Convection cells are created by very hot material deep in the mantle rising, then cooling, sinking again and repeating the cycle. This process occurs because of the uneven distribution of ? Within the earth? Please fill in the question mark with a answer. a. Crystal plates B. Plate convergence C. Convection waves D. Radioactive elements

A. Crustal Plates

The correct answer to fill in the question mark is D. Radioactive elements.

Convection cells in the Earth's mantle are created by the uneven distribution of radioactive elements within the Earth. These radioactive elements, such as uranium and thorium, decay and release heat. This heat transfer causes the material deep in the mantle to become hot and less dense, causing it to rise towards the Earth's surface.

As the hot material rises, it eventually cools down and becomes more dense, leading to its descent back towards the core. This continuous cycle of rising and sinking forms convection cells, which drive the movement of the Earth's tectonic plates. The convection cells transfer heat from the deep mantle to the surface, influencing various geologic processes like plate tectonics and volcanic activity.