I’ve been toting around 27 pounds of carbon all of my adult life. You’ve been hauling carbon too: Approximately 18 percent of your body is made of carbon atoms. All of those atoms were once in the food we ate and, before that, in the air, oceans, rocks, and other forms of life. Carbon, an element born of exploding stars, is essential for all forms of life and so it may be surprising that more than 90 percent of planet’s carbon is underground.

Even more remarkable is the discovery that life, in the form of microbes and bacteria, thrives miles beneath our feet in such abundance that its total carbon mass is up to 400 times greater than all 7.7 billion