May 9, 2013
First Biological Evidence On Earth Of Ancient Supernova
John P. Millis, PhD for redOrbit.com — Your Universe Online
In the early Universe the only elements capable of forming were hydrogen and helium. All subsequent atoms are created by massive stars: the lighter members by nuclear fusion in their cores, with much of the rest created during supernovae as atoms are collided at incredible energies leading to nucleosynthesis. Some of the elements produced have long half-lives, sticking around to lay the foundation for new stars, planets and interstellar gas clouds. Other elements produced in the supernovae blasts are short lived.
In the specific case of isotope Iron-60, the 2.62 million-year half-life means that none should naturally exist on Earth. However, in 2004 scientists from the Technische Universitaet Muenchen (TUM) unexpectedly found the iron radioisotope in the Earth´s crust along the ocean´s floor. Geological dating indicates that the iron had been embedded for about 2.2 million years.
But to confirm the findings, nuclear astrophysicist Shawn Bishop and his colleagues from TUM looked to a special type of bacteria that lurk along the ocean floor near the water-sediment interface. Within their cells the bacteria make magnetite (Fe3O4) crystals, drawing the needed iron from the ocean floor.
Therefore a percentage of the fossilized crystals, which long outlive their bacterial creators, should contain the Iron-60 radioisotope. The team studied “magnetofossils” estimated to have originated some 1.7 to 3.3 million years ago.
Separating the samples into 100,000-year bands, they searched for the presence of Iron-60 in the crystals. A sudden increase in Iron-60 was found 2.2 million years ago, corroborating the 2004 results.
According to Bishop, “It seems reasonable to suppose that the apparent signal of Fe-60 could be remains of magnetite chains formed by bacteria on the sea floor as a starburst showered on them from the atmosphere.”
The TUM team is now combing through an even bigger dataset to determine whether the 2.2 million year-old signal is still present. If it is, this will indicate the first biological evidence of an ancient supernova.