Alien composition

If the big bang were true, and the world started as a little pile of space rocks, getting gravitation under control. Become bigger and bigger, getting blow after blow from more space debris.
Adjusting to a tiny planet and still growing over the next billion years, still getting hit with debris, but to really affect the surface and surroundings, bigger rocks are the ones challenging the planet.

With all this modifications and crafting of a planet, DNA, atoms and molecules coming out of space on this rocks/debris, does that make us aliens too?

First came oxygen and water, then came life as little as we still know about it. Then there were the dinosaurs, perhaps after a few blows from an asteroid/meteorite aswell. Eventually came the asteroid or asteroids that destroyed the dinosaurs, changing the planet, bringing new molecules and DNA, making our lifes possible.

We evolved from breathing this oxygen, we created lungs? Why should it be so hard to imagine that in our own solar system, there is life evolved to their own surroundings, like fish did below the water surface on our very own globe of alien composition!