Most vital elements of the Earth – including most of the carbon and nitrogen in them – were probably from another planet.
The Earth most likely received most of its carbon, nitrogen, and other vital volatiles from the planetary collision that created the Moon more than 4.4 billion years ago, according to a recent study by Rice University's Petrologists in the journal Science Advances .
"Scientists have been working for a long time on studying primitive meteorites It is well known that the Earth and other rocky planets in the inner solar system are volatilely exhausted," said co-author of the study, Rajdeep Dasgupta. "But the timing and mechanism of volatile delivery has been hotly debated, and our first scenario can explain the timing and delivery in a manner consistent with all geochemical evidence."
The evidence was compiled from a combination of high-temperature high-pressure experiments in Dasgupta's laboratory, which specializes in the study of geochemical reactions that take place deep in a planet under intense heat and pressure.
In a series of experiments, study author and undergraduate student Damanveer Grewal gathered evidence for a long-standing theory that the volatile components of the Earth stem from a collision with an embryonic planet that has a sulfur-rich core.
The sulfur content in the nucleus of the donor planet is significant because of the puzzling experimental evidence for carbon nitrogen and sulfur that exist in all parts of the earth except the nucleus.
"The nucleus does not interact with the rest of the earth, but everything about it, the ant matter, the crust, the hydrosphere, and the atmosphere are all interconnected," Grewal said. "Material cycles between them."
A long-standing idea of how the earth received its volatile components was the theory of "late delusion", according to which volatile meteorites, leftover fragments of primal matter from the outer solar system, arrived after the Earth's core was formed. And while the isotopic signatures of the volatile elements of the earth coincide with these original objects, the so-called carbon chondrites, the elemental ratio of carbon to nitrogen is deactivated. Earth's non-core material, which geologists call the bulk silicate earth, has about 40 parts carbon per part nitrogen, about double the ratio of 20: 1
Grewal's experiments simulated high pressures and temperatures. Core formation tested the idea that a sulfur-rich planetary nucleus could exclude carbon or nitrogen, or both, leaving much larger proportions of these elements in the bulk silicate compared to Earth. In a series of tests at various temperatures and pressures, Grewal investigated in three scenarios how much carbon and nitrogen got into the core: no sulfur, 10 percent sulfur, and 25 percent sulfur.
"Nitrogen remained largely untouched". he said. "It remained soluble in the alloys relative to silicates and was excreted from the nucleus only at the highest sulfur concentration."
In contrast, carbon was much less soluble in alloys with intermediate sulfur concentrations, and sulfur-rich alloys required about ten times less carbon than sulfur-free alloys.
Using this information, along with the known ratios and concentrations of elements on both the Earth and non-terrestrial bodies, research scientist Chenguang of Dasgupta, Grewal, and Rice Sun developed a computer simulation to determine the most likely scenario in which the volatiles of the earth have arisen. In order to find the answer, the starting conditions were varied, about 1 billion scenarios were carried out and compared with the conditions known today in the solar system.
"What we found is that all the evidence – isotopic signatures, the carbon-to-nitrogen ratio and the total amounts of carbon, nitrogen and sulfur in the bulk silicate soil – are consistent with a moon-forming effect, with a volatile Planet with Mars size and sulphurous core is involved, "said Grewal.
Dasgupta, the lead investigator of a NASA-funded initiative called CLEVER Planets, which explores how vital elements on remote rocky planets might converge, said that a better understanding of the origin of vital elements of the Earth has implications for our solar system.
"This study suggests that a rocky, earth-like planet has more chances of gaining vital elements as it forms and grows out of gigantic impacts with planets that have sampled different building blocks, perhaps from different parts a protoplanetary disk, "said Dasgupta.
"This removes some constraints," he said. "It shows that vital volatiles can reach the surface layers of a planet, even if they were made on planetary bodies that underwent nucleation under very different conditions."
Dasgupta said it does not seem that Earth's phyllosilicate alone would have reached the vital, volatile budgets that spawned our biosphere, atmosphere, and hydrosphere.
"That is, we can expand our search for ways that cause volatile elements on a planet to come together to support life as we know it."