The question is "Where did our moon come from?" If we are to understand the origin of anything in space, it should begin with our nearest neighbor, the moon. Thousands of journal articles have been written and billions of dollars have been spent on lunar research. As a result of this has been a continuing parade of lunar origin theories.
Big Whack : An idea that 4.5 billion years ago, an object more massive than Mars slammed into the infant Earth so hard that the object's iron core plunged to the center of our planet causing some of the earth to break off and form into the moon after it condensed and cooled. Also called the Collision Theory.
Fission : The moon broke off from a rapidly spinning earth.
Capture : The moon, long ago, passed nearby the earth and was captured by the Earth's gravity.
Nebula : The Earth and moon formed side by side from collapsing dust clouds.
Each one of these ideas assumes a long time span for completion and also a basic randomness in nature. Which lunar origin theory is correct? Most likely none of them! The collision or big whack idea is quite popular at present, but it faces the same problems which doom the others : low probability, earth-moon chemistry differences, and dynamic difficulties.
Perhaps the best origin of the moon is Creation. God precisely placed it to circle the earth on the fourth day of creation (Genesis 1:16). Since then it has faithfully performed its ongoing functions of night light, calendar-clock, and tide generator for the earth. This miraculous lunar creation remains a credible alternative to the natural origin. After all, the moon is overhead, defying the best origin theories that experts and computers can produce. God created the moon for a purpose, as a shield for the earth, for time, but mainly as a lesser light compared to the greater light the sun. The moon does not produce light of its own but reflects the light of the sun. The moon was created to give God the glory. "The heavens declare the glory of God; and the firmament sheweth his handywork" (Psalm 19:1)(KJV).