A fossil discovered in Colorado dates from the early Mesozoic era. A year later a similar fossil is found in Wyoming that also dates from the early Mesozoic era. These two organisms most likely lived in A. the same environment at about the same time.
B. the same environment at different times.
C. different environments at about the same time.
D. different environments at different times.

A. the same environment at about the same time.

Explanation:

Radioactive elements have a half-life (decay time) and a decay rate which is dependent on the decay constant. These informations when properly obtained can be used to determine the age of any historical monument or material such as earth, rocks, animals, plants, etc., because the parent material decays into a stable daughter elements at a constant decay rate.

In this scenario, a fossil discovered in Colorado dates from the early Mesozoic era. A year later a similar fossil is found in Wyoming that also dates from the early Mesozoic era. Therefore, these two organisms most likely lived in the same environment at about the same time.

Even though the fossils were obtained in different locations (Colorado and Wyoming), the singular fact that they were similar and dated back to the same Mesozoic era suggest that the two organisms most likely lived in the same environment at about the same time before one of them migrated.