Most of the moon came from Earth. In fact Earth is much denser than most planets of similar size because it contains many heavy metals that came from beyond our solar system. Early in Earth’s pre-Moon history, our fragile little planet was struck by an extrasolar object roughly the size of Mars. This object was composed primarily of heavy metals and accounts for the giant ball of iron that is Earth’s core. This was not an ordinary collision; this was the ultimate trick shot. The only collision model that accounts for the measurable data is that the planetoid had to strike Earth at a severely oblique angle. According to mathletes, it collided with Earth at roughly 4 mph. A faster impact would have destroyed Earth and made it into another asteroid belt. A slower impact or one slightly off course would have resulted in a glancing blow and both objects would go off on their merry way. But the oblique impact fused Earth and the planetoid together, eventually subsuming all the dense matter into Earth’s core. Hundreds of thousands of tons of other material was blown off the Earth and all of that eventually became the moon.
Well that’s interesting you may be thinking, but moon, no moon, what difference does it make? Earth could not support advanced life without the moon. Without the moon to act as a stabilizer, an Earth day would be approx @6 hours. A planet spinning that fast would cause the atmosphere to be covered with violent hurricanes and tidal waves. There would not be the shallow, stable oceans where bacterial life lived for billions of years. Without the moon we would have no tidal activity. The moon also acts as a gravitic shield, absorbing many dangerous cometary and meteor impacts (a look at the surface of the moon is a testament to that). Also without all of those heavy metals that were delivered from some mysterious extraterrestrial source, we would not have the abundant thorium and uranium needed to have plate tectonics.