Listening practice: The sky shield that is healing

Before sunrise over Antarctica, a strange blue and purple map can appear on a scientist's screen. It does not show land, ocean, or temperature. It shows the amount of ozone high above the planet. According to NASA's Ozone Watch, satellites help monitor this thin protective gas, and the darkest colors can mark places where ozone is unusually low. The story behind that map begins with something you cannot see, but your skin, your eyes, crops, and tiny ocean life all depend on it.