Layer R contains a well-known index fossil that is 100 million years old. Based on this information and the principle of superposition, A. Layers T and M are older than 100 million years, and Layers X and G are younger than 100 million years. B. Layers T, M, X, and G are all older than 100 million years. C. Layers T and M are younger than 100 million years, and Layers X and G are older than 100 million years.