We know that the Earth’ mantle and core are hot, whereas the crust has cooled down. The cooling process of the 4,5 billion years of the Earth’ exisence resulted a crust of between 50 and 100 kms. Mars and Moon have a much much thicker crust. Earth has a larger mass consequently a larger surface to lose heat through. Earth’ heat is used to move continents around in tectonic moves, and allowing newly formed crust too cool and then sink back into the mantle, using up heat to melt back into it. No such tectonic movement is on the Moon or on the Mars. So why then that Earth’ crust is so thin?
The moon has cooled faster because it is so small and has less volume per unit of surface area. Lack of an atmosphere might also be a factor. Mars is also small compared to the Earth, has a tenuous atmosphere which makes a very poor blanket, and is about 40 million miles further away from the sun. Small things cool faster than large ones, a fact you can easily test for yourself by filling an egg cup with hot tea at the same time that you fill your normal cup.