I think humans got on this Earth via evolution of other organisms which evolved from tiny single-celled water inhabiting creatures that got here from a meteor crash on Earth. I think this because it is impossible to create something from nothing. I think that somewhere along the line there was a “supreme being”, call him God, the Creator, the concept is similar. I think that then a meteor came from another, far away place and hit Earth.
Although the chances of collision on Earth being slim, in my mind I cannot see any other way of organisms coming to Earth without any other interference from other intelligent races. Although interference may be possible, the intelligent race must also have come from somewhere, which could also have originated from a meteor crash. I think then the species that hit Earth adapted to the environment and evolved, and over billions of years evolved to become humans.
Chances of other races existing somewhere in the universe are incredibly high. We have only seen a percentage of a percentage of the universe, and we are here. Somewhere in the universe there must also be intelligent races.