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 and statistics into a free iPad app.

Here are some of the most amazing images from National Geographic's series on the rising world population, plus a couple of videos that will help you think about the massive numbers of your fellow humans in a new way. You can download the app at the link. [National Geographic]