No, the oceans on earth have not always been blue. A new study by Japanese researchers reveals that they were formerly … green!
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And they could even turn into purple in a distant future, according to the article published in the journal Nature.
Several billion years ago, the oceans contained a lot of dissolved iron, deposited in the absence of oxygen, brought by volcanoes and rock erosion.
At that time, the atmosphere was almost devoid of oxygen. Some bacteria therefore used iron to produce energy thanks to sunlight.
These organizations used anaerobic photosynthesis, which means that they can do photosynthesis in the absence of oxygen.
Photo d’archives / AFP
The use of iron for photosynthesis by these primitive microbes has given ocean surface water a greenish color, dominated by specific pigments such as phycoerythrobiline, capable of capturing green light.
Scientists have found a current example of this phenomenon near the volcanic island of Iwo Jima, Japan. It is still possible to observe green waters filled with current cyanobacteria which use old mechanisms.
That’s not all: depending on the climatic, geological and atmospheric transformations to come, the oceans could again change color.
According to the researchers, water could turn in purple due to sulfur, red bacteria because of iron or brown because of a strong presence of organic matter.
The study thus demonstrates the elements of the earth are constantly evolving. The color of the oceans is far from frozen and reflects the chemical state of the planet.