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When viewed from space, Earth appears blue (water) with bits of green (land with plants on it). However, one scientist posits that the Earth may have been purple a long time ago, thanks to ancient microbes that obtained energy from the sun using retinal rather than chlorophyll, the pigment which makes plants appear green.
Since retinal absorbs the green light that makes up most of the sun's energy and reflects back violet and red light, the combination would have given the planet a purple tint.
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