Many scientists believe Earth’s ancient oceans were much more acidic, making it difficult for life to develop. Organic molecules struggle to form in environments with a pH lower than 7. Ocean pH is crucial for Earth’s evolution, but early ocean pH remains debated, with estimates ranging from acidic to alkaline.
Yale and Singapore scientists have created a comprehensive model to estimate the origins of Earth’s habitability, focusing on ocean acidity.
Based on Yale-led research, the new theoretical model examines various geological and atmospheric processes. It provides a clear picture of how Earth evolved to support life. This comprehensive model bridges the gap between surface and deep Earth processes, offering the most detailed estimate of how ocean pH changed throughout Earth’s history.
pH, or “potential of hydrogen,” measures the concentration of hydrogen ions in a watery solution. Lower pH means higher acidity. Solutions with pH below 7 are acidic; modern seawater has a pH of about 8.
Meng Guo, a former Yale graduate student in Korenaga’s lab who is now a presidential postdoctoral fellow at Nanyang Technological University in Singapore and the first author of the new study, said, “To understand the origin of life, it becomes important to understand when and how Earth began hosting an ocean with a more neutral pH. But modeling the long-term evolution of ocean pH is a notoriously difficult problem, as it involves almost all of the components of the Earth system: the atmosphere, the ocean, the crust, and the mantle.”
The acidification of the Pacific Ocean in northern Japan is increasing
Ocean pH is largely influenced by atmospheric carbon dioxide (CO2), which is affected by various factors. CO2 levels decrease due to chemical reactions with continents, deep-sea crust, and subduction into Earth’s interior. However, volcanic activity increases CO2 levels.
Based on previous studies, researchers created a model by calibrating and setting parameters for these components. An improved understanding of early Earth tectonics enabled this model.
Their model estimates that it took Earth 500 million years to neutralize ocean acidity enough to support life. While pockets of neutral pH water may have existed earlier, they were not widespread enough for life to thrive.
The researchers said their findings can shed light on early Earth processes and the role those processes play in modern-day climate.
Journal Reference
- Guo, M., Korenaga, J. Rapid rise of early ocean pH under elevated weathering rates. Nat. Geosci. (2025). DOI: 10.1038/s41561-025-01649-9
