The Asteroid Belt, full of gravel and boulders, did not get there by accident. When your Solar System, forming matter, was into clumping matter together, and did
not overlook this one little orbit around this one little Sun for some odd reason. For those who argue otherwise, we ask why all the other planetary orbits are free of
this scatter, and why the Earth is lopsided, the land in the main on one side and the waters in the main on the other. The two relate. Long before there was highly
evolved life on the Earth, it rode that orbit, which happened to be smack dab in the path of the 12th Planet. In due time, more than violent pole shifts and wobbly
orbits resulted, a monumental collision between the emerging Earth and a traveling moon drawn along by the gravitational pull of the 12th Planet occurred. This
collision did not just involve the emerging Earth, then almost entirely a water planet.
Your Solar System had several more planets in orbit than it does today, in orbit close enough to the Asteroid Belt to be considered within it, many of these planets were larger than the Earth.. Just as the 12th Planet drags behind it many moons, these planets also had moons, so the field was crowded during the 12th Planet's periodic passage. The repulsion force prevents large object of a similar size from impact, because the flow of gravity particles acts like a firehose pointed toward one another, the colliding spray of the particle flow pushing back and away, at the same time the return flow of these gravity particles is pulling the two planets toward each other. But when any inequity of size exists, the repulsion force weakens. The greater the inequity, the greater the weakness. The firehose from the smaller object is overwhelmed by the return flow of gravity particles returning to the larger object. Thus, a large boulder would drop to Earth, but your Moon does not.
The Asteroid Belt was created when trash in the 12th Planets tail crashed into moons of some of the large planet in the Asteroid Belt, putting them in motion so that they became missiles directed at other planets. Eventually with all this bumping around in a crowded field, the inequity was great enough, the size disproportionate enough, that shattering of a small planet occurred. Magma sprayed outward in a burst, creating hardened magma in space which then itself became a missile on the move. Once begun, this process accelerates, creating increasing incidences where a piece of trash is large enough to shatter a planet. The planets disintegrate not because the missile is so large it physically breaks it apart, but because the molten core is opened, forcefully, and the lava pushed outward in a plume by the missile. Now the crust implodes, and the repercussions of this cause more magma plumes, so that the planet eventually does not have the mass to prevent a collision, by virtue of a repulsion force. Thus these wasted shells eventually collide with each other, breaking them into what you now term asteroids.
Matter went in every direction and the impacts were fierce. Shattered matter, moving at differing speeds, bumping into each other and slinging off into different directions, were missiles of death for some time. One disaster followed another, until at last there were no more hapless planets to be pelted into pieces. The Earth, her waters scattered more readily than her bulk, wobbled out of orbit at the initial impact. Her wobble took her, eventually, into her present orbit, closer to the Sun. Here she has formed her present oval shape bit by bit, under the periodic visits of her larger brother, the 12th Planet, who gives her no peace. She is still attempting to fill in the gaping hole, the scar from that devastating impact, the gaping expanse between the Americas and the Pacific Rim - the broad Pacific Ocean.