As a non believer I often wonder about this.
I chose "life has no purpose" although only because it comes CLOSEST to my thinking, which is that life has no INHERENT purpose or meaning. There's plenty of purpose and meaning for individuals to find for themselves, but it's not externally bestowed or universally defined.
Maybe the idea of life having a purpose is a byproduct of having evolved advanced consciousness and the prefrontal cortex. Animals don't seem to worry about such things. For them it's pretty much survival. Pets are a little different since their survival is taken care of, so they can live without worrying about those things.
Life is. Rocks are. Do they have a purpose? Granted, they can be useful but to suggest that the very act of being imposes a purpose is strained. If you wish to give your life a specific purpose that is wonderful (assuming it is a benevolent purpose, of course) but it was pretty much chance that got us here. Our duration is finite. Even that rock is gonna bite it in the end.
Technically, it's to reproduce and continue the species, but that doesn't sound all that glamorous, does it? If we were to go beyond that, I'd say that life itself has no inherent meaning, but we can make our own meaning where we see fit. Writing gives meaning to my life and so does the presence of some members of my family.
I'm somewhere between procreating, no purpose, finding joy, and just a freak occurrence of cells coming together in the right way at the right time. We're here, we may as well do something good. Or I've achieved my major purpose in passing on my DNA, I'm not sure how much use I am now except as a little cog in a big machine.