Comet or Asteroid Shower in the Late Eocene?

In the late Eocene [34 to 36.5 million years ago (Ma)], the deep-water carbonates of the Massig-nano section (Italy) were enriched in extraterres-trial 3He, indicating a higher delivery of interplan-etary dust particles (IDPs) to Earth (1). This2.5-million-year–long increase in the flux of IDPs is attributed to the arrival in the inner solar system of long-period comets, triggered by a perturbation of the Oort cloud (1). The two largest terrestrial craters in the Cenozoic, the 100-km Popigai (dat-ed 35.7 0.2 Ma) in northern Siberia and the 85-km Chesapeake Bay (dated 35.5 0.6 Ma) just offshore Virginia, formed during the same time interval (2); they are likely the result of cometary impacts (1)