Giant CAVITY Inside the Moon? Conspiracy or Scientific Fact?

On earth, the newest rocks are at the surface, and the rock gets older as you go deeper. This is obvious and logical, but on the moon, the soil on the surface is older than the rocks underneath, and the surface rocks are older than the rock underneath them. It's backwards. Normal planetary composition results in heavier elements in the core and lighter materials at the surface; not so with the moon. Moon rocks were magnetized. This is odd because there is no magnetic field on the moon itself. This could not have originated from a "close call" with Earth - such an encounter would have ripped the moon apart. The moon's mean density is 3.34 gm/cm3 whereas the Earth's is 5.5. Although the satellite is a quarter of Earth's eight thousand mile diameter, it only has 1.2% of the mass. Four moons should theoretically be equivalent to one Earth. In reality, it would take over eighty-one moons to produce our terrestrial world's total mass. What does this mean?