Produced by: Manoj Kumar
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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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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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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Primitive organisms using sunlight and iron—not water—kickstarted oxygen production. That shift would later change everything.
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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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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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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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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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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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