|| Discussion of what methods we use for understanding the history of environmental change on our planet, and talk about examples of extreme climate change in Earth's history that have recently been discovered and are enigmatic. Questions addressed include: How do we know that CO2 levels have now reached levels that are unprecedented over the past million years? What impact do changes in levels of CO2 have on temperature? What has happened to climate in the past when 5000 gigatons of carbon were released into the atmosphere? Why do we think that the Earth's oceans completely froze over, and how did we get out of this bizarre snowball situation? What do we know? And what do we still need to find out?