Scientists believe that in the early stages of the development of earthly life, our planet was not green, but purple.
There was not always as much oxygen in the Earth's atmosphere as it is now. In the early stages of the planet's development, earth's air consisted mainly of carbon dioxide and methane. The balance in favor of O2 changed about 2.4 billion years ago. The reason for this was cyanobacteria, which displayed the ability to photosynthesize. By absorbing carbon dioxide and absorbing solar energy, they emit oxygen intensively.
Photosynthetic life forms were on Earth even before the "oxygen catastrophe", but how they evolved and came to use chlorophyll is not known. Chlorophyll is the main pigment in photosynthesis that captures the energy of sunlight - ed.). American scientists Shiladitya Dassarma and Edward Schweiterman suggested that retinal was the main photosynthetic pigment before chlorophyll.
Unlike chlorophyll, which absorbs light in the blue and partly red range, retinal “catches” the green part of the spectrum. It is part of bacteriorhodopsin, with which some bacteria carry out photosynthesis. It gives the colonies of microorganisms a purple-red color.
The assumption of scientists is very important for understanding the evolution of terrestrial life, but also for the search for extraterrestrial civilizations. The Earth is often referred to as the "green planet", but it had a "purple phase". In addition, if there are photosynthetic life forms on any exoplanet, they probably use retinol: it is simpler than chlorophyll and clearly should be more common in the Universe.
