A laboratory experiment shows that the combination of iron, carbon, and water could form a diamond if put under extreme temperatures and pressures. These three elements are all potential ingredients found at the boundary between the Earth's core and mantle.
If this process indeed happens deep inside Earth, it could explain the weird things in the mantle, including the higher amounts of carbon in it than previously thought. Also, it could explain the strange regions known as "ultra-low velocity zones" associated with the mantle, including the two giant blobs found under Africa and the Pacific Ocean.
Simulation of What Happens in the Core-Mantle Boundary
Some scientists think that the weird structures in the mantle and the two giant blobs could date back 4.5 billion years that likely formed when Earth was also formed. But study lead author Sang-Heon Shim, a geoscientist at Arizona State University, told Live Science that they might not be entirely old structures.
In the core-mantle boundary, liquid iron rubs against solid rock, and strange chemistry can happen. Previous studies on earthquake waves showed that materials from the crust could penetrate to the core-mantle boundary at about 1,900 miles (3,000 kilometers) below the surface. Tectonic plates push under one another at the subduction zones and drive oceanic crust into the subsurface.
Rocks from these oceanic crusts contain water that is possible to water also exists in the core-mantle boundary and can drive chemical reactions in that zone. One existing theory that attempts to explain the giant blobs under Africa and the Pacific Ocean is that these blobs are made of distorted oceanic crust pushed deep into the mantle.
Researchers tested their idea and pulled together the ingredients within the core-mantle boundary, namely iron, water, and carbon, then pressed them together that generated pressures of up to 140 gigapascals or 1.4 million times the pressure at sea level.
Shim said that they detected diamonds after monitoring the chemical reaction happening when the samples were heated at 6,830 degrees Fahrenheit (3,776 degrees Celsius). Aside from that, they also detected an unexpected element exchange between the rock and liquid metal.
Diamond Factory: Carbon Transfer Mechanism Sheds Light on Carbon Cycle Inside Earth
Dr. Byeongkwan Ko, a postdoctoral researcher at Michigan State University, pointed out that carbon is important for life and in many geological processes, Sci-News reported. The discovery of a carbon transfer mechanism in the core-mantle boundary will shed light on the carbon cycle deep inside Earth.
Moreso, the discovery shows that the diamond factory in this zone could have been going on for billions of years since the start of the subduction on the planet. In the experiment, iron-carbon alloy and water showed that water and metal react and created iron oxides and iron hydroxides, just like how rusting works.
But instead of rust, it formed into diamonds in the core-mantle boundary. Carbon was initially thought to exist in the core, while the mantle was supposed to have only low carbon. But geoscientists found that there is more carbon in the mantle than previously expected.
Shim explained that hydrogen allowing with iron metal liquid at the pressure present in the core-mantle boundary has reduced the solubility of other light elements in the core. This leads to the solubility of carbon decreasing locally where hydrogen enters from the mantle to the core through dehydration.
Since the stable form of carbon at extreme temperature and pressure is a diamond, the carbon escaping from the liquid outer core into the mantle would become a diamond. The study explains why there is enough supply of carbon in the mantle.
Researchers presented the findings of their study, titled "Water-Induced Diamond Formation at Earth's Core-Mantle Boundary," in the Geophysical Research Letters.
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