
I believe her audience is those who share the same love for the beach as she does. She sees the sea and the land coming together as a representation of how adaptable we are as a human race for being able to live in such an ever-changing environment. The theme of how this kind of connection in nature can be found in so many other elements of life is kept throughout the essay. Because of this, it is easy to see how Carson keeps a running metaphor as the main purpose of her essay (which is interestingly spelled out at the end rather than the beginning). She says, "there is a common thread that links these scenes and memories--the spectacle of life in all its varied manifestations as it has appeared, evolved, and sometimes died out" (Carson 219). I found her purpose to be very similar to the idea behind string theory, again pertaining to the philosophical tone.
Personally, I think Carson's essay has done a beautiful job of combining philosophy, science and nature into one description of the mundane thing that is a beach. She uses her great talent as a writer to highlight the beauties of such a thing that we might otherwise miss when put in this type of environment.