Yael: So Don, I was reading this very interesting article about how in prehistoric times the world cooled because there was a sharp drop in carbon dioxide in the atmosphere.

• 所以说，东，我不久前看了一篇有趣的文章，这篇文章解释说在史前时代世界是怎么因为大气层的二氧化碳含量的减少而慢慢变冷的。