Researchers say they’ve found evidence of supernova explosions that spewed radioactive fallout over Earth during the age when humanity’s ancestors were evolving into upright-walking, big-brained creatures.
One of two studies published in the journal Nature identifies deposits of radioactive iron-60 in deep-sea cores extracted from the bottom of the Indian, Pacific and Atlantic oceans. The deposits were traced back to one time frame ranging from 1.5 million to 3.2 million years ago, and another period 6.5 million to 8.7 million years ago.
The researchers behind that study, led by Anton Wallner of Australian National University, say the iron-60 was blasted toward us by “multiple supernova and massive-star events” that occurred within 325 light-years of Earth.
Today, this region of space is known as the Local Bubble. The region was given that name decades ago, because even back then, scientists surmised that the “bubble” of hot, diffuse gas in our celestial neighborhood was created by a cluster of supernova explosions.
The other study in Nature, conducted by Dieter Breitschwerdt of the Berlin Institute of Technology and his colleagues, took a closer look at the more recent iron-60 deposit to trace its origins.
They say it’s most likely that that two supernovae were responsible: One would have occurred 2.3 million years ago, involving a star 9.2 times as massive as the sun. The other would have happened 1.5 million years ago, when a star 8.8 times as massive as the sun blew up.
The supernovae would have been as bright as the full moon, and could have been seen during the day, the researchers say.
“This research essentially proves that certain events happened in the not-too-distant past,” Adrian Melott, an astrophysicist at the University of Kansas who was not involved in either study, said in a news release.
“They make it clear approximately when they happened and how far away they were. Knowing that, we can consider what the effect may have been with definite numbers. Then we can look for events in the history of the Earth that might be connected to them.”
Melott said none of the events occurred within a “kill zone” of roughly 30 light-years, which means it’s unlikely that any of them sparked a mass extinction.
However, the more recent explosions rained fallout on our planet during the time when human ancestors were making the transition from early types such as Australopithecus, represented by the famous Lucy fossil, to the bigger-brained type represented by Homo habilis.
Melott said there’s a chance that the supernovae had an impact on human evolution.
The evolutionary link could come about through two potential effects. Some scientists suggest that the cosmic rays released by nearby supernovae could have contributed to cycles of colder temperatures on Earth, such as the ones that occurred about 8 million years ago and 2.6 million years ago.
In a news release, Wallner said the correlation between the supernovae and the cooling periods was “an interesting coincidence.”
“This climatic variation may be one of the conditions that led to human evolution,” Melott said in a Nature commentary.
The other effect may have been related to the radioactive iron-60, Breitschwerdt told Space.com. “It might be possible that an increased rate of mutations directly influenced evolution – for example, increase in brain size,” he said.
The link between stellar blasts and human evolution is far from proven, but the mere idea is a mind-blower of supernova proportions.
In addition to Wallner, the authors of “Recent Near-Earth Supernovae Probed by Global Deposition of Interstellar Radioactive 60Fe” include J. Feige, N. Kinoshta, M. Paul, L.K. Fifield, R. Golser, M. Honda, U. Linnemann, H. Matsuzaki, S. Merchel, G. Rugel, S.G. Tims, P. Steier, T. Yamagata and S.R. Winkler.
In addition to Breitschwerdt, the authors of “The Locations of Recent Supernovae Near the Sun From Modelling 60Fe Transport” include J. Feige, M.M. Schulreich, M.A. de Avillez, C. Dettbarn and B. Fuchs.
