One of the great revolutions in human thought was the concept of "Deep Time" — the notion that the Earth and the Universe are vastly older than recorded human history, and even the origins of the human species lie long before the invention of writing. Charles Lyell, the Victorian geologist, was probably the first person to really understand the true age of the Earth, and his ideas in turn informed Charles Darwin's theories of the evolution of species.
But the first fiction writer to really grapple with the concept appears to be H.P. Lovecraft. In his novel At the Mountains of Madness he threw a crew of Antarctic explorers into a face-to-face confrontation with the original creators of life on Earth, a tentacled species called the Old Ones whose history spans not a paltry few thousand years, but close to a billion.
And once one starts looking into the history of life on Earth, the question does arise: why did it take so long for an intelligent species (us) to evolve? There's no strong reason why intelligence couldn't have appeared in some contemporary of the dinosaurs — or even a species of the Carboniferous era, as far from the dinosaurs in time as they are from us. They had brains; why didn't some species get a bigger one? (My explanation is that intelligence is simply not as inevitable or even as advantageous as we like to think. That's also my solution for the Fermi Paradox.)
The famous British TV series Doctor Who imagined intelligent reptiles from Earth's deep past, dubbed the "Silurians" because TV writers are terrible about looking things up. (There were no reptiles in the Silurian age.) They weren't bad chaps really, they just woke up from hibernation and were horrified to find their planet overrun by primates.
All good fun. Except . . .
Why are we so sure that we are the first technological civilization on Earth? In a paper for the Journal of Astrobiology, scientists Gavin Schmidt and Adam Frank tackle the question of how we might identify signs of past civilizations. We think of our cities and roads as durable things, but geology laughs at that. Over sufficiently long timescales, all artifacts get ground into dust. Schmidt and Frank identify some markers for past civilizations . . . and consider some otherwise mysterious events in Earth's prehistory which fit those markers. Hmm . . .
You can download the paper here.