Why Did It Take So Long for True Crust to Form

Multiple Choice

Why did it take so long for true crust to form on Earth?

A) because Earth had to complete the differentiation process before rocks could form
B) because temperatures were so high that any crust that did form was quickly remelted
C) because there was no atmosphere on the planet and thus no air to cool the crust
D) because heat from the creation of the magnetic field kept the surface molten