'Green, red, even purple': The true colors of Earth’s past and future oceans
Produced by: Manoj Kumar
Green Seas
New research suggests Earth’s early oceans were not blue—but green. Rich in iron and glowing with microbial life, they looked nothing like the oceans we know today.
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Iron Flow
Volcanoes and rain-fed rivers once delivered loads of iron to ancient seas. Before oxygen, this iron shaped the ocean’s chemistry—and its color.
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No Oxygen
In the Archaean eon, Earth’s oceans were anoxic. Life thrived without oxygen, and the sky was likely orange or hazy—not blue.
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Photosynthesis Sparks
Primitive organisms using sunlight and iron—not water—kickstarted oxygen production. That shift would later change everything.
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Aurora Waters
Modern green seas around Iwo Jima reflect this ancient past. Algae bloom in iron-rich, emerald waters—mirroring Earth's first oceans.
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Pigment Edge
Early blue-green algae evolved two pigments—one for white light, one for green. It gave them an edge in the evolving color of ancient seas.
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Color Signals
If we spotted a pale-green ocean from space, it might mean early photosynthesis is underway. A visual clue to alien life.
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Future Shifts
As the sun brightens and oxygen vanishes again, Earth’s oceans could turn purple, red, or even brown—life shifting in color once more.
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Nothing Lasts
Oceans, like the sky, are not forever blue. On geological timescales, sea color is a signal—a shifting story of life, light, and deep time.
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