A recent study suggests that Earth's oceans may have appeared green billions of years ago during the Archean eon (3.8 to 2.5 billion years ago). This contrasts with the modern view of Earth as a 'pale blue dot'. The hypothesis is based on the chemistry of ancient oceans and the evolution of early photosynthetic organisms.
During the Archean eon, Earth's oceans contained high levels of dissolved iron. These iron-rich waters absorbed red and blue light, reflecting green light. Cyanobacteria, early photosynthetic organisms, thrived in these conditions, utilizing pigments called phycobilins to capture green light. As cyanobacteria flourished, they released oxygen through photosynthesis, leading to the oxidation of iron and a shift towards the blue oceans we see today.
Researchers suggest that the presence of green oceans could be a sign of early life on other planets. The study highlights the connection between ocean color, water chemistry, and the influence of life, offering insights into the evolution of life on Earth and the potential for life beyond our planet.