Hello,The moon is very interesting in its build and how it was made.the most acceptable theory today (most acceptable not meaning it's 100% true), is this: the moon as we see it now was formed when earth was very very young, at some stage of very very young earth a large Iron and nickel meteorite collided with the planet and threw several changes 2 things happed a)earth didn't brake apart to become an asteroid belt but held on b) the asteroid threw some changes became earth main Iron core that spins in the center of the earth.(a little wiled concept but this is a theory).Now in that Impact a lot of ejecta was flung in to space and because clumps of rock carry some gravitational power those rocks become moons for earth, over time those clumps of rock kept colliding with each other and little by little they all formed the moon as we know it.Now the moon might had a thin atmosphere when it was very very young but this is my theory but since the moon has a very very weak gravity the atmosphere dissipated in to space.
over time and because there is no atmosphere to protect it's surface the moon was (and still it) bombarded by meteorites from space, each impact brought the older brigter oil out from within the moon and the darker younger material is where no real major impact occurred. I would also guess that there was at some point some tectonic power in the moon that most of it faded now so changes in the topography also contributed to the deference's in the soils of the earth.