I don't think this is that controversial or hard to believe. That long ago the solar system would have been full of a lot of bodies of matter, slowly colliding

I don't think this is that controversial or hard to believe. That long ago the solar system would have been full of a lot of bodies of matter, slowly colliding, combining and growing. Eventually the bodies would grow until they formed their own orbits and there was nothing significant left to collide with. We still absorb meteorites from time to time.