For about 30 years, scientists have been aware of areas of continental size in the interior of the Earth, located at a depth of almost 3 thousand kilometers. These sites have been the subject of extensive research, and many ideas have been put forward explaining what they are. Finally, geologists have proven that these features of the bowels can consist of ancient fragments of the earth’s crust that have descended thousands of kilometers, almost to the very core of our planet.
Most of the earth’s crust consists of a rock called basalt. At the junctions of lithospheric plates, high pressure causes it to sink into the bowels of the earth. As these basaltic rocks move inland, they are exposed to higher pressures and temperatures and enter into various reactions. One of the results of these reactions is the production of perovskite calcium silicate (Ca-Pv), which is considered the third most abundant mineral in the Earth’s mantle at depths over 660 kilometers.
Knowledge of the mantle of our planet so far has been limited by the difficulty of studying Ca-Pv.
This is technically difficult because this mineral is not reproducible under ordinary conditions, so to study any of its properties, you must ensure the conditions of the Earth’s bowels where it is stable: pressures of more than 100,000 atmospheres and temperatures above 1000 degrees Celsius.
-Andrew Thomson, lead author Research from University College London (UK)
To take measurements, an international team of researchers conducted experiments on the Large Volume Press instrument of the European ESRF synchrotron, designed to determine the physical characteristics of materials under high pressure and temperature conditions.
The ESRF’s Large Volume Press is Europe’s unique tool on which we can collect real-time diffraction data under pressure and temperature conditions consistent with the interior of the Earth.
-Wilson Crichton, a scientist at the Large Volume Press project
In addition to collecting X-ray images and measuring the crystal structure of Ca-Pv, the team also measured the time required for the passage of ultrasonic waves through the samples at various combinations of pressure and temperature. This allowed them to determine the structure, density, wave propagation velocity, and elastic properties of Ca-Pv in the conditions of the Earth’s interior. Interestingly, the properties of Ca-Pv were different from those expected, but allowed scientists to interpret some of the conflicting ideas of deep Earth.
Our results show that the subducted oceanic crust is mapped by anomalies throughout the lower mantle. In particular, we found that large, continent-sized areas of abnormally low wave velocity, visible at a depth of more than 2,500 kilometers below the Earth’s surface, are explained by areas with moderate inclusion of processed oceanic crust. We also observed crystallographic phase transitions in Ca-Pv, which also explain the mysterious seismic wave discontinuities observed at a depth of 800–1200 kilometers.
Earth's Underground Continents
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