Final answer:
The end of tectonic activity would require the cooling and solidification of the mantle, stopping the convection currents that move the tectonic plates. This is a long-term geologic process and is not expected to happen in the near future.
Step-by-step explanation:
Earth's tectonic activity could come to an end if the planet's internal heat engine cooled down sufficiently to solidify the mantle. This heat drives the convection currents that move the tectonic plates. If the heat were removed, plate tectonics would effectively stop, as would the related geological phenomena such as earthquakes, volcanic eruptions, and the building of mountain ranges. It's worth noting that this process is not imminent, and Earth's geothermal gradient indicates that tectonic activity will continue for billions of years.
Mantle solidification is a key event that can conclude tectonic processes, as seen on celestial bodies like the Moon, where geological activity has ceased. Cooling of Earth's interior is one potential natural way to halt tectonic movements. However, such a cooling is a slow and gradual process that spans geologic time scales, far exceeding human time frames and civilization's existence.
In contrast to Earth, some terrestrial planets have already experienced a halt in tectonic activity due to the cooling and solidification of their mantles. The lack of tectonic activity on these worlds is evident in the absence of recent geological reshaping of their surfaces, unlike the continuous action we observe on Earth.