According to a recent study, ancient supernovas might have been the reason humans shifted from swinging by trees to walking on legs. These immensely powerful explosions created a change in the climate of the planet with its huge energy. It charged the atmosphere of Earth with electrons and caused frequent lightning and storms. The study has been published in the Journal of Geology.
The lightning, storms could have caused wildfires which damaged entire landscapes in Africa. The study suggests that as the forests were replaced by savanna, early humans who resided may have been forced to walk on two legs. However, it would not be wise to draw quick conclusions. Several factors have contributed to bipedalism, which began several million years before the stellar explosions occurred.
Traces of iron-60 found in the Earth’s crust contained clues to the supernova. This radioactive isotope of iron is found in the stars which are approaching their end. Previous studies show that the trace of iron-60 on Earth came from the explosion of stars approximately 8 million years before. The explosions peaked with the supernova that took place 123 light years away from Earth, 2.6 million years ago.
Adrian Melott, principal author of the study and Professor of Astronomy at the University of Kansas commented that the very high energy emissions of the supernova could have penetrated the troposphere thus ionizing the atmosphere of Earth. This caused drastic changes in the Earth’s climate.
Scientists estimated that the infusion of energy from supernova increased the atmospheric ionization by 50, which highly increased the cloud-to-ground lightning leading to more violent wildfires. Although they could not precisely calculate the exact increase in the lightning events from the 50 fold boost of atmospheric ionization, the potential for increase is very high.
Most wildfires today are a result of human actions, but previously the principal factor of wildfires was lightning. Scorching of forests by wildfires led to grasslands, and the open savannas meant more walking which would create more pressure on humans to spend increased time on legs.
William Harcourt-Smith, professor of paleoanthropology at Lehman College said that long before the peak of supernovas, hominins were becoming upright walkers. The very first proof of bipedalism in human beings was seen almost 7 million years ago, and the switch to full bipedalism happened almost 4.4 million years ago.
Bipedalism is energy efficient, as a result of which hands can be used for carrying necessary items. Grassland habitats support for full upright walking however it is not fully certain that the wildfires are the main reason behind these changes.