Were Our Blue Oceans Once Green?

Eddie Gonzales Jr. – MessageToEagle.com – Scientists find evidence that our oceans used to be green, suggesting that this may be a sign of primitive life, including that on alien worlds.

The photo was taken by our research team on Iwo Island in the Satsunan Archipelago, Kyushu, in 2023. We measured the underwater transmission spectrum, iron oxide concentration, and the cyanobacterial species present. Credit: Taro Matsuo

Imagine the world’s oceans with their beautiful blue color. Now, imagine that the same oceans were green. This is the intriguing possibility suggested by new research from Nagoya University in Japan. A group led by Taro Matsuo has found evidence that cyanobacteria, important bacteria in the evolutionary process, flourished in green seas.

Their discoveries suggest how different the world was 2.4 billion years ago during a period called the Great Oxidation Event. This event was triggered by cyanobacteria performing oxygenic photosynthesis for the first time, which used the energy from the sun and released oxygen. Over time, this oxygen accumulated in the atmosphere, dramatically transforming Earth’s environment and paving the way for the emergence of our oxygen-breathing ancestors.

In the modern world, most oxidation is performed by plants, using chlorophylls. However, the ancient cyanobacteria also used additional pigments called phycobilins, which were an integral part of their light-harvesting antennas. The researchers became interested in the question of why cyanobacteria required phycobilins in addition to chlorophylls.

Using advanced simulations, they found that the underwater light spectrum during the Archaean era (4–2.5 billion years ago) changed to green due to iron precipitation. At the time, the Earth’s oceans contained high levels of ferrous iron, which was released by hydrothermal vent systems. The Great Oxidation Event changed this balance, as the oxygen reacted with the iron, changing it from ferrous to ferric iron.

Ferric iron has different properties, such as being insoluble, causing it to precipitate out as rust-like particles. The presence of these iron-rich particles changed the wavelengths of light that could penetrate the water. As the particles preferentially absorbed blue and red light, mainly green light was transmitted, causing the underwater environment to be dominated by green hues.

“Genetic analysis revealed that cyanobacteria had a specialized phycobilin protein called phycoerythrin that efficiently absorbed green light,” Matsuo said. “We believe that this adaptation allowed them to thrive in the iron-rich, green oceans.”

Could we be looking for the wrong signs of alien life?

Matsuo also believes his research may help in the search for life in outer space. On Earth, the ocean appears blue because water absorbs red light and scatters blue; however, the green oceans in the Archean era might have efficiently reflected green light due to iron precipitation. Therefore, looking for green oceans could be used as a sign of primitive life on distant planets.

Matsuo is excited about the possibility of green oceans improving the search for alien life. “Remote-sensing data show that waters rich in iron hydroxide, such as those around Iwo Island in the Satsunan archipelago, appear noticeably brighter than typical blue oceans,” Matsuo said. “This leads us to think that green oceans might be observable from a longer distance, making them easier to detect.”

The green ocean hypothesis

The research shows the intricate balance between the surface environment of the Earth and photosynthetic organisms. The findings suggest that the emergence of photosynthetic life led to environmental changes, which in turn fostered further evolution of photosynthetic organisms, showing how life and the Earth often coevolve.

Matsuo is convinced that the green ocean hypothesis brings together findings about the Earth in its early stages. “When I first had the idea that the oceans used to be green, back in 2021, I was more skeptical than anything else,” he said. “But now, after years of research, as geological and biological insights gradually came together like pieces of a puzzle, my skepticism has turned into conviction.”

“For me personally, a major turning point was our field survey on Iwo Island in the Satsunan archipelago in 2023,” he added. “From the boat, we could see that the surrounding waters had a distinct green shimmer due to iron hydroxides, exactly like how I imagined the Earth used to look.”

Source – Nagoya University via Eurekalert

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Written by Eddie Gonzales  Jr. – MessageToEagle.com Staff Writer