1. The average thickness of the Earth's oceanic lithosphere is about 60 km, representing the cooling of oceanic plates as they move away from spreading ridges. The approximate oceanic lithospheric age corresponding to this average thickness is ~100 Ma. By contrast, the average thickness of the lithosphere of Mars is at least ~300 km, as determined by studies of loading of the Martian lithosphere by huge volcanoes such as Olympus Mons.

(a) Assuming that Mars' mantle is of similar composition and physical properties as Earth's mantle, and that the temperature difference between the Martian interior and surface is similar to that of the Earth, what is the approximate average thermal age of Mars' lithosphere?

(b) How is the above result likely related to the fact that Mars has not experienced plate tectonics for at least the last ~2-3 billion years?