Earth’s Oceans Were Once Green, Study Reveals
Recent scientific research has unveiled intriguing insights into the historical and potential future colors of Earth’s oceans. A study published in Nature Ecology & Evolution by researchers from Nagoya University suggests that during the Archaean eon (approximately 3.8 to 1.8 billion years ago), Earth’s oceans were green due to high concentrations of iron and the presence of early photosynthetic organisms like cyanobacteria.
These organisms utilized iron instead of water for photosynthesis, leading to the accumulation of oxidized iron particles that imparted a green hue to the oceans.
Could the Oceans Turn Purple Next?
Looking ahead, scientists propose that Earth’s oceans could undergo another color transformation, potentially turning purple.
This hypothesis is rooted in the “Purple Earth” theory, which posits that before the dominance of chlorophyll-based photosynthesis, early life forms relied on retinal—a simpler pigment found in certain microorganisms like halobacteria.
Retinal absorbs green light and reflects red and blue, giving oceans a purplish appearance.
The Role of Environmental Changes
Environmental factors such as increased volcanic activity and decreased oxygen levels could elevate sulfur concentrations in the oceans.
This would foster the proliferation of purple sulfur bacteria, which thrive in anoxic and sulfidic conditions.
Their abundance could gradually shift the color of the oceans toward purple.
Implications for the Search for Extraterrestrial Life
These findings not only reshape our understanding of Earth’s past but also have profound implications for astrobiology.
If retinal-based photosynthesis was once prevalent on Earth, similar processes might occur on exoplanets.
Thus, a planet’s unusual surface colors, such as purple, could serve as biosignatures when searching for life beyond our solar system.
Conclusion: A Colorful History of Life
The color of Earth’s oceans has been dynamic over geological timescales, shaped by planetary chemistry and the evolution of early life forms.
Understanding these changes not only enriches our knowledge of Earth’s history but also fuels the ongoing exploration of life in the universe.
