Answer:
Geological activity would die and earth's interior would solidify
Explanation:
If earth's interior cools down, minerals that are now melted and flowing in the mantle would start to precipitate until form rocks, if everything is solid anything is going to flow as convection currents, it implies that geological activity stops. Then there wouldn't be tectonics, which is the responsable of volcanic activity, earthquakes, mountains growth, oceanic rifting and others.
