When There Was No Oxygen on Earth the Oceans Were Green. Scientists Claim It Could Change to Purple Next
There are certain things that have become mainstays on Earth. One of these things is the ocean being blue, there are kindergarten rhymes about this fact and popular songs written on this topic. However, a recent study has claimed that the oceans' being blue was not a reality for the whole of Earth's existence, stated Live Science. The claim was explained in detail in Nature Ecology & Evolution.
The study claims that the oceans were green during the Archaean eon. This period began four billion years ago and ended 2.5 billion years ago, according to the University of California Museum of Paleontology. As per findings, the atmosphere was quite distinct from present-day conditions, and the first forms of life also appeared on the planet during this period. This implies that the atmosphere then, though different, could support life. This means that the ocean color, if different, could still act as a habitat for several beings.
The team began their examination after noticing that the waters surrounding the Japanese volcanic island of Iwo Jima were greenish. This color typically facilitates due to the presence of oxidized iron - Fe(III), as per experts. This implies that this element is also present in the water. Researchers further noted that these waters had a high population of cyanobacteria. The ancestors of this group of bacteria also reportedly thrived in these waters during the Archaean eon.
Past findings indicated that cyanobacteria performed oxygenic photosynthesis amidst the Great Oxidation Event some 2.4 billion years ago. In this process, they used sunlight to produce oxygen and ultimately created conditions leading to the development of oxygen-dependent life forms. Early cyanobacteria used both chlorophyll and phycobilins to capture light. Researchers trying to understand how these organisms evolved to use both pigments formulated several advanced simulations. These simulations helped the team in understanding how these beings evolved in waters, what conditions they found suitable, and so on.
The simulations indicated that during the Archean eon, which kickstarted 2.5 billion years ago, the water must have been green. The color was a consequence of iron precipitation. Researchers detected that at that time, the water had high amounts of ferrous iron released from hydrothermal vents. Experts further claimed that the iron-rich particles absorbed red and blue light and allowed the green light to be transmitted. "Genetic analysis revealed that cyanobacteria had a specialized phycobilin protein called phycoerythrin that efficiently absorbed green light," said Taro Matsuo, the lead author of the study, stated SciTech Daily. "We believe that this adaptation allowed them to thrive in the iron-rich, green oceans." Hence, wherever the cyanobacteria existed in the Archaean eon, the water was possibly green.
During the Great Oxidation Event, the increase in oxygen changed the ferrous to ferric iron. After the event, the iron levels dropped and oxygen levels increased, as per experts, stated Earth. This reduced the transmission of green light in the ocean. Hence, the water turned back to blue. Cyanobacteria also, by then, had evolved so much, especially on land, that they did not need to absorb green light for survival. Though in multiple underwater habitats, the organism continues to absorb the particular light for photosynthesis.
The team believes that their examination showcases that the color of the ocean depends on the chemicals present in its waters. If more volcanic activities take place on Earth, with a steady decline of oxygen in the atmosphere, there is a possibility that oceans can turn purple, according to experts. This would be because of an increase in the number of purple sulphur bacteria.