Figure 11.7

Relative age and the principle of superposition. (A) The layers of sand poured into this glass represent sedimentary rock layers that have formed from sand over time. The layer at the bottom was deposited first and is older than the top layer. (B) The Colorado River has cut the mile-deep Grand Canyon in northern Arizona, exposing rock layers that were first deposited 1.7 billion years ago. Rocks at the top of the canyon are younger than those below.
(B. © Michael Runkel/Robert Harding World Imagery/Alamy)