How is it possible to know that we exist?

"Exist" should not even be in a biological machine's vocabulary. Think about it (if you can keep from going crazy). We are the pointless results of billions of years of celestial evolution, here for nothing and from nothing. And nothing doesnt care if we survive, or make babies, or even not exist at all. So why do we care? Why do we have awareness? We are only "aware" of what our nervous system clues us in on in the first place. There is so much we can't know. Or even if what we do know is real, anyways. Like this whole "existence" thing. It don't matter to the big picture. Not that the big picture could care, because the big picture isn't conscious anyways. But we are. The chair isnt, the sun isn't, even the universe itself isn't, but we are. How?