> Either volcanic and geothermal activity or meteoric activity are the only likely culprits. Another possibility is abrupt changes in the flow of large bodies

> Either volcanic and geothermal activity or meteoric activity are the only likely culprits. Another possibility is abrupt changes in the flow of large bodies of waters affecting ocean circulation causing climate changes. One hypotheses is as the glaciers retreated the waters of the Missisppi river switched to flowing out of the St Lawrence river affecting North Atlantic currents.