February 3, 2008 – Life Grows On
From "Imagine Earth Without People" in New Scientist:
“All things considered, it will only take a few tens of thousands of years at most before almost every trace of our present dominance has vanished completely. Alien visitors coming to Earth 100,000 years hence will find no obvious signs that an advanced civilisation ever lived here.”
As for the asphalt in our yard, less than 20 years.