The early sun wasn’t bright enough to keep the earth warm enough to sustain life. A new model offers a solution for this old puzzle known as the “faint young sun paradox”:
A thick fractal haze of organic material helped the earth to absorb the suns warmth while at the same time blocking harmful ultraviolet light. If you looked up that ancient sky it wouldn’t be blue as today but apear only dim and rust coloured.
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Recent observations show that Plutos atmosphere shows a very similar fractal haze.