Two fossils found right next to each other are determined by radiometric dating to have similar levels of decayed isotope in their surrounding rock. Which of the following conclusions can be made?

(A) The two life-forms had the same molecular DNA sequence.
(B) The two life-forms were the same trophic level in an ecosystem.
(C) The two life-forms were part of the same community.
(D) The two life-forms are common ancestors to modern-day mammals.

Radiometric dating is a scientific technique based on predictable radioactive decay. The age of a rock or other substance that contains trace amounts of radioactive isotopes can be estimated by measuring how much of the original radioactive isotope is present and how much of the decayed version is present. Because the rate of decay occurs in an even, predictable manner, the original creation date of the rock can be estimated.