Supernova linked to human bipedalism

According to a paper authored by US physicists, an exploding star between 326 and 163 light years away bombarded Earth with cosmic energy, increasing ionisation in our planet’s lower atmosphere 50-fold.

Ionisation describes an atom or a molecule acquiring a negative or positive charge by gaining or losing electrons. It’s a way of radiation transferring its energy to matter.

This radiation, the effects of which peaked on Earth around 2.6 million years ago, triggered cloud-to-ground lightning strikes that ignited forest fires. The resulting transition from forests to open grassland forced our ancestors to walk upright between trees.

Adrian Melott, lead author and professor at the University of Kansas, said: “It is thought there was already some tendency for hominins to walk on two legs, even before this event.

“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. They could see over the tops of grass and watch for predators.”

The authors have based their theory on a layer of iron-60 deposits in the world’s seabeds – a radioactive isotope produced at the centre of large stars.

“The observation is that there’s a lot more charcoal and soot in the world starting a few million years ago,” Melott said. “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.”

It takes a monumental cosmic event such as an exploding star to penetrate Earth’s atmosphere and cause lower-atmosphere ionisation. The next star capable of exploding into a supernova in the next million years is Betelgeuse, which is around 652 light years from Earth — too far away to have an effect on us.

The study has been published in the Journal of Geology.