In this excerpt from "This is Life: A Journey from Inside Your Body to Beyond Earth," author and physicist Christophe Galfard explores the way 19th century scientists were starting to use thermodynamics to understand just how old Earth is.
Source: [Live Science](https://www.livescience.com/physics-mathematics/no-one-dared-question-his-results-how-thermodynamics-sparked-a-heated-debate-about-earths-age-in-the-19th)