Earth's crust becomes a cooler solid. Earth's mantle becomes a warmer semiliquid. Earth's mantle becomes cooler and solid. Earth's outer core becomes warmer.
Which of the following changes would end Earth's tectonic activity?

Options:
- Earth's crust becomes a cooler solid.
- Earth's mantle becomes a warmer semiliquid.
- Earth's mantle becomes cooler and solid.
- Earth's outer core becomes warmer.

Earth's mantle becomes cooler and solid.