Is "our" earth the only earth out there? ~

It had better be, as we've copyrighted the name "earth".  If someone else out there is calling their place "earth" we're going to prosecute.

I hope your not planning to dish the dirt elsewhere ....:( 

It’s the only earth we know. I would find it difficult to not believe way out there somewhere there’s not a comparable planet and solar system. 

There's only one "Earth" - anything anywhere else comparable would have its own-languages name for it!

More to the point, we cannot and probably will never, know; but there is no reason to think other Earth-like planets cannot or do not exist.   We must be careful though, not to fall for the old science-fiction writers' self-deprecatory habit of imagining any other civilisation out there is vastly more advanced than our own.

(Some might argue our own civilisation is not particularly civilised anyway... but we don't want our domestic arguments splashed around the galaxy, now, do we?)

Any other society might be far more developed than ours... or it might be far behind. We won't know, because the sheer scale of Space and the simplest laws of the Physics that operate it, bar any sort of examination or communication.

i dont think we'll ever know

I doubt it--nature seems to like playing with particles to build molecules to make various substances which may result in creating a  molecule that enables life to begin wherever/whenever conditions are suitable. This post was edited by Kittigate at September 9, 2018 11:51 AM MDT

I agree it is very much a matter of chance, and that of life very similar to that on Earth perhaps even lower; but I don't rule out the chance of life of some sort, somewhere. As Pearl says though, we'll probably never know.

Astronomers have already given letter-digit code-names to those that they've found within the range of our telescopes within our own galaxy, the Milky Way.
To qualify, the planet must be the right distance from a G2 type star, with the right orbit, axial tilt.
What we don't know is how many of them also have liquid water and the right atmosphere in order to make the preconditions for life possible.

Since there are so many within the range of our telescopes, it is assumed that there is an uncountably large number of such beyond the range of current ability to detect them. From this, it is guessed that it would be highly unlikely for other forms of life not to have evolved elsewhere.
When scientists talk of life, they don't necessarily mean life like our own. It could be anything from the rudiments of the proteins that make up RNA and DNA - to life-forms that have evolved in ways that we cannot imagine. Bio-chemistry and bio-mechanics would cause similarities in functions - but the forms could be infinitely variable.

However, even the closest possibly inhabitable planet is four light-years away - and no one has yet worked out a way to travel at just under the speed of light.

Terrestrial exoplanets exist by the trillion - but the series of unlikely events thst made intelligent life possible on this one are of the "there ain't no such animal" variety. Possible, certainly - but certainly not in the abundance sf writers would have us believe.