A team of researchers led by Walter Robert Binns of Washington University in St. Louis has detected traces of 60Fe in cosmic rays flying through space, revealing that ashes from a nearby supernova continue to rain down on Earth up to this day.
According to the study published in the journal Science, 60Fe or Iron-60 is a radioactive isotope in cosmic rays that is believe to be produced by core-collapsed supernovas marking the explosive deaths of giant stars at least 10 times the mass of the sun.
60Fe has a half-life of 2.6 million years. This short half-life implies that the traces detected by the Cosmic Ray Isotope Spectrometer (CRIS) aboard NASA's Advanced Composition Explorer (ACE) must have been produced in the last million years. 60Fe cosmic rays are believed to be evidence of at least two separate supernova events. The first event synthesizes the isotopes while the second supernova makes them accelerate to extreme velocities.
Researchers suggest that the Iron-60 they detected came from supernovae that marked the death of massive stars in the nearby Scorpius-Centaurus association within 2,000 light years or so of Earth.
Previous studies from other researchers also reported the discovery of 60Fe in moon rocks brought to Earth by Apollo astronauts and in the deep-sea rocks of Earth.
The high level of 60Fe found in deep-sea rocks implies that debris from supernova had been raining on the earth since way back in the past, possibly affecting evolution. Radiation from these kinds of explosions have the ability to cause extreme changes in climate. Nearby Supernovae can also affect evolution by spraying radioactive material in the Earth.
"It might be possible that an increased rate of mutations directly influenced evolution - for example, increase in brain size," said Dieter Breitschwerdt, an astrophysicist at the Berlin Institute of Technology, in Space.com.