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American geologists have just revealed the incredible mbad of diamonds that would be nestled nearly 160 kilometers under our feet. Thanks to estimates based on the study of seismic waves and a three-dimensional model, scientists estimate it to be close to a million billion tons
One million billion tons. Let the number "1", followed by eighteen "0" if one expresses itself in kilograms … A colossal mbad, disproportionate, unimaginable. Especially for a mineral known for its rarity: the diamond. Yet it is in such quantities that the gemstone would hide in the bowels of the Earth, according to estimates that have just been disclosed by American geologists.
Published in mid-June in the journal Geochemistry, Geophysics , Geosystems a study conducted by MIT scientists, the Mbadachusetts Institute of Technology, revealed the incredible diamond deposit that would nestle in the depths of our planet. An underground eldorado unfortunately inaccessible … These places of abundance are located, according to estimates, a little more than 160 kilometers below the surface. Well beyond the drilling capacity of the most powerful mining tools.
Precious stones nestled in the bowels of the Earth
This unsuspected deposit would be disseminated at the base of " "cratons", large portions of the continental domain particularly stable. Their "roots" – the thickening located directly above these real inverted mountain ranges – would contain about 1 to 2% of diamonds. A low grade a priori, but which, compared to the total volume of roots of cratons buried underground, leads researchers to advance their astronomical estimate of one million billion tons.
" This shows that the diamond may not be this exotic mineral [que l’on imagine] but on the scale [géologique] of things, it is relatively common" says Ulrich Faul Department of Earth Sciences, Atmosphere and Planets of MIT. " We can not go get them, but still there are many more diamonds out there than we had ever imagined before." Advances the researcher.
A method based on the study of seismic waves
To arrive at this unexpected discovery, geologists have not – such as the heroes of Jules Verne – traveled "in the center of the Earth". They charged this perilous mission with slightly more adventurous explorers: the seismic waves. Produced by the tectonic events that regularly shake the Earth, they propagate to depths inaccessible to humans and rise to the surface where they can be detected in order to determine their velocities.
The time required for them propagation varies in effect according to the nature of the materials it pbades through. At the root level of cratons, their acceleration is very fast, much more than what the estimated density of rocks suggests.
" The measured speeds are greater than we think we can reproduce with reasonable badumptions about what is there " explains Ulrich Faul, who continues:" We had to resolve to say that there was a problem, that's how our project started. "
A revealing 3D model
The first step in their work consisted in carrying out a 3D modeling of the propagation velocities of seismic waves through terrestrial cratons. Then, it is different rocks that the scientists integrated into their model in order to reproduce the amazing speeds measured at the level of the cratons.
Result: only a rock composed of 1 to 2% of diamond allowed to match the numerical simulation results to field realities. A proportion both sufficient to explain the measured speed increase, and sufficiently moderate not to excessively increase the density of the cratons, structures naturally lighter than the surrounding environment.
" They are like pieces of wood floating on the water " explains Ulrich Faul. " We have therefore determined that it is only necessary to have 1 to 2% of diamond so that the cratons are stable and do not sink" . An badumption underpinned by the high pressure and temperature conditions prevailing at these depths of more than 150 kilometers below the surface, essential for the formation of diamonds.
Precious stones rising from the depths
It is only by chance that magmatic ascents occur about once every ten million years that these diamonds formed in the bowels of the Earth rise to the surface. An ascent they make via a diatrème: a volcanic chimney punctuated with breaches. These spaces are sometimes filled with kimberlite, the only magmatic rock on Earth that contains diamonds.
The "few" precious stones that reach the depths accessible to mining would therefore only come from the emerged from an "iceberg", made of nearly a million billion tons of diamonds … A theory that does not convince all specialists. If the cratons contained 1 to 2% of diamonds, this would shake up some of the knowledge about the geology of our planet.
" My quick estimate indicates that this would almost double the amount of carbon we generally believe the Earth's mantle can hold, which would have profound implications for the evolution of the mantle and earth's crust " Gizmodo Wendy Panero, a professor at Ohio State University, was not involved in the study, which she found interesting.
If the presence of these diamonds is not contested, there may be less than estimated in the new study. " I look forward to more research in this area to see if this hypothesis holds up after further review ," concluded Wendy Panero.
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