Hour Two, "Origins: How Life Began," zeroes in on the mystery of exactly how it happened. Join the hunt for hardy microbes that flourish in the most unlikely places: inside rocks in a mine shaft two miles down, inside a cave dripping with acid as strong as a car battery's, and in noxious gas bubbles erupting from the Pacific ocean floor. The survival of these tough microorganisms suggests they may be related to the planet's first primitive life forms. Tyson deepens the search by investigating tantalizing and controversial chemical "signatures" of life inside three-billion-year-old rocks and meteorites found around the world.