Without sand, engineering would be stuck in the Middle Ages. Wooden houses would line mud-packed streets, and Silicon Valley would be, well, just a valley. Sand is the building material of modern cities, and we use more of this resource than any other except water and air. Now we’re running out of it.  Hear why the Roman recipe for making concrete was lost until the 19th century, and about the super-secret mine in North Carolina that makes your smartphone possible.  Plus, engineered sand turns stormwater into drinking water, and why you might think twice about running barefoot on some tropical beaches once you learn about their biological source. And, a special report from the coast of Louisiana where livelihoods and ecosystems depend on the successful release of Mississippi sand from levees into sediment-starved wetlands. Guests: Vince Beiser – Journalist and author of “The World in a Grain: The Story of Sand and How it Transformed Civilization” Joe Charbonnet – Science and policy associate at the Green Science Policy Institute in Berkeley, California Pupa Gilbert – Biophysicist and geobiologist, University of Wisconsin, Madison Rudy Simoneaux – Engineer manager, Coastal Protection and Restoration Authority, Baton Rouge, Louisiana Elizabeth Chamberlain – Post-doctoral researcher in Earth and Environmental Sciences, Vanderbilt University Learn more about your ad choices. Visit megaphone.fm/adchoices