The boundary zone between the molten metal core and the mantle may be a diamond factory.
Under extreme temperatures and pressures, the combination of iron, carbon and water can form diamonds. It could explain why the mantle has more carbon in it than scientists think.
There are strange structures in the core-mantle boundary where waves from earthquakes slow down dramatically. Two giant blobs under Africa and the Pacific Ocean are associated with the ultra low velocity zones and can be just a few miles across. They don't know what they are. Some scientists think they are from 4.5 billion years ago. According to the new research, some of these zones may owe their existence to plate tectonics, which may have started 3 billion years ago.
The lead author of the study told Live Science that they are adding a new idea to the study.
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Liquid iron rubs against the rock. It's like the rock-to-air interface at Earth's surface. Strange chemistry can occur at high pressures and temperatures.
Studies that use the reflections of earthquake waves to image the mantle have shown that materials from the crust may enter the core-mantle boundary. The plates push each other under the ocean. Water is locked in the rocks of the ocean. It is possible that water exists in the core-mantle boundary and can cause chemical reactions down there. One theory about the pair of mantle blobs under Africa and the Pacific is that they are made up of distorted oceanic crust that has been pushed deep into the mantle.
The researchers pressed the ingredients together with anvils made of diamond, generating pressures of up to 140 gigapascals. The pressure at sea level is about one million times greater. The samples were heated to over 6000 degrees Fahrenheit.
When we heated the sample, we monitored what happened. We found an unexpected element exchange between rock and liquid metal.
Water behaves differently under the pressure and temperature of the core-mantle boundary. Most of the core is made of iron because of the high pressure. Oxygen from water stays in the mantle.
The light elements in the core seem to be pushed aside by the hydrogen. The carbon leaves the core and enters the mantle. Diamond is the most stable form of carbon.
"That's the way diamonds form," he said.
Most diamonds that make their way to the surface and form a few hundred kilometers deep are not the same diamonds that are used in an engagement ring. The carbon from the core-mantle diamonds could be distributed throughout the crust.
Based on the amount of elements in stars and other planets, the mantle has more carbon than expected. There are diamonds in this layer of Earth. If 10% to 20% of the water in the ocean makes it to the core-mantle boundary, it could produce enough diamonds to explain the levels of carbon in the crust.
If that is the case, many of the low-velocity zones in the mantle might be areas of water driven melt.
The next challenge is proving this happens thousands of kilometers below the surface. There are at least two ways to look for evidence.
It is possible to find structures within the core-mantle boundary that are clusters of diamonds. Researchers would need to find high-velocity zones next to the already discovered regions where waves travel slowly because diamonds are dense and transmit earthquake waves quickly. The work isn't yet published, but other researchers are looking into it.
It is possible to study diamonds that are deep in the Earth's mantle. Under very high pressure, these diamonds can sometimes make it to the surface with small pockets of minerals that can form only under the right conditions.
The Hope Diamond may have formed very deep in the planet. There is barely any material to measure when scientists claim to have found very deep diamonds. He said it might be worthwhile to look for core-mantle boundary inclusions.
If someone could find proof for that, that would be a discovery.
They reported their findings in the journal.
It was originally published on Live Science
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