Contrary to the familiar blue, Earth's ancient oceans may have sported different hues, including green, violet, or even pink. These theories stem from research into the Archean period, dating back billions of years. The color variations are attributed to the unique chemical composition of the water and the presence of early photosynthetic organisms.
The Green Ocean Theory
During the Archean Eon (4 to 2.5 billion years ago), oceans were rich in dissolved iron. According to a study from Nagoya University in Japan, high levels of ferrous iron in the oceans filtered out much of the red and blue light, leaving green as the dominant color. Cyanobacteria, thriving in these conditions, evolved specialized pigments called phycobilins to efficiently absorb green light.
The Violet/Purple Ocean Hypothesis
The "Purple Earth hypothesis" suggests that early life forms may have used retinal, a simpler molecule than chlorophyll, for photosynthesis. Retinal absorbs green light and reflects red and blue, potentially giving the oceans a purple or violet appearance. These organisms could have predated the emergence of chlorophyll-based life.
The Pink Ocean Suggestion
Fossilized chlorophyll found in cyanobacteria from the Sahara Desert was dark red and purple in its concentrated form. Diluted by water, this pigment could have lent a pink hue to the early Earth's oceans. These cyanobacteria thrived over 650 million years ago, dominating Earth's oceans.
Understanding the colors of ancient oceans provides insights into the early evolution of life and the conditions that shaped our planet. These studies offer a new perspective on how life not only adapts to its environment but also actively contributes to shaping it.