While some researchers successfully study deep space, others are trying to understand what lies hidden beneath the impenetrable surface of our planet. In a new study, geophysicists used the computational power of a supercomputer and discovered something they did not expect to see at all.

The Earth's solid surface—the lithosphere—is divided into giant plates that are in constant motion. This causes continental drift—with a periodicity of 400–600 million years, landmasses gather together and then diverge again. Currently, the Earth is in the middle of a cycle: the Atlantic Ocean is expanding by several centimeters per year, while the Pacific, on the contrary, is shrinking and will eventually disappear completely. Asia will merge with America, joined by Australia and Antarctica.

The thickness of the plates is not uniform. Continental crust has an average thickness of about 40 kilometers, while oceanic crust is only six or seven. At the junction, a thinner plate "dives" under a massive one and melts in the mantle. The place where this happens is called a subduction zone. The most famous example of such a line is the Pacific Ring of Fire, a belt of volcanic activity that passes through Hawaii, Kamchatka, and California, among other places.

In a new study, geologists from the Swiss Federal Institute of Technology in Zurich, together with colleagues from the California Institute of Technology, decided to look under the lithospheric plates to study the composition of the Earth's mantle.

It is impossible to do this directly: it is impossible to drill through the crust to take samples or measure the temperature and pressure of the molten substance. Therefore, scientists can only guess what exactly they saw. According to one version, these are not remnants of subducted plates, but ancient material rich in silicon, preserved in the mantle since its formation—that is, about four billion years ago. According to another, these are clots of iron-rich rock that accumulate in one place as a result of the movement of the molten substance. Experts admit that additional data and, most likely, new research methods are needed to answer the question.

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