We are, as far as we know, unique.
Through sheer probability, an entire universe exploded into being where previously nothing existed, and through an almost 14 billion year process of explosion and condensation, produced stars, asteroids, comets, planets, moons, and eventually us.
There is no known big-picture purpose for our existence. Random chance is all that is responsible for our being here roughly 80 years each. Knowing this, we spend our time here working to create, to experience, and to love. Our actions are a contribution; all our efforts serve to ensure that people who live after us have the same opportunity to experience life, whatever it may mean to each of them. This is our obligation. We are shepherds of this world.
When the time comes that we must die, there is nothing to fear or be sad about. Every life is a life worth living; for a brief moment in the cosmic timeline, the universe knew itself through each of us, and now we are returning home. This is the most beautiful thing I know.