This one ranks high as my favorite YouTube video:
Consider the words Carl Sagan used: "a thin film of life." Exactly how thin are we talking about? I did a simple calculation and it's quite humbling.
Suppose we consider the thickness of the film of human life on Earth to range from the Dead Sea to Mount Everest (the lowest and highest point on land, respectively). That comes to 9,226 meters. The average diameter of the planet is 12,742,000 meters: a ratio of 1:1,381. In other words, if we inflated a beach ball four feet across (large by beach ball standards) and painted it, the thickness of the paint would encompass the whole of human civilizations: every monument, empire, family, and philosophy (save satellites and other space artifacts, of course). A thin film, indeed.