Discovery rewrites Earth's history

A team of scientists in China has identified a key mechanism that explains how Earth could have stored huge amounts of water in the early stages of its existence. The discovery offers new insight into Earth's spectacular transformation from a planet covered in magma oceans to the blue, habitable world it is today, Xinhua news agency reported.

The study, conducted by researchers at the Guangzhou Institute of Geochemistry, part of the Chinese Academy of Sciences, was published in the prestigious journal Science and provides experimental evidence for the role of Earth's deep mantle as a major reservoir of water more than four billion years ago.

One of the great questions of planetary geology has been what happened to the water after the magma oceans that covered the primitive Earth cooled and crystallized. "What happened to the water after the crystallization of the early Earth's magma oceans? For the deepest mantle, the answer has long remained elusive,” says an editorial in Science accompanying the study. The new research suggests that the answer lies in bridgmanite, the most abundant mineral in Earth's lower mantle.

• Bridgmanite - an unexpected reservoir of water

Until now, bridgmanite was thought to be a mineral with a limited capacity to store water. However, experiments by the Chinese team contradict this hypothesis. The researchers have shown that bridgmanite can store significant amounts of water, and this capacity is temperature-dependent. Surprisingly, the hotter the conditions, the more efficient the mineral becomes at capturing water molecules. To reach these conclusions, scientists recreated the extreme conditions in the Earth's lower mantle, where pressures are enormous and temperatures can reach around 4,100 degrees Celsius. The experiments were carried out using a diamond-anvil cell, combined with laser heating, a cutting-edge technique that allows the simulation of extreme environments inside planets. The results revealed a geological paradox: in an extremely hot environment, bridgmanite is able to more efficiently capture the water released as magma cooled and solidified.

According to the study's estimates, this mechanism would have allowed the isolation, in the Earth's solid mantle, of an amount of water equivalent to between 8% and 100% of the total volume of modern oceans. However, this huge reserve did not remain permanently locked inside the planet. Over billions of years, the water was gradually brought back to the surface through volcanic activity, contributing decisively to the formation of the oceans and the emergence of the conditions necessary for life.

• Implications for the Origin of Life and Other Planets

The discovery not only rewrites part of Earth's early history, but also has important implications for understanding the evolution of other rocky planets. If planetary mantles can act as massive reservoirs of water, this could explain why some apparently dry planets may have had, in the past or even now, internal resources capable of supporting processes favorable to life.