Actual paper http://www.pnas.org/content/early/2016/01/05/1515478113 http://www.pnas.org/content/early/2016/01/05/1515478113 Basically, they analyze isotope ra

Actual paper http://www.pnas.org/content/early/2016/01/05/1515478113 http://www.pnas.org/content/early/2016/01/05/1515478113 Basically, they analyze isotope ratios through the rock layers. Different weather patterns correspond with different isotope deposits. They were using this as a model to support an existing theory about a weather pattern that existed 70k to 55k years ago.