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Humans and our primate relatives differ in many ways, but the fact that we walk on two legs is one of the most obvious. It is precisely how our ancestors developed this trait is a well-debated mystery. Now, there is a new idea. And if one of the contributing factors was the giant explosion in the sky?
It's not as crazy as it sounds. According to a hypothesis expounded by astronomers in a new article, the exploding stars at the end of life – the supernovae – could have bathed the Earth with cosmic radiation, about 8 million years ago and culminating there are about 2.6 million years.
This radiation would have ionized the lower atmosphere, which would have probably led to an increase in the number of lightning strikes between clouds and soil. This, in turn, could have increased forest fires – eradicating the forests of Africa, from which the first human beings would originate, and allow the savannah to take their place.
You see, bipedal locomotion confers a number of benefits to the human species, especially in the African savannah where height increases visibility.
"It is thought that hominines already tended to walk on two legs even before this event," said astronomer and physicist Adrian Melott of the University of Kansas.
"But they were mainly adapted to climb trees, and after this conversion to savannah, they would be much more likely to walk from one tree to another across the meadow, and they would become better at walking. standing.
"They could see above the herbs and watch the predators – it is thought that this conversion to the savanna contributed to bipedalism as it became more and more dominant among human ancestors."
As you can see, there is still a lot of guesswork and connections between the points from the supernovae to the savannah. But Melott and his team brought receipts.
A few years ago, astronomers revealed that they had discovered a layer of iron isotopes 60 in the old seabed, isotope devoid of any known terrestrial production mechanism, which means that "no" is not known. it had to come from space. And since it has a known half-life, it can be dated accurately.
These isotopes were attributed to two events, the first there are 6.5 to 8.7 million years ago and the second there are 1.7 to 3.2 million years ago, between 300 and 163 light-years from Earth.
Based on this information revealed by iron isotopes 60, the Melott team extrapolated what would have happened on Earth during these bombings.
"We have calculated the ionization of the atmosphere by the cosmic rays that would come from a supernova about as far as the iron-60 deposits indicate," he said. he declares.
"It seems like it's the closest in a much longer series.We think it would increase 50-fold the ionization of the lower atmosphere.In general, ionization in the lower atmosphere n & # 39; It is not obtained because the cosmic rays do not penetrate far, but the most energetic supernovae descend to the surface. "
Ionization occurs when atoms or molecules charge by gaining or losing electrons. In this case, the cosmic rays would have lost a packet of electrons. In turn, the electrons help transport the lightning from the clouds to the ground, so these loose electrons would have made lightning easier.
So, how does this connect to forest fires? There are a lot of blackened carbon deposits in the ground that correspond to this bombardment period.
"The finding is that there is a lot more charcoal and soot in the world from a few million years ago," Melott said. "It's everywhere and nobody can explain why it would have happened anywhere in the world, in different climate zones." This could be an explanation.
This is probably not the only explanation – evolution is, after all, a rather complex phenomenon – but the team's argument establishes an interesting link between the cosmos and our ancestors.
The research was published in the Journal of Geology.
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