There are many theories surrounding the origin of water on Earth. It was long believed that comets and asteroids brought water to the Earth's surface early in time. But a recent discovery has overturned all other theories. Geologists have discovered ringwoodite, a type of hydrous mineral, at a depth of 700 kilometers below the Earth's surface. This suggests that water on the Earth's surface may have gradually emerged from the depths of the early Earth.
Ninety million years ago, a volcanic eruption in Brazil brought an imperfect diamond to Earth's surface. Researchers discovered ringwoodite, which contains hydroxyl ions, inside the diamond.
Before the discovery of the flawed diamond, the idea of a vast ocean deep beneath the Earth's surface existed only in a Jules Verne novel. «"Journey to the Center of the Earth". The diamond was found near the São Luís River in Juina, Brazil. It was brought to the Earth's surface by a volcanic eruption in a kimberlite-containing lava flow 90 million years ago. The diamond was discarded because it had no commercial value. But for geologists, it offered a rare glimpse into the Earth's interior.
A hermetically sealed inclusion containing minerals trapped within the diamond during its formation was discovered. Graham Pearson of the University of Alberta in Edmonton, Canada, decided to investigate this inclusion. Using infrared microscopy, he discovered the presence of hydroxyl ions. Hydroxyl ions are typically formed from water. Therefore, these ions indicate the presence of water at the site of diamond formation.
Research has shown that the diamond formed in the Earth's mantle, indicating the presence of water deep below the planet's surface.
Geophysicist Steve Jacobsen of Northwestern University in Evanston, Illinois, and his team attempted to calculate the depth at which the diamond formed. A careful study of the diamond's defects revealed that it was composed of the mineral ferropericlase. Ferropericlase is composed of iron and magnesium oxides. It is capable of absorbing other metals, such as chromium, aluminum, and titanium, at extremely high temperatures and pressures. These conditions are typical of the lower mantle. However, additional minerals were gradually released as the diamond was exposed to milder conditions during its ascent to the Earth's surface. The fact that these metals were once present in the diamond during its formation indicates that it must have formed in the lower mantle.
Jacobsen and his team studied seismic waves from 500 earthquakes and found that wet ringwoodite is indeed present in the mantle's transition zone at a depth of 700 kilometers.
To confirm the presence of hydrous ringwoodite in the mantle, Jacobsen and his team studied seismic waves. Seismic waves are generated by earthquakes, propagating throughout the Earth's interior, including the core. As Jacobsen puts it, "They make the Earth ring like a bell for several days afterward." These waves can be detected at the surface. By measuring the wave speed at different depths, geologists can determine the type of rock the waves are traveling through.
For this study, Jacobsen and his team used 2,000 seismometers. They studied seismic waves generated by more than 500 earthquakes. They already knew that waves slow down when passing through water-containing ringwoodite. During the study, they discovered signs of wet ringwoodite in the transition zone at a depth of 700 kilometers. This is the region separating the upper and lower mantle. The pressure and temperature at this depth can squeeze water out of ringwoodite. Jacobsen said, "It's a rock with water along the grain boundaries, almost as if they're sweating.".
Jacobsen's research findings prove the existence of a deep aquifer within the Earth. This will help us understand how the Earth's waters recycle themselves.
Graham Pearson claims to have discovered another ringwoodite crystal containing water.
Following his research, Jacobsen said: "This is the most compelling evidence yet of a water cycle on the planet. The key takeaway is that the Earth's water cycle is much larger than we ever imagined and extends deep into the mantle.".
According to Lydia Hollis from the University of Glasgow (UK), "Ultimately this research will help us better understand how our planet processes its waste.".
[sources: 1, 2, 3, 4, 5, 6]