for "our changing planet," i'm jane joyce.learn more about our changing planet, visit us on the web at. . .

-rock] ♪ ♪ (jane joyce) floating near the sunlit surface of earth's oceans, billions of tiny organismsled phytoplankton are the base of the food pyramid for all life. they also shape global climate. from space, different colors of ocean water reveal different concentrations of phytoplankton. phytoplankton play a critical role in balancing the amount of carbon dioxide in the atmosphere. during photosynthesis, phytoplankton capture water from their surroundings, carbon dioxide from the air, and energy from the sun to build plant material, the primary food source for aquatic life. while most phytoplankton are eaten by other tiny organisms and fish, some of them sink, and are eventually buried under sediment for centuries. in this way, phytoplankton extract nearly half of the atmosphere's carbon dioxide that otherwise would trap the sun's energy and warm the planet. phytoplankton also generate as a by-product more than half of the oxygen we breathe. for the first 2-billion years, earth's atmosphere lacked oxygen. phytoplankton patiently reengineered the atmosphere to where it now has 21% o