What would happen to planet earth if the human race were to suddenly disappear forever? Would ecosystems thrive? What remnants of our industrialized world would survive? What would crumble fastest? From the ruins of ancient civilizations to present day cities devastated by natural disasters, history gives us clues to these questions and many more.
Abandoned skyscrapers would, after hundreds of years, become "vertical ecosystems" complete with birds, rodents and even plant life. One small animal might be responsible for bringing down the Hoover Dam hydroelectric plant. Swelled rivers, crumbling bridges and buildings, grizzly bears in California and herds of buffalo returning to the Great Western Plains: In a world without humans, these would be the visual hallmarks. Our cars would shrivel to piles of dust, our house pets would be overtaken by flourishing wildlife and most of the records of our human story books, photos, records would fade quickly, leaving little evidence that we ever existed.
Indoor cats will need to get outside to survive, as after munching on leftover food and drinking melt water from freezers, they will soon run out of provisions. Once outside, cats have a great chance at survival. Because they have generally retained their independent natures and are natural hunters, they will quite easily return to the wild and provide for themselves by hunting birds and rodents. They will, however, have to watch out once predators, such as bobcats, coyotes and wolves, move back into abandoned human neighborhoods.

(Life After People is a TV documentary airing on the History Channel that attempts to forecast what our planet would be like if we were gone.)