A few years back someone wrote an article (to a science journal I think) asking if it was possible that the dinosaurs had high technology but all evidence of it had vanished in the millions of years that have passed.

Some dinosaurs were around for millions of years, which is a phenomenal amount of time compared to human history, and if humans go extinct anytime soon we may leave very little trace of our technology for a species 60 million years after us.

Two factors weighed against it: plant diversity and evidence on the moon.

The first comes from the argument that any sufficiently advanced civilization will travel around the globe, so fossil records will show the same plants everywhere. It's tricky to determine this but the evidence seemed against it.

The second is simply that any high technology civilization will eventually travel to the moon, which allows for a much more undisturbed record.