An ancient barrage of exploding stars close to Earth is the main reason early humans learnt to walk on two feet rather than all fours, according to new research.

Scientists believe the intense period of supernovae, which peaked approximately 2.6 million 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 supernovae activity around the turn of the Pliocene Epoch and ice age at the bottom of the sea.

A “telltale” layer of iron-60 despots, referring to a type of isotope, pointed to an ionization 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.