Did supernovae contribute to evolution? A new study links humans who walk upright to the explosion of stars millions of years ago.
Humans and our primate relatives differ in many ways, but the fact that we walk on two legs is one of the most obvious. Precisely how our ancestors evolved that distinctive trait is a much debated mystery. Now a new theory is on the table: What if one of the contributing factors were stellar explosions?
Supernovae
According to the new hypothesis published inThe Journal of Geology, a supernova, the explosion of a star at the end of its life, could have bathed the Earth with cosmic radiation,beginning about 8 million years ago and peaking at about 2.6 million years ago.
This radiation would have ionized the lower atmosphere, which would probably cause an increase of the rays towards the earth. This, in turn, could have increased forest fires, eradicating the forests of Africa, where the first humans are believed to have originated, and allowing the savannah to take their place.Our ancestors should have abandoned the trees and embraced the savannah.Bipedal locomotion would have provided a number of advantages, since height increases visibility.
“It is thought that there was already a tendency for hominids to walk on two legs, even before this event,” said astronomer and physicist Adrian Melott of the University of Kansas (USA). “Butmainly adapted for climbing trees. After this conversion to the savannah, they would have to walk much more often from tree to tree through grasslands, sothey became better able to walk upright.They could see over the grass and watch for predators. This conversion to the savannah is believed to have contributed to bipedalism as it became more and more dominant in human ancestors, “Melott clarifies.
A little history
A few years ago, astronomers revealed that they had founda layer of iron isotopes 60on ancient sea beds, an isotope with no known natural mechanisms of terrestrial production, which means it had to come from space. And because it has a known half-life, it can be accurately dated.
These isotopes were tracked in two events, the first 6.5 to 8.7 million years ago and the second 1.7 to 3.2 million years ago, within 300 to 163 light years of Earth.
Based on this information revealed by iron-60 isotopes, Melott’s team has extrapolated what would have happened on Earth during these bombings. “We calculated the ionization of the atmosphere from cosmic rays that would come from a supernova as far away as the iron-60 deposits indicate,” the expert clarifies.
“It seems this was the closest in a much longer series.We argue that it would increase the ionization of the lower atmosphere by 50 times. Generally, you don’t get ionization of the lower atmosphere because cosmic rays don’t penetrate it, but the most energetic rays from supernovae come directly to the surface, “continues Melott.
Ionization occurs when atoms or molecules become charged by gaining or losing electrons.In this case, the cosmic rays would have thrown out a lot of loose electrons. In turn, the electrons help transport the rays from the clouds to the ground, so these loose electrons would have made it easier for the rays to access.
What is the connection?
And how does this connect to wildfires? There are a large number of carbon deposits on the ground that correspond to the bombardment period of the supernova.
“The observation is that there is much more carbon and soot in the world from a few million years ago,” Melott said. “It’s everywhere, and no one has any explanation as to why it would have happened around the world in different climate zones. This could be an explanation.”
It is not likely to be the only explanation; Evolution is, after all, a fairly complex phenomenon, but these researchers’ argument certainly makes an interesting connection between the cosmos and our ancestors.
Melott stated that a similar event is not likely to occur in our near future. The closest star capable of exploding in a supernova in the next million years is Betelgeuse, which is about 200 parsecs (652 light years) away from Earth.
“Betelgeuse is too far away to have effects as strong as these, so there is no need to worry about this. Let us worry about solar proton events. That is the danger that haunts us with our technology: a solar flare that will leave us without power. Imagine months without electricity, “says Melott.
Referencia: From Cosmic Explosions to Terrestrial Fires? The Journal of Geology 2019. Adrian L. Melott, and Brian C. Thomas. arXiv:1903.01501 [astro-ph.EP] (or arXiv:1903.01501v1 [astro-ph.EP] for this version ) DOI: 10.1086/703418
