Most people know that the Earth is about 4.6 billion years old but few know how scientists piece together the evidence to make this estimation. In this session, we will learn about the “history of the history of the Earth” and analyze the various types of data that are used to determine the age of the Earth and Universe. We’ll use this data to build a model for how the Earth has changed over time. The activities in this session are designed to promote critical thinking about the validity of different methods and constructing explanations based on evidence. The session focuses on Utah SEEd Standards Strands 7.2 and 7.5, but is appropriate for those teaching any Earth Science topic or the Theory of Evolution. Topics include the Geologic Time Scale, relative and absolute dating, the fossil record, evolution and extinction of life, and radioactive decay.