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 Ea rth's atmosphere. We estimate the mass of material deposited terrestri ally by these two mechanisms, showing the dependence on the supernova distance. A number of radioactive isotopes are identified as possible diagnostic tools, such as Be-10, Al-26, Cl-36, Mn-53, Fe-60, and Ni-59 , as well as the longer-lived I-129, Sm-146, and Pu-244. We discuss wh ether the 35 and 60 kyr old Be-10 anomalies observed in the Vostok Ant arctic ice cores could be due to supernova explosions. Combining our e stimates 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 sedi ments back to several hundred Myr. In particular, we examine the prosp ects for identifying isotope anomalies due to the Geminga supernova ex plosion, and signatures of the possibility that supernovae might have caused one or more biological mass extinctions.