Students will develop a mathematical model of the relationship between atmospheric CO2 and the number of stomata on a leaf (Stomata Index). They will evaluate the model graphically, statistically, and biologically, and then use it to estimate CO2 levels in the distant past. This module guides students through building a mathematical model of a biological relationship, evaluating the model, improving it, and then using the model. The biological context is global climate change and atmospheric CO2…