A supernova is a brief, final stage event that happens to a massive star. It ends with an epic explosion of its stellar content. When happening close enough to Earth, it could be observed with our naked eyes. However, a recent study suggested that ancient supernovae occurence might have been more than just blips of fireworks to human ancestors--they might have prompted the hominins to walk on their feet.
The rise of bipedalism is considered a crucial part of human evolution. Fossil evidence revealed that between three and four million years ago, our ancestors started to stand on feet, which freed up their hands for other tasks, such as collecting food, making tools, and even starting a fire.
Anthropologists cannot settle on whether we got smart (by growing a bigger brain) before we stood up, or the other way around. But one thing is for sure, the change of locomotion was associated with a change of landscape, meaning the places where the hominins dwelled, mainly northeastern Africa, suddenly had fewer trees but more grass and shrubs.
Scientists have long suspected that frequent lightning and fire might have been the culprits behind the thinning of the forests. The connection between lightning and supernovae, although quite obscure, has previously been proven.
A dying star can be as far as a couple of thousand lightyears away, but its explosion-caused intense gamma radiation can spread across a big region of the galaxy. As the waves of high-energy photons bombard the atoms in Earth's upper atmosphere, they knock the electrons out of their shells and set off electron cascades, which results in intense, frequent lightning. By looking inside the ice-core extracted from the Antarctica, geologists found elevated levels of nitrate ions (nitrogen oxide is a chemical product of lightning), which coincided with the supernovae dated back to 1006 and 1054.
For the recent study by Adrian Melott and Brian Thomas, astronomers from the University of Kansas and Washburn University, the duo built their argument on the previous and current measurement of iron-60, a trace metal can be traced back to the nucleosynthesis process within supernovae, in the seafloor. They discovered that within the deep-sea crust there is an enrichment of iron-60 all over the world, coinciding with the geological time between the Pliocene Epoch and the Ice Age. Their calculation also confirmed that the ancient celestial explosions could have happened as close as 163 light years away, which made the lighning-caused wildfire more likely.
This latest discovery is published in the Journal of Geology.
Are you interested in learning more about the evolution of human bipedalism? Explore a part of our history in the following video from PBS Eons.
When We First Walked (PBS Eons)