The people in this northern Myanmar forest have lost a way of life that goes back generations. But if they complain, they, too, face the threat of death. This forest is the source of several key metallic elements known as rare earths, often called the vitamins of the modern world. Rare earths now reach into the lives of almost everyone on the planet, turning up in everything from hard drives and cellphones to elevators and trains. They are especially vital to the fast-growing field of green energy, feeding wind turbines and electric car engines. And they end up in the...