Lightning strikes may have got humans to stand on their two legs, says S.Ananthanarayanan.
Animals approach human ability in many fields to greater or lesser degrees. There is no mammal, however, that gets off its four feet and stands upright most of the time. Bipedalism, with its advantages, at the cost of undoubted stability of the four-legged stance, appears to be a purely human adaptation.
Adrian L. Melott, and Brian C. Thomas, from the Departments of Physics and Astronomy, University of Kansas, and Washburn University, Topeka, Kansas, write in the Journal of Geology, of the University of Chicago, that the change of humans from movement on four legs to two legs could be connected with cosmic events that affected the earth’s ecosystem.
While the early humans, like chimpanzees and baboons, had a tendency to walk on two legs, the facility was mainly one of freely moving through trees and not a form for moving over the ground. It is considered that proper bipedalism arose when hominids, or proto-humans, needed to move distances between trees or benefited by being above the grassland, to better spot predators. The authors of the paper suggest that radiation from cosmic supernova activity, between eight and 2.6 million years ago, which led to an electrically charged atmosphere and forest fires, particularly in northeast Africa, and replaced tropical forests with grassland, may have played a role.
A supernova, as the name suggests, is an energetic ‘new’ star, a stage in the formation of stars. Stars are believed to form when a huge cloud, mainly of hydrogen, the simplest of the elements, collapses into itself due to gravity. High pressure and temperature is generated, which brings about the ‘fusion’ of the nuclei of hydrogen atoms, to form nuclei of helium. The formation of helium, which is the same process that powers the hydrogen bomb, releases huge energy. This leads to further fusion events and a chain reaction results in explosive expansion. The expansion, which leads to cooling, continues until it is reined in by the forces of gravity, and compression sets in again. The compression lasts until there is fusion of helium nuclei, to even heavier elements, with release of energy, and the cycle goes on until all the elements, up to the element, nickel, are created. While the fusion of nuclei of lighter elements, until nickel, can release energy that is sufficient to sustain fusion, this is not true for the nucleogenesis of heavier elements, for which net external inputs of energy are needed.
While these higher elements are created during the last stages of some supernovae, a marker of a supernova explosion is a form of the element iron, with 60 particles (26 protons and 34 neutrons) in the nucleus, in place of the usual 56 (26 protons and 30 neutrons). This form of iron, called Fe-60, however, is radioactive and decays to cobalt, as Co-60, which, in turn, decays to nickel, Ni-60. As any Fe-60 that the earth started out with would hence have decayed and no longer be there, if we still find traces of Fe-60, this would be evidence of recent supernova activity. The depth at which these traces are found would then indicate the timing of the supernovae events.
An effect of supernova activity would be massive increase in the cosmic ray onslaught that strikes the earth. One effect of cosmic rays is to destroy the ozone layer and increase the UV radiation that comes down to the surface. Another is to raise the level of ionization in the atmosphere and increase the electrical activity in the atmosphere, which would have its effects on planetary ecology.
Surveys using boreholes in the seabed do indicate the presence of Fe-60 that reveals supernova activity, from eight to 2.6 million years ago. So far, this activity has been linked with the onset of the ice ages and the extinction of the dinosaurs. The authors of the paper refer to the available Fe-60 record have taken it that the most recent supernovae, about 2.6 million years ago, the beginning of the Ice Age, is representative of the series and was about 163 light years away. They have then worked it out that the level of radiation would have caused a 50-fold increase in the level of ionization of the atmosphere.
The paper says that it had been proposed that increased cosmic ray activity generates avalanches of electrons in the atmosphere, which are the main initiator of lightning. While this proposal was an ‘eminently reasonable idea’, the paper says, recent work with low lying clouds above mountains in Armenia has revealed a number of instances where electron avalanches of less than a microsecond ended as nearby lightning flashes. This is direct evidence, the paper says, to turn the proposal into a compelling theory.
A 50-fold increase in ionization would thus lead to substantial, if not equal, increase in lightning strikes, rise in levels of nitrates and drop in CO2. The drop in CO2 would lead to cooling, which has been observed at the start of the epoch. However, basic to the effects is the “large increase in the lightning frequency,” the paper says.
Lightning, even now, the paper says, is the main natural initiator of wildfires. The increase, approaching 50-fold, of lightning would thus have devastated forests, and this, the paper suggests, was the beginning of the change in the nature of the vegetative cover, worldwide. There is evidence of wildfires that followed major impact events (asteroid hits), in the form of soot and carbon related sediments. This has been found to be the case, the paper says, since about 7 million years ago, to suggest high incidence of wildfires during the period.
The finding supports the belief, the paper says, that it was change in the form of tree cover that provided the evolutionary selector and the rise of bipedalism. Supernova events in the vicinity of the earth, hence, may be the reason that humans became bipeds, and thrived in the changed environment, multiplied, migrated from northeast Africa to the rest of the world, and all else!
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