An international team of scientists has found evidence of a series of massive supernova explosions near our solar system, which showered the Earth with radioactive debris.
The scientists found radioactive iron-60 in sediment and crust samples taken from the Pacific, Atlantic and Indian Oceans.
The iron-60 was concentrated in a period between 3.2 and 1.7 million years ago, which is relatively recent in astronomical terms, said research leader Dr Anton Wallner a nuclear physicist in the ANU Research School of Physics and Engineering.
"We were very surprised that there was debris clearly spread across 1.5 million years," said Dr Wallner. "It suggests there were a series of supernovae, one after another.
"It's an interesting coincidence that they correspond with when the Earth cooled and moved from the Pliocene into the Pleistocene period."
The team from Australia, the University of Vienna in Austria, Hebrew University in Israel, Shimizu Corporation and University of Tokyo, Nihon University and University of Tsukuba in Japan, Senckenberg Collections of Natural History Dresden and Helmholtz-Zentrum Dresden-Rossendorf (HZDR) in Germany, also found evidence of iron-60 from an older supernova around eight million years ago, coinciding with global faunal changes in the late Miocene.
Some theories suggest cosmic rays from the supernovae could have increased cloud cover.
A supernova is a massive explosion of a star as it runs out of fuel and collapses.
The scientists believe the supernovae in this case were less than 300 light years away, close enough to be visible during the day and comparable to the brightness of the Moon.
ContactDr Anton Wallner