Supernovae May Have Prompted Human Ancestors to Walk Upright

The remnant of a supernova. (X-ray: NASA / CXC / Rutgers / J.Hughes; Optical: NASA / STScI)

(CN) – Research published Tuesday raises questions about mankind’s cosmic origins. Not an attempt to credit ancient aliens, but instead an elegant examination of how cosmic rays from dying stars may have set off a chain of terrestrial events to create the conditions for our ancient ancestors to walk upright.

“It is possible that nearby supernovae played a role in the evolution of humans. This should be borne in mind as more research is done, particularly in the initiation of lightning,” wrote physicists Adrian Melott and Brian Thomas in their paper “From cosmic explosions to terrestrial fires?” They published their work Tuesday in The Journal of Geology.

Several million years ago, our ancestors were driven onto two feet in order to survive the savannas of northeast Africa after massive wildfires turned ancient forests into grassy plans. Researchers from the physics and astronomy departments at the University of Kansas and Washburn University in Topeka built a model testing the impact of cosmic rays from dying stars on terrestrial lightning storms – the leading cause of wildfires before humans came along.

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

Starting around 8 million years ago, evidence suggests chains of supernovae exploded throughout the Milky Way. The supernovae peaked around 2.6 million years ago, lining up with the Pliocene-Pleistocene transition when hominids likely started walking on two feet – the pivotal step that set humanity off on an extraordinary evolutionary path eventually leading it to study its own origins.

Cosmic rays can increase ionization in the atmosphere causing positive ions and electrons in the air to separate. These freed electrons are great conductors of electricity, making paths between clouds or to the ground. Enough ionization can set off what researchers describe as the “electron avalanches” causing lightning.

Researchers believe supernovae exploded within 163 light years of Earth near the Ice Age transition based on iron-60 deposits found lining sea beds around the world. Iron-60 is produced in large stars and has a half-life of 2.6 million years, providing an accurate way of measuring time.

The model focuses on radiation from common type IIP supernovae 50 parsecs from Earth and assumes the Local Bubble of hot gas had developed. In addition to looking at muons – elementary particles which can hit the ocean down to a kilometer – researchers considered “additional substantial effects which could also indirectly have had a major effect on the biota, including the evolution of our species.”

“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 said. As a result, “there would be a lot more lightning bolts.”

While the authors note the ancient hominins may have been bipedal in some limited fashion to go from tree to tree in the once dense forests of Africa, when the forests became savannas they would have been forced to walk through the grassland to find trees – and gotten better at walking upright in the process.

Cosmic rays constantly pelt the Earth, but most are blocked out by the planet’s magnetic field and atmosphere. Previous research focused on how astrophysical ionizing radiation produced by supernova contributed to mass extinction events. But as Melott and Thomas show, many more interesting things must happen in between – after all, when it isn’t dying off, life on Earth flourishes.

%d bloggers like this: