How a nearby supernova left its mark on Earth life
When a massive star explodes as a supernova, it does more than release an extraordinary amount of energy. Supernovae explosions are responsible for creating some of the heavy elements, including iron, which is blasted out ...
On Earth, there are two accumulations of the iron isotope 60Fe in sea-floor sediments that scientists trace back to about 2 or 3 million years ago and to about 5 to 6 million years ago.
The explosions that created the iron also dosed Earth with cosmic radiation.
In new research submitted to The Astrophysical Journal Letters, scientists examine how much energy reached Earth from these explosions and how that radiation may have affected life on Earth.
The paper is titled "Life in the Bubble: How a nearby supernova left ephemeral footprints on the cosmic-ray spectrum and indelible imprints on life," and it is available on the arXiv preprint server. The lead author is Caitlyn Nojiri from UC Santa Cruz.
"Life on Earth is constantly evolving under continuous exposure to ionizing radiation from both terrestrial and cosmic origin," the authors write. Terrestrial radiation slowly decreases over billions of years. But not cosmic radiation. The amount of cosmic radiation that Earth is exposed to varies as our solar system moves through the galaxy.
"Nearby supernova (SN) activity has the potential to raise the radiation levels at the surface of the Earth by several orders of magnitude, which is expected to have a profound impact on the evolution of life," they write.
Artist's impression of a supernova. Supernovae bombarded Earth with radiation that has implications for the development of life on Earth. Credit: NASA
The left panel shows the Local Bubble and nearby stellar associations, while the right panel shows their galactic coordinates. The right panel also shows a new Galactic bubble discovered in 2018. It’s likely the remnant of an SN that exploded in Upper Centaurus Lupus. Credit: Nojiri et al. 2024
This figure shows the average dose rate experienced at ground level as a function of the distance to the nearby SN. The average dose is calculated over the first 10 kyr (solid line) and over the first 100 kyr (dashed line) after the SN explosion. It’s not enough to trigger an extinction, but it could’ve driven species diversification. Credit: Nojiri et al. 2024