Layer A is the bottom layer with images of a trilobyte and a fan shaped shell. Layer B is above layer A with images of a fan shaped shell and a cone shaped shell. Layer C is above layer B with images of a fan shaped shell and a spiral shaped shell. Layer D is the top layer with an image of a cone shaped shell.
Use what you know about relative dating to choose the correct answers from the drop-down menus.

Ethan determines that layer B is 3.5 million years old. Due to the , he can estimate that layer A is years old.