Off the top of your head, can you name the four spheres of Earth? If it’s not coming to you easily, a group of Flagstaff 5th graders can help. The students at Killip Elementary School are studying Earth’s biosphere, geosphere, atmosphere and hydrosphere. Its’ part of a special STEM program to help kids apply real world observations to their school work. On a recent trip to Lake Mary, they worked with scientists and field experts to see Earth’s spheres in action. Arizona Public Radio’s Justin Regan has this audio postcard.