Answer:
The heat from radioactive processes within the planet's interior causes the plates to move, sometimes toward and sometimes away from each other.
Step-by-step explanation:
The plates can be thought of like pieces of a cracked shell that rest on the hot, molten rock of Earth's mantle and fit snugly against one another. The heat from radioactive processes within the planet's interior causes the plates to move, sometimes toward and sometimes away from each other.