yes i agree there are billions of other galaxies which means there must be another planet similar to earth somewhere in one of them galaxies, meaning life could have evolved elsewhere.

The problem facing us though is that the solar system seems to be moving away from each other as we can see by the redshift on the spectrum, similar actions to what happened to Pangaea on earth.

This means reaching other life forms is becoming more and more difficult.

I do not believe aliens have visited this earth due to my comment above but what i do believe that there was once living organisms on Mars, due to the water found beneath the rock (frozen) and the fossils.

Aliens do not need to breathe oxygen, they could breathe any type of gas or maybe not even breathe at all.

The only time we may come close to visiting aliens or other life forms is when our galaxy collides with another (which is predicted to happen) but the sun is to burn out into a black dwarf before then, and even if we do collide with a galaxy beforehand we may not expand but become a black hole, leaving us, either way with nothing .