In a crater at the top of a dormant volcano lies a place so quiet, the ambient sound is right near the threshold of human hearing. Visitors to the crater say they can hear their own heartbeats. This spot, in Haleakalā National Park, has been nicknamed the "quietest place on Earth."Getting there is no small feat--the ascent involves hiking upward through five different climate zones. But the reward is an experience of natural silence that is increasingly difficult to find.Conservationists, park scientists, and communities all over the United States are working to conserve their pristine soundscapes while noise pollution from planes, vehicles, and other human sources increases. Today, Regina G Barber talks with producer Margaret Cirino about the history, culture, and sound of the Haleakalā crater, and why it should matter to all of us.