It's the ultimate city, packed with 8 million people and overgrown with skyscrapers. But before this land of glass steel and concrete sprouted, New York City was home to alien worlds and strange creatures stretching back over many millennia. Eight-ton elephant-like mastodons walked down what is today 5th Avenue, and a sea turtle bigger than a compact car swam directly over Midtown Manhattan. The Big Apple still bears the scars of a time when it was obliterated by a titanic glacier, and it sits on the site of a 200-million year old volcanic catastrophe. This is also where some of the world's first dinosaurs walked. And although it enjoys views of the Atlantic Ocean today, New York City was once in the middle of a vast desert continent. No matter the era, it's been the center of the action throughout the history of our planet.