Jan Zalasiewicz is a geologist active at the University of Leicester. His 2008 book The Earth After Us: What Legacy Will Humans Leave in the Rocks? is an interesting read even though the title does not correspond very well to the contents. Zalasiewicz does answer the question about what legacy humans will leave in the rocks. But on their own, these answers would only provide material for a magazine article. The bulk of the book is instead an introduction to geology which allows the neophyte to understand what will happen to the remains of today’s world as millions of years pass.
Having no geological training, I learned a lot from the book. An idea that I found particularly interesting was that sedimentary strata show a periodicity linked to the Earth’s movement through the solar system, the Milankovitch cycles. Another was that palaeontology’s source material is partly determined by what rocks happen to be currently available for inspection at the surface. Another was that anything that spends a lot of time at the surface of the Earth will soon erode away, which means that a few million years from now it will be impossible to study humanity’s hominid ancestry. Highland ecologies rarely fossilise.
But to me, the book’s take-home message is that humanity’s reign on Earth will mainly show up in the palaeontological record not as a stratum, but as an interface between geological periods. Such a period interface is defined as a place in a stratigraphic column where ecology shifts dramatically, many species go extinct and new ones evolve in their place. Zalasiewicz is quietly convinced that we are a blip on the timeline, with no chance whatsoever of sustaining our great numbers and high technology for more than another few centuries. To future geology, the heyday of Homo sapiens will just be one of several instantaneous mass extinction events in the planet’s history.
See also my review of Alan Weisman’s 2007 book The World Without Us.