Supernovae, the explosive deaths of massive stars, unleash immense energy that can ripple across vast distances—even reaching Earth. A groundbreaking study from the University of Colorado Boulder has uncovered evidence of these cosmic events preserved in ancient tree rings.
A supernova is a colossal stellar explosion that briefly outshines entire galaxies. When one occurs in Earth's cosmic neighborhood, it can spike cosmic ray levels, triggering thunderstorms, wildfires, ozone depletion, ice ages, genetic mutations, or even mass extinctions.
More subtly, these events may imprint traces in tree rings. Researchers from the University of Colorado Boulder analyzed this in a study published November 4, 2020, in the International Journal of Astrobiology. They identified at least four climate disruptions over the past 40,000 years tied to nearby supernovae.
The team measured carbon-14 levels in tree rings—a radioactive isotope produced when cosmic rays hit the atmosphere and absorbed by growing trees, just like regular carbon.
Scientists observed sharp carbon-14 spikes in tree rings uncorrelated with Earth-based events. Two explanations emerged: extreme solar flares or nearby supernovae. The latter prevailed, supported by historical records of gamma-ray bursts from extragalactic supernovae.
By cataloging the eight closest supernovae from the last 40,000 years and cross-referencing with tree-ring data, researchers linked them to these spikes. For instance, a star in the Veil Nebula, 815 light-years away, exploded around 13,000 years ago, boosting Earth's carbon-14 by nearly 3% shortly after.
Challenges persist, especially in precise dating—researchers note a potential 1,500-year margin of error for some events. Refining these measurements will strengthen the supernova-tree ring connection.
