Examining Earth's complex atmosphere. Included: how it is necessary for life on the surface; a man who braved its dangerous upper reaches and survived.

On a single day on a single street, with the DNA of just a couple of hundred random people, National Geographic Channel sets out to trace the ancestral footsteps of all humanity. Narrated by Kevin Bacon, The Human Family Tree travels to one of the most diverse corners of the world -- Queens, N.Y. -- to demonstrate how we all share common ancestors who embarked on very different journeys. Regardless of race, nationality or religion, all of us can trace our ancient origin back to the cradle of humanity, East Africa. What did our collective journey look like, and where did it take your specific ancestors? At what point in our past did we first cross paths with the supposed strangers living in our neighborhood? Now, in The Human Family Tree, the people of this quintessential American melting pot find out that their connections go much deeper than a common ZIP code.