Supernovae showered Earth with radioactive debris

Hebrew University scientists take part in international research project.

Earth (photo credit: NASA)
(photo credit: NASA)
An international team of scientists, including researchers from the Hebrew University of Jerusalem, has detected a series of massive supernova explosions that occurred two to three million years ago and showered the Earth with debris of the radioactive isotope iron-60.
A supernova is an explosion of a star that collapses as it runs out of nuclear fuel. In the process, it creates heavy elements and isotopes which are strewn across the cosmos.
Data indicates that the debris spread over more than 1.5 million years, suggesting a series of supernova followed one after another.
In an article in the current issue of the journal Nature, Prof. Michael Paul from HU’s Racah Institute of Physics wrote: “Through data collected around the globe and analyzed in various nuclear physics labs, we found traces of an isotope of iron that is the fingerprint to series of supernovae exploding about two to three million years ago,” said.
The team also includes scientists from Australian National University (ANU), Austria’s University of Vienna, Japan’s Shimizu Corporation and Nihon University, and Germany’s Helmholtz- Zentrum Dresden-Rossendorf.
Dr. Anton Wallner from ANU and Prof. Paul from HU followed up the initial hints of iron-60 in samples from the Pacific Ocean floor, found a decade ago by a research group at Munich’s Technical University.
Using the ANU’s heavy ion accelerator, the scientists identified interstellar iron atoms in deep-sea sediment and crust samples taken from the Pacific, Atlantic and Indian Oceans. They found radioactive iron-60 – which decays with a half-life of 2.6 million years – was concentrated in a period between 3.2 and 1.7 million years ago. They also found evidence of iron- 60 from an older supernova, around 8 million years ago, which is relatively recent in astronomical terms.
The scientists believe the supernovae were less than 300 light years away, close enough to be visible during the day and comparable in brightness to the Earth’s moon.
The radiation would have been too weak to cause biological damage or trigger mass extinctions, but the cosmic rays from supernovae could have increased cloud cover, which impacted the Earth’s climate.