It may not appear very lively six feet underground, but a single teaspoon of soil contains more organisms than there are human beings on the planet. From bacteria and algae to fungi and protozoa, soils are home to one quarter of Earth’s biodiversity. And perhaps soil’s most important inhabitants are its microbes. Carolyn Marshall digs into how soil’s invisible helpers support all life on Earth. [Directed by Ivana Bošnjak and Thomas Johnson, narrated by Alexandra Panzer, music by Stephen LaRosa].