Debris containing iron from a star that exploded 2.2 million years ago was consumed by bacteria on earth, scientists have discovered. This is the first biological signature from an event in deep space.
Scientists led by Shawn Bishop of the Technical University of Munich in Germany analysed samples of sediment core from the bottom of eastern equatorial Pacific Ocean, dating to between about 1.7 million and 3.3 million years ago, scientific journal Nature reported. They found that there were traces of iron-60 in the 2.2 million year old layer. Iron-60 is an isotope of iron that does not form on Earth.
Preliminary findings were reported at a meeting of the American Physical Society in Denver, Colorado.
Certain types of bacteria that live on ocean floors consume iron to make tiny magnetic crystals and use it as an internal compass to guide them to better conditions. These are called 'magnetotactic' bacteria.
Bishop's analysis showed minuscule levels of iron-60 which could be in fossilized remains of these bacteria that existed 2.2 million years ago.
Although it is not clear as to which star exploded around that time, Nature suggested that it might be in the Scorpius-Centaurus stellar association, at a distance of about 424 light years from the Sun.
Star explosions are called supernova and they are thought to spew many elements including metals at enormous speed. They also emit high energy radiation like gamma ray bursts, thought to have caused the Ordovician-Silurian extinction in which 60 percent of life perished some 450 million years ago.
In 2004 iron-60 was discovered for the first time in a sample taken from the Pacific Ocean floor. Scientists calculated that it had arrived from some supernova in the distant past.
"For me, philosophically, the charm is that this is sitting in the fossil record of our planet," Bishop told Nature. He and his team are now working on a second core, also from the Pacific, to see if it too holds the iron-60 signal.
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