What will remain of us hundreds of millions of years from now? And how can we be so certain that we are the first technologically advanced species on Earth?

These unsettling questions have been haunting listener Steve. If fossils can be lost to deep time through erosion and subduction into the Earth’s mantle, how would anyone — or anything — ever know that we had been here? And if an earlier species had built a civilization that rose and fell, would we even be able to find traces of it?

To investigate, CrowdScience presenter Caroline Steel speaks to the scientists trying to answer these questions, while producer Sam Baker goes fossil hunting on the Jurassic Coast in the UK.

Caroline speaks with astrophysicist Adam Frank at the University of Rochester in the US, who along with NASA scientist Gavin Schmidt developed the Silurian hypothesis – the idea that if an advanced species had existed deep in Earth’s past, they might have vanished without leaving a trace.

But palaeontologists Jan Zalasiewicz and Sarah Gabbott from the University of Leicester in the UK argue that humans are already leaving an indelible mark in the form the chemical and material fingerprints we’re pressing into Earth’s crust. They contend that the ‘technofossils’ we are producing will last a very long time indeed.

Along the way, Caroline and producer Sam discover just how rare fossils really are, how even the tiniest particles of pollution will give us away to far-future explorers, and why car parks might be our ultimate legacy. What they find is at once unsettling and oddly comforting: humanity could be fleeting, but our impact probably won’t be.

Could we really have missed evidence of an ancient civilization? And what strange clues will we leave behind for whoever, or whatever, comes next? We explore Earth’s geological memory to find out.

Presenter: Caroline Steel Producer: Sam Baker Editor: Ben Motley

(Photo: Old phone embedded in concrete layer with defocused landscape background Credit: Petra Richli Via Getty Images)