The diagram shows the rock layers of two mountains, labeled A and B. The two mountains are located thousands of kilometers apart, on different continents. Both mountains have a layer of limestone, as shown by the labels. A scientist analyzes a fossil found in the limestone layer of Mountain A. By applying the technique of radiometric dating to the fossil, the scientist concludes that the limestone formed approximately 1.34 billion years ago. Which two assumptions are necessary to support the scientist's conclusion? Select the two correct answers.
A. After the fossil formed, all of its radioactive isotopes decayed very quickly.
B. Radioactive isotopes decay at a constant rate over long spans of time.
C. The fossil formed at the same time as the limestone surrounding it.
D. The fossil formed from the same materials as the limestone surrounding it.
E. After the limestone formed, chemical and physical processes affected it only minimally.