The orange sky
Before oxygen, the air was full of methane haze
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Methanogenic archaea dominated the early biosphere, and in an oxygen-free atmosphere methane could build to hundreds of times today's level. Photochemistry converts methane into complex organic aerosols — an organic haze that both cooled the surface by blocking sunlight and shielded it from ultraviolet radiation. Isotope data from Archean sediments suggest the haze came and went in episodes. When oxygen rose, the methane was destroyed, the haze cleared, and the planet fell into its first great ice age.
For children
The sky has not always been blue. For billions of years bacteria made methane instead of oxygen, and sunlight turned that methane into a thick orange haze — much like Saturn's moon Titan today. If you had stood on the shore back then, the Sun would have looked like a reddish smudge.
Connects to
Part of Terra Saga — the story of Earth on a timeline. terrasaga.org