A new form of water ice was recently discovered, trapped inside diamonds found deep beneath the Earth’s crust. This new finding, researchers noted, marks the first time the substance known as ice-VII was found to naturally occur on our planet.
According to a report from the Los Angeles Times, ice-VII differs from regular ice, or ice-I, as oxygen atoms are arranged in a cubic shape, instead of hexagonal shape. This newly discovered water ice form is also approximately one-and-a-half times denser than conventional ice while differing from other phases of ice due to its ability to withstand increasing pressure and remain “fairly stable” under such conditions. These are conditions that can only exist in Earth’s mantle, several hundreds of feet below the surface, in an extremely hot area known as the transition zone, as noted by Science Alert.
Before the release of the new findings, which were published Thursday in the journal Science, researchers had yet to discover ice-VII occurring naturally on our planet. They had, however, speculated that it might be common in other icy parts of the solar system, including Saturn’s moons Enceladus and Titan and Jupiter’s moon Europa. And while earlier research had suggested that this form of water ice could be created artificially in a laboratory, the new study points to diamonds having the right chemical features and properties to allow small amounts of ice-VII to be produced naturally on Earth.
With the new study published around the same time as another paper that documented the presence of calcium silicate perovskite (CaSiO3) in diamonds found deep below our planet’s surface, Science Alert noted that the researchers behind the ice-VII study were able to spot the water ice in a similar way – in the form of sub-transition zone water molecules trapped and pressurized within the diamonds’ flaws. These water molecules were most likely trapped in liquid form about 400 to 500 miles below Earth’s surface as diamond crystals began to form. However, it was only when the molecules ascended and adjusted to cooler temperatures when they got fully encapsulated and transformed into ice-VII form, the researchers wrote.
As explained by the Los Angeles Times, the “teeny bits” of the chemicals around minerals that get encapsulated within them during their formation are known as inclusions. When diamonds are being created, these inclusions get transported up to the surface together with some of them and do not change in volume or in pressure from the time they get encapsulated.
“Usually the extremely deep minerals that come up to the surface are not stable once they experience low pressures,” said California Institute of Technology mineralogist and study author George Rossman.
“They crack and whatever inclusions they had in them are lost. But if a diamond comes up fast enough, it doesn’t change.”
Although Science Alert wrote that the inclusions offer the first proof that our planet may be hiding a substantial amount of water deep beneath its surface, the publication stressed that the study did not specify just how much water might exist, or how common the substance may be in those depths.
Despite the few unanswered questions that popped up, the researchers were nonetheless excited by their discovery of water ice inclusions, especially since the International Mineralogical Association recognized ice-VII as a mineral, according to the Los Angeles Times. According to study lead author Oliver Tschauner, a geoscience professor at the University of Nevada-Las Vegas, the findings were entirely accidental, as his team had originally sought to find an “unusual phase of carbon dioxide” within diamonds.
“Water in diamonds is not unknown, but finding this very high pressure form of water ice intact, that was really fortuitous,” said Tschauner.