Radiometric dating gives the Popigai crater the same age as the Chesapeake Bay and Toms Canyon craters. Another important deposit of late-Eocene impact ejecta has been found in Italy. At an outcrop near the town of Massignano, researchers have identified a thin layer containing shocked minerals and a higher than normal concentration of iridium, both of which are impact indicators. The ejecta also contain an unusual assemblage of tiny spinel crystals that are enriched in nickel, additional evidence of a bolide impact. The geochemistry of the Massignano ejecta, however, does not match that of the Chesapeake Bay ejecta, so there is a strong suspicion that the Massignano material may have come from Popigai.
Research is under way to determine whether such a connection is plausible.
Recently, geochemical evidence has given rise to speculation that there may be additional sources for late-Eocene impact ejecta. The helium-3 enhancement lasted for about 2 million years, until the end of the Eocene. Farley interprets the extra helium-3 as evidence that Earth encountered a comet shower approximately 35 million years ago, which would suggest that the Chesapeake Bay, Popigai, and Toms Canyon craters were excavated by the shower. Though a few minor perturbations have been noted, no convincing cases of extinction have come to light so far. Perhaps the multiple late-Eocene impacts caused an environmental response not accounted for by current hypotheses.