Book excerpt: Covers the truly varied roles carbon dioxide has played and continues to play in the character of our planet. Chapters deal with the synthesis of CO2 in stars, the evolution of the atmosphere over billions of years, the chemical and physical properties of CO2 and how those influence common phenomena. How well this knowledge is understood and how it was determined, including existing uncertainties in our confidence and the stress from competing possibilities are discussed. Much of the technological jargon in various incorporated sciences has been modified to ease consumption by the non-expert.