According to a study conducted by the petrologists of Rice University (USA), the Earth received most of its carbon, nitrogen and other vital volatile elements as a result of a collision with a planet Theia that created the moon more than 4.4 billion years ago.
For the first time, our scenario will be coordinated with the timing and method of delivering volatile elements to Earth with all geochemical data.
-study co-author Radjip Dasgupta
Evidence aimed at testing the long-standing theory that the volatile matter of the Earth came about as a result of a collision with a protoplanet containing a rich gray core came from a combination of high-temperature experiments under high pressure in a laboratory specializing in studying geochemical reactions occurring deep in the bowels of our planet intense exposure to heat and pressure. The sulfur content in the core of the donor object is significant because of the surprising array of experimental data on carbon, nitrogen and sulfur present in all layers of the Earth except the core.
One of the old ideas about how the Earth received volatile substances was the theory of “late bombardment”, according to which meteorites rich in volatile substances arrived after the formation of the core of our planet. And although the isotope signatures of volatile substances of the Earth correspond to these primordial objects, the elemental ratio of carbon to nitrogen is knocked out of the overall picture. The non-basic material of the Earth, which geologists call the bulk silicate Earth, contains about 40 parts of carbon for each part of nitrogen, which is approximately twice the ratio observed in meteorites.
Simulation of high pressure and temperature during nucleation allowed the idea that the sulfur-rich planetary core could contain almost no carbon or nitrogen, leaving much larger portions of these elements in bulk silicate. In a series of tests at different temperatures and pressures, it was determined how much carbon and nitrogen was incorporated into the core in each of the three scenarios: no sulfur, 10 percent sulfur, and 25 percent sulfur.
It turned out that the nitrogen was practically unaffected. It remained dissolved in the alloys and was excluded from the core only at the highest sulfur concentration. Carbon had a different story: sulfur-rich alloys showed about 10 times less carbon than sulfur-free alloys.
Computer simulation showed the most likely scenario that gave rise to volatile substances of the Earth. Scientists have discovered that all the evidence (isotopic signatures, carbon-to-nitrogen ratios and total carbon, nitrogen and sulfur in the bulk silicate Earth) correspond to the effects of a planet the size of Mars with a rich gray core, as a result of which the Moon originated.
A better understanding of the origin of the vital elements of the Earth is also important outside the solar system. The researchers found that elements can enter the surface layers of the planet, even if they originate on bodies born under completely different conditions.
This study shows that a rocky, Earth-like planet is more likely to acquire vital elements if it is formed and grows as a result of gigantic collisions with planets that unite building blocks from different parts of the protoplanetary disk. It seems that the bulk silicate of the Earth itself would not have been able to achieve the vital composition of the elements defining our biosphere, atmosphere and hydrosphere.
-Rajdip Dasgupta
Vital chemical elements found on Earth are alien origin
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