 Another speculation points to several large meteorite impacts near this time, including those of the Chesapeake Bay crater and the Popigai crater of central Siberia, which scattered debris perhaps as far as Europe.New dating of the Popigai meteor strengthens its association with the extinction.A leading model of climate cooling at this time predicts a decrease in atmospheric carbon dioxide, which slowly declined in the mid to late Eocene and possibly reached some threshold approximately 34 million years ago.