The Sky Wasn’t Always Blue

The color of Earth’s sky has changed over time due to the presence and activities of different life forms. Initially, the sky had a grayish-blue-green tint due to a nitrogen and carbon-dioxide-rich atmosphere with little oxygen. Methanogenic bacteria then turned the sky orange by producing methane, which formed hazes that absorbed blue light. Eventually, cyanobacteria produced oxygen, which cleared the haze and restored the sky to its current blue color.