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Exploding stars have mankind on two feet

Stars that end their lives in gigantic explosions, called supernovae violently spewing out elements and debris into space. Credit: NASA/CXC/SAO

If human ancestors went from swinging through the trees to walking on two legs, they can received a boost from an unlikely source: ancient supernovas.

These powerful stellar explosions may have showered the Earth with enough energy to shift the planet, the climate, bathing the Earth in electrons and sparks powerful, lightning-filled storms, according to a new hypothesis.

Lightning could have ignited raging fires that scorched African landscapes. If savanna replaced forest habitat, the early people who lived there, can be pushed to walk on two legs, the new study suggests. [Top 10 Mysteries of the First Humans]

However, don’t go jumping to conclusions just yet. Of the many factors that have contributed to the evolution of bipedalism, a process that began many millions of years before these stellar explosions took place, an expert told Live Science.

Instructions for the old supernovas were found in the traces of iron-60 in the earth’s crust. This radioactive isotope, or the version of iron, has its origin in the stars almost at the end of their life; it is thought to have arrived on the Earth after the violent explosions of supernova in our cosmic neighborhood of millions of years ago, scientists wrote in the new study.

Previous studies described the traces of iron-60 is saved on the Earth from stars that blew up, beginning around 8 million years ago. That explosive activity peaked with a supernova (or a series from the supernova) located about 123 light-years away from the Earth about 2.6 million years ago, the scientists reported. Around that time, the beginning of the Pleistocene era, the forests in eastern Africa began to give way to the open grasslands.

High-energy emission from the supernova’s are strong enough to penetrate into the troposphere, ionizing the atmosphere of the Earth and the influence of the planet again, lead study author Adrian Melott, professor emeritus at the Department of Physics and Astronomy at the University of Kansas, told Science.

The researchers estimate that the energy infusions from the supernova may have increased atmospheric ionization by a factor of 50; this would be greatly increased and the probability of a cloud to ground lightning, which, in turn, would have sparked more fires, Melott said.

While the scientists could not exactly calculate how much additional lightning events would be the result of a 50-fold increase in ionization, “the potential is there for a large increase,” they wrote in the study.

Today, most forest fires are caused by human actions; therefore, “lightning was the major cause of the forest fires,” Melott explains. Forests burned by wildfires would give to grasslands; open savannah meant more to walk from tree to tree, which would then evolutionary pressure on the human family members to spend more time on two legs.

Yet, hominins were all still upright walkers long before the supernova activity peak, William Harcourt-Smith, an assistant professor of paleoanthropology, with Lehman College of The City University of New York, told Science in an e-mail.

The first evidence for bipedalism in the the old woman dates to about 7 million years ago, and the transition to bipedalism was well underway with approximately 4.4 million years ago, said Harcourt-Smith, who was not involved in the study.

“By 3.6 million years ago, we have committed bipeds, like ‘Lucy’, and by 1.6 million years ago, [we have] obligatory bipeds, very similar to us,” he explained.

Bipedalism was more energy-efficient, freed up the hands for carrying, and offered better visibility of distant predators or sources. The shift to fully walk upright “especially with regards to the opening up of the grassland habitats and to adapt to this environment,” Harcourt-Smith said. But the study does not provide compelling geological evidence of forest fires as the main cause for the dramatic changes in Africa the old habitats, ” he said.

What’s more, the destructive power and the scope of that hypothetical fires hinges on a significant increase of lightning as a result of the supernova, a variable that the researchers were “unable to estimate,” they wrote in the study.

The findings are published online today (May 28) in The Journal of Geology.

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Originally published on Live Science.

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