I don't understand this at all.
Scientists have studied the radioactivity of rock samples in Earth's crust and the very top part of Earth's mantle. Because samples of rock have not been collected from deep within Earth, there is no data to show the specific levels of radioactive material throughout Earth's interior. However, some scientists believe that there is a higher concentration of radioactive elements in a layer of Earth's mantle, which would help to explain a driving force for the convection in Earth's mantle. Identify which part of the mantle scientists believe the radioactive material is concentrated in and how this concentration would help drive convection.