An interesting though experiment from Scientific American: What would happen if humans disappeared? Although some items -- like stainless steel pots or plastic toys -- would hang in for hundreds of years, it wouldn't take long before roads and cities started deteriorating. In a place like New York, water underground would start the ball rolling.

“Many of the buildings in Manhattan are anchored to bedrock. But even if they have steel beam foundations, these structures were not designed to be waterlogged all the time. So eventually buildings would start to topple and fall. And we’re bound to have some more hurricanes hitting the East Coast as climate change gives us more extreme weather. When a building would fall, it would take down a couple of others as it went, creating a clearing. Into those clearings would blow seeds from plants, and those seeds would establish themselves in the cracks in the pavement. They would already be rooting in leaf litter anyhow, but the addition of lime from powdered concrete would create a less acidic environment for various species. A city would start to develop its own little ecosystem."

And it wouldn't include Starbucks.