Oceans are very deep – at least what has been measured – at 7 miles and it is known through studies that water is known to exist well below the oceans; however, there have been no studies to ascertain the depths at which water could be found inside Earth.
Researchers have shown through a new study that water may be more common at extreme depths than believed or thought. According to the study published in journal Science water could be present at up to 400 miles inside Earth and possibly beyond – within Earth’s lower mantle.
Scientist have arrived at this conclusion base don their analysis of microscopic pockets of a trapped form of crystallized water molecules in a sampling of diamonds from around the world. The team behind the study sampled diamonds from locations in Africa and China. They studied the diamonds using a variety of techniques, including a method using infrared light at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab).
The tiny traces of crystallized water, trapped in spaces called inclusions that measure just a few microns (millionths of a meter) in length, contain the molecular signature of ice VII. This crytallized water likely formed from liquid water existing at very high pressures, according to the study.
The structure and chemical studies helped the scientists to determine the pressures and temperatures at which the diamonds formed. This allowed the scientists to estimate the depths of their formation.
Researchers say that it is surprising that so many of the studied diamonds from a random sampling seemed to originate from deep inside the Earth, within and even beyond the so-called transition zone sandwiched between Earth’s upper and lower mantles.
While only about 60 diamonds had previously been confirmed to originate at depths greater than about 190 miles, the latest study added several more to this tally.
Researchers concluded that some of the inclusions likely were formed from fluid existing at depths of 250 miles to 340 miles beneath Earth’s surface. Others may have formed at depths ranging from 380 miles to 500 miles – possibly within Earth’s “shallow” lower mantle.
The pressures that formed these deeper diamonds are estimated at approximately 24 to 25 gigapascals, which is about 224 times more pressure than exists at the bottom the ocean’s deepest point in its Mariana Trench.
The composition of the fluid that was trapped in the inclusions appears to be complex, with traces of carbonates, oxides, and salt, one of the researchers said.
The research team enlisted infrared spectroscopy at the ALS’s Beamline 1.4, which helped them to observe the chemistry of the tiny inclusions.