Terrestrial Effects Of Nearby Supernovae In The Early Pleistocene

TL;DR

This study assesses the potential impact of nearby supernovae in the early Pleistocene on Earth's atmosphere and life, finding limited chemical effects but significant increases in radiation exposure that could influence climate and biological mutations.

Contribution

It provides a detailed analysis of the terrestrial atmospheric and biological effects of supernovae at 100 pc, highlighting radiation increases and their possible ecological implications.

Findings

Weak ozone depletion from supernova photon effects

Significant increase in ground-level muon radiation

Potential link to Pliocene-Pleistocene boundary extinction

Abstract

Recent results have strongly confirmed that multiple supernovae happened at distances ~100 pc consisting of two main events: one at 1.7 to 3.2 million years ago, and the other at 6.5 to 8.7 million years ago. These events are said to be responsible for excavating the Local Bubble in the interstellar medium and depositing 60Fe on Earth and the Moon. Other events are indicated by effects in the local cosmic ray (CR) spectrum. Given this updated and refined picture, we ask whether such supernovae are expected to have had substantial effects on the terrestrial atmosphere and biota. In a first cut at the most probable cases, combining photon and cosmic ray effects, we find that a supernova at 100 pc can have only a small effect on terrestrial organisms from visible light and that chemical changes such as ozone depletion are weak. However, tropospheric ionization right down to the ground due to the penetration of $\geq$TeV cosmic rays will increase by nearly an order of magnitude for thousands of years, and irradiation by muons on the ground and in the upper ocean will increase 20-fold, which will approximately triple the overall radiation load on terrestrial organisms. Such irradiation has been linked to possible changes in climate and increased cancer and mutation rates. This may be related to a minor mass extinction around the Pliocene-Pleistocene boundary, and further research on the effects is needed.