Study Suggests A Supernova Exploded Near Earth About 2.5 Million Years Ago, Possibly Causing An Extinction Event
Supernovas are amazingly bright explosions of massive stars at the end of their lives. During the gravitational collapse, the outer layers of the star are pushed away, and chemical elements formed inside the dying star are released into space. This cosmic dust rains down onto the Earth continuously, eventually becoming part of sediments deposited in the sea.
Research published in the journal Physical Review Letters used the concentrations of elements formed in an exploding star and preserved in oceanic sediments to hypothesize that a supernova exploded near Earth just 2.5 million years ago.
The authors, led by Dr. Gunther Korschinek from the Technical University of Munich, focused their study on ferromanganese crusts collected in the Pacific Ocean. Ferromanganese crusts form on the bottom of the ocean by layers of iron- and manganese-oxides precipitating out of seawater. The studied samples started to grow some 20 million years ago at depths ranging from 5,200 feet to 3.18 miles (approximately 1.600 to 5.120 meters). The researchers measured the concentrations of iron-60 and manganese-53 isotopes in the hardened crust. They differ from Earth’s most common form of the elements by their varying number of neutrons in the atomic nucleus. Both isotopes are synthesized in large stars shortly before supernova explosions and are unstable, decaying completely after 4 to 15 million years. Their presence in sediment samples is evidence for Earth passing through a cloud of cosmic dust generated by an exploding star in – geologically speaking – recent times.