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If advanced civilisations had already lived on Earth, would they have left a trace? Astrobiologist Adam Frank and climatologist Gavin Schmidt philosophise about the evidence we humans might leave behind in the Earth’s geological record millions of years after we’ve gone extinct. They start by speculating whether a fictional advanced race of lizard-like people – the Silurians, from Dr. Who – would leave any clues.

Picture: Silurian Warriors, Credit: ÃÛÑ¿´«Ã½