GEOCHEMICAL EVIDENCE FOR A COMET SHOWER IN THE LATE EOCENE

Analyses of pelagic limestones indicate that the flux of extraterrestr ial helium-3 to Earth was increased for a 2.5-million year (My) period in the late Eocene. The enhancement began similar to 1 My before and ended similar to 1.5 My after the major impact events that produced th e large Popigai and Chesapeake Bay craters similar to 36 million years ago. The correlation between increased concentrations of helium-3, a tracer of fine-grained interplanetary dust, and large impacts indicate s that the abundance of Earth-crossing objects and dustiness in the in ner solar system were simultaneously but only briefly enhanced. These observations provide evidence for a comet shower triggered by an impul sive perturbation of the Oort cloud.