There is an article on The Atlantic about a couple of NASA scientists considering the question of pre-human civilisations on Earth. If it was short lived how would we tell it had been there? What would we be looking for anyway?

Naturally, this hypothesis takes its name from Doctor Whoโ€™s misnamed homo reptilia. Activate your lizard brain now and join the hunt.

The Silurian Hypothesis: Would it be possible to detect an industrial civilization in the geological record?