Illustration of a supernova explosion. (Photo credit: NASA/CXC/M. Weiss)
A recent study suggests that radiation from an exploded star may have had a significant impact on the development of life on Earth.
Around 2.5 million years ago, viruses infecting fish in Africa's Lake Tanganyika experienced a mysterious and rapid burst of diversity. But the exact reason for this change remains unclear.
Now, a new study has found that the increase in viruses detected in the lake coincided with a period when our planet was being bombarded with cosmic rays from an ancient supernova, suggesting a possible link between the two events. The researchers published their findings Jan. 17 in The Astrophysical Journal Letters.
“It’s fascinating to discover ways in which such distant events can impact our lives or the conditions for life on the planet,” lead author Caitlin Nojiri, an astrophysicist at the University of California, Santa Cruz, said in a statement. “We know from other studies that radiation can damage DNA. This can be a catalyst for evolutionary changes or mutations in cells.”
Lake Tanganyika, located in East Africa’s Great Rift Valley, is one of the largest freshwater lakes on Earth. It covers an area of approximately 12,700 square miles and is shared by four countries – Burundi, the Democratic Republic of the Congo (DRC), Tanzania, and Zambia. The lake is home to over 2,000 species, more than half of which are found nowhere else. This makes it a unique place, according to the World Conservation Union, which states that “no other place on Earth can boast such a diversity of life.”
One factor that may have contributed to this diversity, the study authors believe. Scientists already know that high-energy particles from space, known as cosmic rays, can damage astronauts' cells, causing accelerated aging, and that their effects may be linked to the structural preferences of biological molecules known as chirality. However, how significant a role these cosmic rays play in evolutionary history has not yet been explored.
To find out, the researchers working on the new study extracted and analyzed core samples from the sea floor. They found that it contained an isotope of iron called iron-60, which is typically formed in stellar explosions. By radioactively dating this isotope, they found that the iron-60 in their sample fell into two distinct periods: one that occurred 6.5 million years ago and one that was 2.5 million years old.
To trace the isotope's origins, the researchers modeled the Sun's motion through the Milky Way. They found that about 6.5 million years ago, our solar system and star crossed the Local Bubble, a region of low density in the Orion arm of the Milky Way filled with debris from exploded stars.
Further analysis showed that the later burst likely came from a supernova, either from a cluster of young stars in the Scorpius-Centaurus constellation, 460 light-years away, or from the Tucana-Horse cluster, 230 light-years away. When modeling the explosion of a star near Earth, the scientists found that such an event would have showered Earth with cosmic rays for 100,000 years after the initial explosion, consistent with the burst recorded in the sediment.
If their hypotheses are correct and this event did occur, it was powerful enough to penetrate the Earth's atmosphere and break DNA strands, which could explain the dramatic increase in the diversity of viruses found in Lake Tanganyika.
While scientists cautioned that the link was not conclusive, it raised the possibility that powerful cosmic events could have had a more significant impact on the formation of life on our planet.
Sourse: www.livescience.com
