The United Nations says today symbolically marks the moment when the world’s population reaches 7 billion. A little more than two centuries ago, the global population was 1 billion. How did it grow so big so fast? With the help of a sound montage and video, it gets a little easier to see how the Earth can produce that kind of a crowd.
Watch our video: 7 Billion: How Did We Get So Big So Fast
Photo: Adam Cole, Maggie Starbard / NPR