The diagram below shows a stack of rock layers. examine the diagram, and answer the question that follows. 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, m, x, and g are all older than 100 million years. b. layers t and m are older than 100 million years, and layers x and g are younger than 100 million years. c. layers t, m, x, and g are all younger than 100 million years. d. layers t and m are younger than 100 million years, and layers x and g are older than 100 million years.