The ghost of Christmas yet to come

What will be left of human civilisation in the geological record 100 million years hence?Justin Rowlatt speaks to the geologist Jan Zalasiewicz of Leicester University in an extended interview, speculating on the durability of the human legacy. We may take pride in our cathedrals, technologies and feats of engineering. But what strange fragments will survive long enough for aliens visiting our planet in the distant future to discover? And will it be enough for those future geologists to figure out what caused the mass extinction we will leave behind in the fossil record?This is an extended version of an interview recorded for Justin's Geochemical History of Life on Earth, also available on the BBC World Service.Producer: Laurence Knight(Photo: Skull fossil artwork from the Modern Fossils collection by Christopher Locke. Credit: Christopher Locke/Heartless Machine)