By Sheetal Kumari | February 18, 2025
Some scientists propose that Earth was once covered in shades of purple instead of green. The idea suggests early life forms used a different molecule for photosynthesis than today’s chlorophyll.
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The Purple Earth hypothesis suggests that early single-celled organisms used retinal, a simpler molecule, instead of chlorophyll, creating a purple hue across the planet.
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NASA-backed research supports this hypothesis, with scientists like Dr. Edward Schwieterman and Shiladitya DasSarma exploring retinal’s role in early Earth life.
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Chlorophyll, the green pigment in plants, is essential for photosynthesis, helping plants convert sunlight into energy. Without it, life as we know it wouldn’t exist.
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Before chlorophyll, retinal likely powered photosynthesis on early Earth. During this period, atmospheric oxygen was scarce, but sunlight still powered purple microbes.
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Organisms like halobacterium, purple microbes, thrived in salty environments like the Great Salt Lake. They used retinal for photosynthesis, creating their vibrant hue.
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Over time, organisms evolved to use chlorophyll, leading to more efficient photosynthesis. This shift contributed to the Great Oxygenation Event, turning Earth’s surface green.
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Astrobiologists believe exoplanets could harbor life forms that use retinal, offering insights into early stages of evolution on other planets.
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Although Earth is mostly green, places like the Dead Sea still show purple hues thanks to halobacterium, demonstrating how purple life persists in extreme conditions.
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The Purple Earth hypothesis encourages scientists to seek diverse biosignatures on other planets, expanding our search for life beyond Earth and revealing unexpected paths of evolution.
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