This article may contain affiliate links, with Hearst Magazines and Yahoo potentially earning commission. A recent study by researchers at Nagoya University in Japan examines the likelihood that early Earth had a green appearance. Due to evolutionary factors and the light spectrum available to cyanobacteria engaging in photosynthesis in the planet’s early stages, the oceans were probably much greener back then than they are today. Despite the Earth’s predominant blue color for the past 600 million years, the increasing populations of phytoplankton due to rising temperatures are causing the oceans to once again display shades of green. On September 5, 1977, as NASA’s Voyager 1 spacecraft was leaving the Solar System, it captured an iconic image known as “The Pale Blue Dot”, showing Earth floating in a sunbeam against the vastness of space. However, throughout much of its history, Earth likely appeared more green than blue. Scientists speculate that from 3 billion years ago until about 600 million years ago, as complex life was emerging, the oceans would have been notably greener. Researchers from Nagoya University delved into the reasons behind this ancient greenish tint, pinpointing cyanobacteria as the main factor. Their findings were published in the journal Nature Ecology & Evolution. The study suggests that the perception of a planet’s potential to support life should not solely rely on its blue appearance. Various elements, particularly the composition of the early oceans, influenced Earth’s overall color. In the planet’s early years, the oceans contained iron hydroxide, which absorbs blue light, while the water absorbed red light, creating a “green light window,” as explained by Taro Matsuro, the lead author of the study. Through photosynthesis, cyanobacteria absorbed red and blue light, reflecting green due to chlorophyll. These organisms also possessed pigments called phycobilins that absorbed red and green light. By modeling the light spectrum available to ancient photosynthetic life, the researchers discovered that the spectrum aligned with the light absorbed by phycobilin pigments. When reproducing the conditions of early Earth, cyanobacteria with phycobilin pigments thrived, suggesting that evolution favored their development. Matsuro mentioned that, under a modern atmosphere, the green ocean hue would have blended with the blue from Rayleigh scattering, likely creating a more bluish-green color instead of the current blue. He also suggested that the ancient ocean was probably larger than it is today.
The impact on the planet’s color would have been much more significant. Similar to how outdated fashion trends can suddenly re-emerge as popular, Earth’s oceans could potentially shift back to the green end of the color spectrum in the future, albeit using different mechanisms. A study by MIT in 2019 predicted that by the end of the century, half of the world’s oceans could turn green as phytoplankton populations increase due to global warming. Subsequently, a study in 2023 verified that 56 percent of the world’s oceans had already transitioned to a greener hue in the last two decades. Change is the only constant, a notion that holds true for the world’s oceans as well.
