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While human ancestors went from swinging in trees to walking on two legs, they may have received momentum from an unexpected source: old supernovas.
These mighty stellar explosions may have fed the Earth with enough energy to change its climate, bathing the Earth into electrons and generating powerful storms filled with lightning, according to a new hypothesis.
The lightning would then have been able to ignite wild fires that burned African landscapes. As the savannah replaced the forest habitat, the first humans who lived there may have been pushed to walk on two legs, according to the new study. [Top 10 Mysteries of the First Humans]
However, do not go too quickly to conclusions. Many factors have probably contributed to the evolution of bipedalism, a process that began several million years before these stellar explosions, said an expert at Live Science.
Clues about the old supernovas have been found in traces of iron 60 in the earth's crust. This radioactive isotope, or version of iron, originates from the stars near the end of their life; It is thought that scientists wrote in the new study: they would have arrived on Earth after the violent explosion of supernovae in our cosmic district millions of years ago.
Previous studies have described traces of iron 60 conserved on Earth from stars that exploded about 8 million years ago. This explosive activity culminated with a supernova (or series of supernovae) that occurred about 123 light-years from Earth about 2.6 million years ago, scientists said. Around this time, at the dawn of the Pleistocene epoch, the forests of East Africa began to give way to open grasslands.
The high-energy emissions of supernovas may have been strong enough to penetrate the troposphere, ionize the Earth's atmosphere and affect the planet's climate, told Mel Melvin, lead author of the study. , Adrian Melott. Science.
The researchers estimated that the energy infusion of the supernovae could have multiplied by 50 the rate of atmospheric ionization; This would have greatly increased the risk of cloud-to-ground flash, which could have triggered more wildfires, Melott said.
While scientists could not accurately calculate the number of additional lightning events that would result from a 50-fold increase in ionization, "the potential exists for a significant increase," they write in the study.
Today, most forest fires are caused by human actions. previously, "lightning was the leading cause of forest fires," Melott explained. Forests burned by forest fires give way to grasslands; More open savanna meant more walking from tree to tree, which would exert evolutionary pressure on human kinship so that it spends more time on two legs.
Still, hominines were already becoming walkers long before the start of the supernova's activity, William Harcourt-Smith, an assistant professor of paleoanthropology at Lehman College of City University in New York, told Live Science.
The first evidence of bipedalism in ancient humans goes back about 7 million years and the transition to a full biped was well underway about 4.4 million years ago, said Harcourt-Smith, who did not participate in the study.
"There are 3.6 million years, we had competent bipeds, like" Lucy ", and there are 1.6 million years, [we have] to make bipeds very similar to us, "he explained.
Bipedalism is energy efficient, frees hands for transport, and provides better visibility for predators or distant resources. The move to the right march "certainly concerns the opening of grassland habitats and adaptation to this type of environment," Harcourt-Smith said. However, the study does not provide compelling geological evidence of forest fires as being the main cause of these dramatic changes in ancient habitats of Africa, he said.
In addition, the destructive power and magnitude of these hypothetical forest fires are based on a significant increase in lightning due to supernovas, a variable that the researchers "could not estimate," they wrote in a report. l & # 39; study.
The results were published online today (May 28) in The Journal of Geology.
Originally published on Science live.
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