Interesting New Scientist article about how things would go if humans suddenly vanished: vines smothering the skyscrapers like in a Batman comic, highways overgrown, wheatbelt and other monocultures reclaimed over many decades while suburbia is swallowed more quickly, unmaintained reactors going critical, CO₂ levelling off at an artificial level for a while before the ocean mops it all up on the timescale of centuries - all very evocative. I wonder about toilets: will our porcelain outlast our concrete in the same way that pottery shards and tiles turn up in archaeological digs? Will aliens rummaging in our ruins ponder the meaning of the puzzling phrase "Armitage Shanks"?
One logical glitch in the article says,

If another intelligent species ever evolves on the Earth - and that is by no means certain, given how long life flourished before we came along - it may well have no inkling that we were ever here save for a few peculiar fossils and ossified relics.

Um, after 3000 words telling us how traces of our mighty civilization will vanish after only tens of thousands of years and only some odd geochemistry and an expanding front of radio waves to comemmorate us on a longer timescale, you probably ought not to venture an opinion about what might have happened here on Earth three billion years ago. That's all I'm saying.