Seasonal variations on Mars are more extreme than those on Earth because Mars is further from the Sun. The interior of the Earth is hot because radioactive heating has kept it hot since it formed. A sample of rock contains one quarter of its original amount of a radioactive isotope. The statement that the Earth is differentiated refers to the radial stratification of the Earth by density. Plates are destroyed at subduction zones.
All volcanic activity occurs at subduction zones.
Plates are created at mid-ocean ridges. The Earth's lithosphere is broken into plates. Most earthquakes occur at plate boundaries. The bending of seismic waves in the interior of the Earth. Because we know the temperature is high enough to melt iron.