Exploding supernova infernos forced humans to stand on two feet

AN ANCIENT barrage of exploding stars close to Earth is the reason humans learnt to walk on two feet rather than all fours, according to research.

Scientists believe the intense period of supernovae, which peaked approximately 2.6million years ago, caused a surge in lightning strikes which incinerated much of the heavily forested Earth.

Early humans then had to adapt from living in and around trees to surviving in open savannas, meaning the ability to cross exposed grassland at speed and spot predators above the vegetation became crucial.

A supernova takes place when certain types of star come to the end of their life. They can briefly outshine entire galaxies and radiate more energy than the Sun will in its entire lifetime.

Experts at the University of Kansas found clues to the heavy period of supernova activity around the turn of the Pliocene Epoch and ice age at the bottom of the sea.

A “telltale” layer of iron-60 deposits, referring to a type of isotope, pointed to an ionisation of the atmosphere from cosmic rays.

The bottom mile of the atmosphere is never usually affected in this way, apart from when blasted with energy from exploding stars.

Writing in the Journal of Geology, the scientists say this 50-fold increase in cosmic energy enabled a surge in cloud-to-surface lightning bolts that turned forests into infernos.

Prof Adrian Melott, who led the research, said: “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.

“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.”