What main theme do all of the pieces within Notes from an Apocalypse revolve?

All of the pieces within O'Connell's book focus on the phenomenon of the end of the world. By exploring the topic through the lens of space exploration, political reckonings, and a variety of other elements, O'Connell attempts to investigate what it means to live in a world with a shelf life, particularly when that ending will have been brought on by our own careless actions.