age.

Melott continues: “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.

“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.”

Melott and his co-author Brian Thomas of Washburn University suspect that ionization in the lower atmosphere meant an abundance of electrons would form more pathways for lightning strikes.

Melott says: “The bottom mile or so of the atmosphere gets affected in ways it normally never does.

“When high-energy cosmic rays hit atoms and molecules in the atmosphere, they knock electrons out of them — so these electrons are running around loose instead of being bound to atoms.”

Ordinarily, in the lightning process, there’s a buildup of voltage between clouds or the clouds and the ground — but, current can’t flow there aren’t enough electrons are around to carry it. So, it has to build up high voltage before electrons start moving.

Melott explains further: “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.”

The KU researcher said the probability that this lightning spike touched off a worldwide upsurge in wildfires is supported by the discovery of carbon deposits found in soils that correspond with the timing of the cosmic-ray bombardment.

The team notes that are greater amounts of charcoal and soot in the geological record starting a few million years ago.

Melott says: “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.”

Melott said no such event is likely to occur again anytime soon. The nearest star capable of exploding into a supernova in the next million years is Betelgeuse, some 652 light years from Earth.

Melott concludes: “Betelgeuse is too far away to have effects anywhere near this strong.



“So, don’t worry about this. Worry about solar proton events. That’s the danger for us with our technology — a solar flare that knocks out electrical power. Just imagine, months without electricity.”

Original research: http://dx.doi.org/10.1086/703418