Wildfires triggered by lightning from the aftereffects of a series of nearby ancient supernovae may have caused proto-humans to walk on two feet, say researchers. The idea is that these Hominins would have been driven from torched forests and forced to adapt to newly-created Northeast African savannas.
A paper appearing the Journal of Geology makes the case that supernovae bombarded Earth with cosmic rays starting as many as 8 million years ago ; with a peak some 2.6 million years ago. This, in turn, would have caused a virtual avalanche of electrons in the lower atmosphere that would have set off a chain of events that caused global wildfires. As a result, our earliest ancestors may have been permanently forced from the trees and into the surrounding savannas of Northeastern Africa.
There are several smoking guns which the researchers use to support their thesis. Arguably, the most important is a telltale layer of supernovae-linked Iron-60 deposits that line the world’s sea beds as well as carbon deposits found in soils that match the timing of these events. Based on these deposits, the University of Kansas says that astronomers have high confidence that a series of supernovae exploded in earth’s immediate cosmic neighborhood at the closest distance of only 163 light years.
Cosmic rays from this series of supernovae events caused atoms in the atmosphere to be ionized or stripped of their electrons . This created an abnormal atmospheric proliferation of free electrons that in turn led to a buildup of cloud voltage. The was coupled with a cascade of electrons down deep into the atmosphere which in turn led to an unusual number of lightning bolts. And lightning strikes are the most common natural cause of forest and/or ground fires.
This new work builds on observations of increased instances of terrestrial fire outbreaks over the last few million years, Adrian Melott, the paper’s lead author and a professor emeritus of physics and astronomy at the University of Kansas in Lawrence, told me. But he says more research on how lightning is actually initiated in earth’s atmosphere and its connection with cosmic rays would be helpful.
The most surprising aspect is that a supernova may have contributed to human evolution, Brian Thomas, the paper’s co-author and a physicist at Washburn University in Topeka, Kansas, told me. Scientifically, he says, we may have an explanation for the increase in fires and changes in vegetation around the time of the supernovae.
Researchers already know that supernovae ejecta played a large role in providing the cosmos’ heavy building blocks of life as we know it. But what’s fascinating is that now such work indicates just how wide-ranging supernovae’s influence may have been — from seeding the cosmos with the material of which rocky planets are made to spurring our own ancestors to become fully bipedal.
The researchers estimate that this series of supernovae, likely responsible for carving out a large gaseous cavity in the local interstellar medium, now known as the Local Bubble, would have also created a large magnetic field. This magnetic field, in turn, would have reflected the supernovae’s flux of high-energy cosmic rays back into the walls of this cavity and extended the time our atmosphere would have been irradiated by such high-energy particles. From there, the resulting lightning and the wildfires, the carbon and the soot, turned into deposits that researchers are able to detect today.
Is Earth in danger of such supernovae events today?
The supergiant star Betelgeuse, located in the Western shoulder of the Orion constellation, could go supernova in the next million years. But because it’s more than 650 light years distant, it’s likely to have little effect on Earth.
But such research still gives pause to wonder if the development of life in the nearby cosmos is also linked to such cosmic serendipity? And did other supernovae cause follow-on effects that also vectored life toward bipedalism on other Earthlike planets?