Purple Earth hypothesis

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The Purple Earth hypothesis is an astrobiological hypothesis that life forms of early Earth were retinal-based rather than chlorophyll-based thus making Earth appear purple rather than green. An example of a retinal-based organism today is the photosynthetic microbes called halobacteria.[1][2]

See also[edit]


  1. ^ LiveScience.com: Early Earth Was Purple, Study Suggests Accessed May 9, 2007
  2. ^ Sparks, William B.; DasSarma, S.; Reid, I. N. "Evolutionary Competition Between Primitive Photosynthetic Systems: Existence of an early purple Earth?". Bulletin of the American Astronomical Society, Vol. 38, p.901. 

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