We take an average of some 600 million breaths in our lifetime, and what goes on in our body each time oxygen is taken in and carbon dioxide expelled is nothing short of miraculous. "Our lungs are the lynchpin between our bodies and the outside world," writes pulmonologist Michael Stephen. And yet, we take our lungs for granted until we're incapacitated and suddenly confronted with their vital importance. Here Stephen relates the history of oxygen on Earth and the evolutionary origins of breathing, while exploring the healing power of breath and its spiritual potential.