Nov. 2, 2004 — A stellar blast might have helped initiate human evolution three million years ago, according to German scientists who have found clear traces of an ancient supernova explosion deep beneath the Pacific Ocean.

Sifting through dust on the ocean floor at a depth of 15,750 feet, Gunther Korschinek and colleagues at the Technical University of Munich in Germany found 28 layers of iron-60, a radioactive isotope of iron which experts believe is unlikely to have come from anything other than the heat, pressure and nuclear activity of a supernova.

"Fe-60 (iron-60) is a unique indicator for the detection of supernova debris on Earth," the researchers wrote in the latest issue of Physical Review Letters.

With a decay rate of about 1.5 million years, this long-lived chemical variant of iron can also have a key role in helping to date supernova explosions.

According to Korschinek's team, the iron-60 layers indicate that the star exploded 2.8 million years ago at a distance from Earth of a few tens of parsecs (1 parsec is approximately 3.26 light-years), showering down not only solid matter in the form of iron, but also cosmic rays.

"For the first time, we were able to carry out a detailed calculation for the increase in cosmic radiation, as well as for the duration. The result suggests an increase of only a few percent, but a very long duration of some hundred thousand years," Korschinek told Discovery News.

Lasting for that long, the cosmic ray flux from the supernova explosion could have heated up the Earth, forcing a climate change in Africa.

Though it has not yet been established that such an increase of the cosmic ray intensity could have had a significant influence on the Earth's climate, the researchers noted a coincidence between the onset and the duration of the cosmic ray flux and a change in the African climate.

"The African climate shifted toward more arid conditions about 2.8 million years ago ... . Some of the major events in early hominid evolution appear to be coeval with the African climate changes," the researchers wrote.

Indeed, anthropologists believe that the dramatic African climate changes, resulting in deforestation and the emerging of savannah, forced hominins to climb down from the trees and walk erect.

"The idea that a supernova exploded in our vicinity within the last few million years has traction and seems credible. That it contributed a layer of long-lived radioactive species — not just Fe-60 — also seems rather sensible. It will be important to determine the expected spread in arrival times, as well as to detect the other unstable isotopes expected, such as Mn-53, Cl-36, Al-26, Pu-244, etc.," supernova expert Adam Burrows, professor at University of Arizona's department of astronomy, told Discovery News.

"I would be loathe at this stage to credit the idea that this event stimulated the evolution or migrations of humanity," he added.