Dr Zalasiewicz is a geologist/palaeontologist, but this book is for the general reader with a  basic scientific knowledge.  He takes as his starting point the idea that millions of years have passed, Homo sapiens is long extinct, and explorers arrive from a distant galaxy.  How would they reconstruct Earth's history?  A quirky beginning, because three quarters of the book is in fact a description of how human scientists have deciphered the past, from rocks and fossils in the 17th-19th centuries, to carbon-dating and astronomical research in the 20th.  There are some oddities I noticed:  the science of stratigraphy was not originated by Smith in the 18th century but by Steno in the 17th, for example.   (Smith seems genuinely to have arrived at his idea independently, but he wasn't the first.)  Again, I would have thought that the original appearance of living, unicellular organisms (which the author dismisses in a sentence) deserves at least as much discussion as the appearance of multicellulars - you couldn't have the second development without the first, after all.  Then, the last quarter of the books gathers together the themes and points already covered, and discusses what kind of traces we humans might leave to be found a million years hence.  

Despite minor reservations the book is a very interesting, well-written and informative read.  There is a  brief timeline illustrating the relationships between various Eons, Eras, Periods, Epochs and Ages, which I found most useful, as reading geological texts can be rather like reading older Russian literature,where every character has at least 3 formal names and a nickname,and can be addressed by any or all of them.  Recommended.