@camlok,
Think of a plateau rather than an apex. You can't really talk of a single most important invention, because there are many that have been equally important to civilization. I think it would help to keep that in mind when answering this question. Still, it's a good post.
James Burks book, "The Day The Universe Changed" is a good book on the subject. It's about how inventions and discoveries changed the course of history.