Geological Isotope Anomalies as Signatures of Nearby Supernovae

Nearby supernova explosions may cause geological isotope anomalies via the direct deposition of debris or by cosmic-ray spallation in the Earth's atmosphere. We estimate the mass of material deposited terrestrially by these two mechanisms, showing the dependence on the supernova distance. A number of radioactive isotopes are identified as possible diagnostic tools, such as ¹⁰Be, ²⁶Al, ³⁶Cl, ⁵³Mn, ⁶⁰Fe, and ⁵⁹Ni, as well as the longer-lived ¹²⁹I, ¹⁴⁶Sm, and ²⁴⁴Pu. We discuss whether the 35 and 60 kyr old ¹⁰Be anomalies observed in the Vostok Antarctic ice cores could be due to supernova explosions. Combining our estimates for matter deposition with results of recent nucleosynthesis yields, we calculate the expected signal from nearby supernovae using ice cores back to O(300) kyr ago, and we discuss using deep-ocean sediments back to several hundred Myr. In particular, we examine the prospects for identifying isotope anomalies due to the Geminga supernova explosion, and signatures of the possibility that supernovae might have caused one or more biological mass extinctions.