'The Earth After Us' is an interesting scenario about an intelligent alien species finally encountering Planet Earth in one hundred million years time and examines how they would use scientific methods and reasoning to explore the history of the planet and, in particular, any trails of evidence of human activity.
The book is well written and researched by a knowledgeable author and educator, however it's not oriented to the layman (although it is rather quirky in places). Suffice to say that some higher education background study of geography or geology would be a definite asset when going through this.
One overarching feature of the book is how humans have impacted upon earth within a very short period of time and how old the planet really is (compared to the short human experience here). You're also reminded about how comparatively insignificant our existencies are in the grand scheme of things (even the shape of the continents will look radically different in one hundred million years).
Overall, this is an interesting and worthwhile read, but if you're looking for a book about how the earth will gradually evolve when humans have gone (and the evidence they'll leave behind) in a much shorter timeframe then you would probably enjoy 'The World Without Us' by Alan Weisman.