Supernova evidence found in ice cores

A supernova that exploded about 2.6 million years ago, located 150 to 163 light-years from Earth, may have affected Earth's environment and early human evolution, according to recent studies. Scientists discovered traces of iron-60, a rare radioactive isotope, in Antarctic ice cores, indicating the event's impact on Earth.

Iron-60's origin and half-life

Iron-60 has a half-life of 2.6 million years, so any found on Earth today must have come from an external source, such as a supernova. This discovery supports the idea that the supernova occurred in the distant past and left a detectable mark on Earth's environment.

Fluctuations in interstellar dust

A 2019 study in Physical Review Letters found varying levels of iron-60 in ice cores from 40,000 to 81,000 years ago, suggesting changes in the density of interstellar dust over time. The study noted that the amount of iron-60 reaching Earth in that period was less than what is observed today.

Increased atmospheric ionization

Astrophysicist Adrian Melott suggested that a supernova at 163 light-years from Earth would have significantly increased atmospheric ionization, potentially by 50 times. This could have led to more frequent and intense lightning strikes, increasing the likelihood of wildfires in dry and wooded areas.

Environmental changes and bipedalism

Melott and Brian Thomas proposed that the increase in lightning and fires could have transformed African forests into savannas. This environmental shift may have favored the development of bipedalism, as walking upright would have been more advantageous in open environments.

Bipedalism predates the event

However, some researchers argue that bipedalism was already established in early human ancestors around 4.4 million years ago, long before the supernova event. While the cosmic event may have influenced existing trends, it may not have been the primary driver of bipedalism.

Cosmic rays and biological effects

Caitlyn Nojiri's research suggested that cosmic rays from the supernova could have caused a significant mutagenic effect on living organisms at the time, adding a biological dimension to the impact of the event. This could have influenced genetic changes in early humans.

Earth's galactic position

Researchers note that Earth's position in the galaxy, within a vast void created by stellar explosions, may place it in a region where such cosmic events are more common. The peak of iron-60 observed between 2 and 3 million years ago is attributed to a supernova from the Upper Centaurus Lupus or Tucana Horologium associations.

Interdisciplinary research insights

The convergence of nuclear physics, geology, astrophysics, and paleoanthropology in this research highlights how Earth's environment and evolution may be more influenced by its galactic surroundings than previously thought. This interdisciplinary approach offers new perspectives on the interplay between cosmic events and life on Earth.