The planet's first photosynthesizers dined on green light
Planet Earth is blue. Most of its surface is covered in water, the vast majority of which is ocean, and water generally absorbs longer wavelengths of light, such as red and orange, and reflects back the shorter blue wavelengths. When astronauts travel into space and look back at their home, they see a blue sphere in an expanse of jet black. But the blue color we associate with Earth's oceans is a relatively recent development in the planet's evolutionary history. During the Archaean Eon, which spanned 4.0 to 2.5 billion years ago, the oceans shimmered green, according to new research, and this green light may have helped to set the stage for the rise of an ancient blue-green algae that transformed the planet. Known as cyanobacteria, that algae precipitated the Great Oxygenation Event, when oxygen came to dominate the atmosphere and the oceans, which preceded the emergence of higher order creatures in water and on land. "This research is a good example for the coevolution of Earth and life, because the surface environment and cyanobacteria affected each other," says Taro Matsuo, a space physicist at Nagoya University in Japan who led the research. "Cyanobacteria could thrive under the green environment." The new findings were published in Nature Ecology & Evolution by Matsuo and a team of space physicists, chemists, and earth scientists. The researchers began their investigation by modeling the biogeochemistry of the oceans from the Archaean Eon, a time when high levels of iron bubbled up from hydrothermal vents. At first, the iron would have…