Purple Earth hypothesis
Astrobiological hypothesis regarding early photosynthetic organisms Artist's impression of Earth in the early Archean with a purplish hydrosphere and coastal regions Purple culture of Haloarchaea (left) and isolated purple and red membrane components (right) The Purple Earth Hypothesis (PEH) is an astrobiological hypothesis, first proposed by molecular biologist Shiladitya DasSarma in 2007,[1] that the earliest photosynthetic life forms of Early Earth were based on the simpler molecule retina