Through the process of photosynthesis, plants, algae, and bacteria use sunlight to convert water and carbon dioxide into the oxygen and food that sustain much of life on Earth. This Cribsheet covers the basics of photosynthesis: where it happens, how light is used in the process, and why we think photosynthesis may have triggered the rise of complex life. In addition, we tell you why plants are green and how photosynthesis could temper climate change—if rainforests and oceanic ecosystems aren’t destroyed.