Ancient Oceans May Have Been Green, Not Blue, Due to Cyanobacteria

Oceans on Earth may have appeared green billions of years ago, according to new research. Scientists suggest that ancient oceans were filled with cyanobacteria, a type of microbe, which affected how light was filtered through the water. Unlike today's oceans, which appear blue due to the absorption of red and yellow light, the presence of cyanobacteria would have caused the water to absorb green light, giving the oceans a green hue. This is because cyanobacteria contain chlorophyll, which absorbs red and blue light but reflects green light. Researchers created models that took into account ocean chemistry, light diffusion, and pigment absorption. The models showed that in depths of 5 to 20 meters, the ancient oceans would have consistently appeared green. This finding challenges traditional assumptions about the appearance of early Earth and suggests that the presence of green oceans could be a sign of microbial life on other planets.