Earth’s internal structure continues to reveal details that reshape established scientific explanations about the planet’s formation. One such development concerns the origin and distribution of water. For decades, the dominant explanation suggested that water was delivered to Earth by icy comets during its early history. Geological and seismic research, however, presents a more intricate picture. Current evidence suggests that a considerable amount of water may be located deep within the Earth’s mantle, far below the Earth’s crust. Situated about 700 kilometres below the Earth’s crust, this body of water is not in a liquid state but is instead locked in within minerals, according to Brookhaven National Laboratory. Its potential volume is considerable, even surpassing that of all the oceans on the Earth’s crust, thus reinvigorating research on the Earth’s water cycle.
Why Earth’s ‘hidden ocean’ isn’t liquid: Water trapped in ringwoodite explained
The term ocean is often used informally to describe this reservoir, although it differs entirely from surface bodies of water. According to the BNL reports, the water exists within a high-pressure mineral known as ringwoodite, which forms under extreme conditions in the mantle. In this state, water is chemically bound within the mineral’s crystal structure rather than existing as a free-flowing liquid.Laboratory experiments simulating mantle conditions have confirmed that ringwoodite can incorporate significant amounts of water. When extrapolated across, the total volume becomes considerable. This form of storage represents a stable and long-term component of Earth’s internal system.
Revisiting the origin of Earth’s water
The presence of water in the deep mantle supports the theory that Earth has kept its water since it was formed. The theory implies that instead of getting water from external sources such as comets, it has been part of the planet since it was formed. The internal water could have moved towards the surface over time through volcanic activities. The theory is consistent with observations that the volume of water in the oceans has remained constant over time.
Seismic evidence revealing water in Earth’s mantle
Direct exploration of depths approaching 700 kilometres remains beyond current technological capabilities. As a result, scientists rely on indirect methods, particularly seismic analysis. Earthquake-generated waves travel through the planet and change speed depending on the materials they encounter. In certain areas, seismic waves have been observed to slow down, a characteristic often associated with the presence of water within minerals. These observations, gathered through extensive seismometer networks, provided initial evidence for water in the mantle.According to Schmandt and Jacobsen’s findings, which build on a discovery reported in the journal Nature, further support comes from laboratory experiments and the analysis of ringwoodite samples found within diamonds brought to the surface by volcanic eruptions. These samples contained measurable amounts of water, confirming theoretical predictions.