The Origin of Water

Water is an ancient matter—older than any living organism on Earth. Water formed during the early stages of Earth’s evolution, making it nearly as old as the planet itself, while human origins date back only a few million years. Humanity’s understanding of water has been long and complex, involving rational inquiry, scientific analysis, as well as religious and superstitious interpretations.

There are currently around 32 theories regarding the origin of water on Earth. One theory suggests that a primordial nebula containing water molecules existed before Earth’s formation—similar to meteorites that contain an average of 0.5% water—and that this water descended to Earth after the planet formed. Another theory holds that water-forming elements (hydrogen and oxygen) emerged only after Earth’s formation. Under suitable conditions, hydrogen and oxygen combined to form hydroxyl groups (OH), which then underwent complex changes to produce water (H₂O).

Dutch astronomer Oort proposed that Earth’s water primarily originates from the mantle within the planet’s lithosphere. Roughly half of lithospheric material consists of silicon, including various silicates and water. These rocks dehydrate under certain temperatures and suitable conditions (such as volcanic eruptions), thereby forming Earth’s water. American scholar Kennedy and others suggested that when rocks are fully mixed during melting, they contain 75% silicate and 25% water. During Earth’s early formation, frequent volcanic eruptions accelerated the formation of water.

Some believe that the solid dust composing primordial Earth was actually fragments from exploded aging stars—mostly inorganic salts containing crystalline water within. This crystalline water, released by Earth’s internal heat, turned into water vapor. Upon reaching saturation in the atmosphere, it cooled into clouds, fell as rain, and gradually accumulated in low-lying areas to form lakes, rivers, and eventually oceans.

The prevailing view is that during Earth’s early days, most water existed as crystalline water within the planet’s interior. As high temperatures decomposed internal materials, vast amounts of gas were released through volcanic activity, carrying water vapor into the atmosphere. Around the early Archean era, temperatures began to drop, water vapor condensed into dense clouds, and as Earth cooled further, torrential rains fell, accumulating on the primordial land to form the earliest rivers, lakes, and seas—the primordial hydrosphere.