Actual paper <a href="http:&#x2F;&#x2F;www.pnas.org&#x2F;content&#x2F;early&#x2F;2016&#x2F;01&#x2F;05&#x2F;1515478113" rel="nofollow">http:&#x2F;&#x2F;www.pnas.org&#x2F;content&#x2F;early&#x2F;2016&#x2F;01&#x2F;05&#x2F;1515478113</a><p>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.