earth mantle
Credit: Pixabay/CC0 Public Domain

There is a question about the structure of the Earth. The core, upper and lower mantle, and the crust make up the structure. Most of our planet's volume is made up of the mantle. The lower mantle is more dense and hotter than the upper mantle.

The lower mantle has an important role to play in the Earth's evolution, including how Earth has cooled over billions of years, how materials have been circulating, and how water is stored and transported from/ to the deep interior over a geologic time scale.

The lower mantle's mineralogy has been studied for more than 70 years. The three main minerals in the lower mantle are bridgmanite, ferropericlase, and davemaoite.

A team of scientists, including a former PhD student and a professor, have just published a study in Nature.

Two minerals, bridgmanite and davemaoite, have different types of crystal structures. Some materials with the perovskite-type structure have shown superconductivity.

Under a high- temperature environment, minerals with similar crystal structures can become single minerals. Mineral diopside has both calcium and magnesium in it's structure. Studies show that davemaoite, rich in calcium, and gmanbridite, rich in magnesium, remain separate throughout the lower mantle.

Despite the fact that they have very similar atomic-scale structures, davemaoite and bridgmanite don't merger. Researchers have been fascinated by this question for two decades. The answer from experiments has been that the two minerals are separate. We needed some new ideas in experiments.

The research group was able to try different heating techniques in the experiment. They increased the temperature very quickly to the high temperature related to the lower mantle, reaching 3000–3500 F. The reason for this was that once two perovskite-structured minerals form it becomes very difficult for them to combine even if one of them is stable.

Ko and Shim were able to avoid the formation of two minerals by heating the samples quickly. Once they get to the temperature of the lower mantle, they use X-ray beams to look for minerals. They found that only one type of mineral form. davemaoite and bridgmanite became a single mineral at high temperatures.