
Rock Rings Reveal New Insights About North America's Climate Past - curtis
http://gizmodo.com/rock-rings-reveal-surprising-new-insights-about-north-a-1752556296
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dexwiz
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.

