New Scientist has an interesting piece on how Nature would begin to reclaim the planet if all humans were spirited away tomorrow.
Fields and pastures would revert to prairies and forest, the air and water would cleanse themselves of pollutants, and roads and cities would crumble back to dust.
Says author Bob Holmes:
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.
Yet if future observers have good enough scientific tools, they could still find a few hints of our presence, such as:
- the fossil record would show a mass extinction centered on the present day and dense concentrations of skeletons of a large bipedal ape
- today's landfill sites will still have fragments of glass and plastic, and maybe even paper
- ocean sediment cores will show a brief period during which massive amounts of heavy metals such as mercury were deposited, and a concentration of radioactive isotopes left by reactor meltdowns
- the atmosphere will bear traces of a few gases that don't occur in nature, especially perfluorocarbons such as CF4
- finally, radio waves will forever radiate out across the galaxy and beyond.