Researchers say cooling 13,000 years ago is coincident with major volcanic eruption.

Texas researchers from the University of Houston, Baylor University and Texas A&M University have discovered evidence for why the earth cooled dramatically 13,000 years ago, dropping temperatures by about 3 degrees Centigrade.

The evidence is buried in a Central Texas cave, where horizons of sediment have preserved unique geochemical signatures from ancient volcanic eruptions — signatures previously mistaken for extraterrestrial impacts, researchers say.