Late Quaternary supernovae in Earth history

ABSTRACT Supernovae (SNe) may have affected Earth's atmosphere during Late Quaternary (50 ka-present) time and be detectible in cosmogenic isotopic records. Supernova remnants (SNRs) at distances <2.3 kpc provide a revised chronology of SNe and predicted hard photons received by Earth. Calculated fluences assume X-ray and γ isotropic emissions of 4 × 1049 erg within 2 yr. Such are compatible with high-energy observations of extragalactic SNe. Earlier values may be unrealistically small given current knowledge. The radiation events associated with nearby SNRs are compared to dated records of terrestrial environmental changes. Eight SNe may have produced hard photon fluences of 1–6 × 1024 erg on the terrestrial disc; they were at distances ≤0.6 kpc. The Vela SN (0.29 kpc) produced the highest fluence, at ∼13 ka. Its predicted environmental effects include abruptly elevated atmospheric 14C, reductions in upper atmosphere O3 and CH4, increased solar UVB at Earth's surface, possible cooling of the global climate, selective animal extinctions, increased wildfires, and Pt-group dust deposition. All are recorded in terrestrial records commencing at 12.76 ka and the start of the Younger Dryas cold period. Several thousand years earlier, the Hoinga SN (∼0.35 kpc, ∼15 ka) may have caused a single year 30‰ Δ14C rise at 14.32 ka and the Older Dryas cool period. The 14C production dropped to its previous level by 14.23 ka but a subsequent increase occurred 14–13.9 ka and may record the arrival of associated cosmic radiation. Δ14C events at 9.126, 7.209, 2.764, 2.614, 1.175 ka, and 0.957 ka were apparently global and each have plausible SNe candidates of appropriate distances and ages. The nearest SNe appear to be associated with the largest isotope anomalies.