Go to next question A8 . Consider three undeformed horizontal beds of sedimentary rock. The layer on top is the oldest. The middle layer is the oldest. The layer on the bottom is the oldest.
More information is needed to determine which layer is oldest.
The layer on the bottom is oldest. Go to next question A9 . A rock formed with 1,000 atoms of a radioactive parent element, but contains only 250 radioactive parent atoms today. Here's how it works. So we can see 2 half lives have gone by, and the half life is 1 million years, so the rock must be 2 million years old.