What does a world of 7 billion people look like?

Today saw the world's human population pass 7 billion for the first time ever — it's a huge landmark that's almost impossible for our limited brains to encompass. Luckily, National Geographic has been doing a year-long series about the growing population, and they've gathered some of their most arresting images, video… »10/31/11 8:30pm10/31/11 8:30pm