From 1998 to 2010, Sea-viewing Wide Field of View Sensor (SeaWiFS) made a simple but elegant measurement: how “green” is the Earth. That is, how much chlorophyll—the pigment that helps turn sunlight into organic energy for plants—is present in the seas and on land. Those measurements offered a window into the planet's ability to support life. The long, well-calibrated data record also gives scientists one of the best benchmarks to study the planet’s biological response to a changing environment.