This unit allows students to investigate past changes in Earth's climate. Students first explore relationships in climate data such as temperature, solar radiation, carbon dioxide, and biodiversity. They then investigate solar radiation in more depth to learn about changes over time such as seasonal shifts. Students then learn about mechanisms for exploring past changes in Earth's climate such as ice cores, tree rings, fossil records, etc. Finally, students tie all these together by considering the feedbacks throughout the Earth system and reviewing an article on a past mass extinction event.

Here students use data from the NOAA carbon dioxide monitoring sites, such as Mauna Loa, to graph the Keeling Curve for themselves on large sheets of paper. Each group graphs one year, and the graphs are joined at the end to reveal the overall upward trend. The explanation describes the carbon cycle and how human activities are leading to the overall trend of rising carbon dioxide.