Once upon a time when the Earth’s atmosphere was not yet enriched with oxygen, the oceans took on a green color, and that was the beginning of a tremendous change. According to Japanese scientists, this may happen again. Moreover, the hydrosphere of our planet may also become purple or red.
Green color of the Earth’s oceans
Earth is a planet that looks bluish-green from space, with the former color clearly dominant. The reason for this is that almost three quarters of our world’s surface is covered by oceans of exactly this color. However, this was not so recent, a group of Japanese scientists published a paper suggesting that this situation could happen again.
The key to everything is biochemistry. It happens that modern algae grow so much that entire bodies of water turn green. But on the scale of oceans, this never happens, and ponds are very rarely completely green, except when we can visually see plants covering their surface.
The reason for this is modern photosynthesis, which occurs in an aerobic environment. Microscopic algae need oxygen to be present in the water and when they become abundant, they simply die and instead of green, the water turns brown.
However, there is another kind of photosynthesis that does not require oxygen. And 3.8-1.8 billion years ago, conditions were conducive to it. There was almost no oxygen in the atmosphere and oceans. But dissolved iron was abundant. It enabled cyanobacteria, also called blue-green algae, to photosynthesize, and they did it for energy, and oxygen was at first a toxic byproduct.
In anaerobic photosynthesis, cyanobacteria did not need oxygen in the water. Therefore, their concentration could be much higher. That’s why water in those times could acquire a really rich green color.
Great oxidation event and future color of the ocean
Gradually, there was more and more oxygen in the atmosphere and ocean. This was happening in waves. Scientists know this because of the iron. It was always precipitating and forming future deposits. And their color is very different depending on whether it happened in the presence of oxygen or without it.
Ironstones of Precambrian time have a striated structure, indicating fluctuations in oxygen levels. But eventually the environment got saturated with it, the unfit organisms died out, and the world became as we know it.
However, it is quite possible that the green color of the oceans will still return. At least Japanese scientists are studying iron-laden waters near Iwo Jima Island. Cyanobacteria still thrive there. But when researchers genetically altered them so that they were adapted to anaerobic photosynthesis, it turned out that they became even more adapted to the native environment.
Therefore, if conditions on Earth change in the future and there is more oxygen in the atmosphere, the ocean waters could become green again. In addition, they can also turn purple in case of excessive sulfur or red if algae of that color start breeding in them, which also exist.
According to phys.org
