earth
Planet earth is the only planet that we know of that has life on it.
The only known planet to support life as we know it is the one you and I are on, Earth.
Because it is the only planet that we know of having a atmosphere
At the moment, as far as we know, the only planet suitable to support a diversity of life is our Earth.
So far the answer is Earth... But we are still looking around...
Earth is the only one we know about.
It is the only planet that supports life. (As far as we know)
Currently, we do not know of any life that exists within the Andromeda galaxy. Our planet is the only place we know that has life on it.
As far as we currently know, it is Earth. But earth may in fact not be the only planet able to harbor life. We have just begun looking.
So far, Earth is the only planet we know of that has intelligent life.
We need to live on it! It is the only planet, that we know will sustain life.
Earth is the only planet which is known to harbour life.