Most of Earth's essential elements for life, including most of the carbon and nitrogen in you, probably came from another planet.
Earth most likely received the bulk of its carbon, nitrogen and other life-essential volatile elements from the planetary collision that created the moon more than 4.4 billion years ago, according to a study by Rice University petrologists in the journal Science Advances.
The evidence was compiled from a combination of high-temperature, high-pressure experiments in the researcher's lab, which specializes in studying geochemical reactions that take place deep within a planet under intense heat and pressure. In a series of experiments, researchers gathered evidence to test a long-standing theory that Earth's volatiles arrived from a collision with an embryonic planet that had a sulfur-rich core.
The sulfur content of the donor planet's core matters because of the puzzling array of experimental evidence about the carbon, nitrogen and sulfur that exist in all parts of the Earth other than the core.
One long-standing idea about how Earth received its volatiles was the "late veneer" theory that volatile-rich meteorites, leftover chunks of primordial matter from the outer solar system, arrived after Earth's core formed. And while the isotopic signatures of Earth's volatiles match these primordial objects, known as carbonaceous chondrites, the elemental ratio of carbon to nitrogen is off. Earth's non-core material, which geologists call the bulk silicate Earth, has about 40 parts carbon to each part nitrogen, approximately twice the 20-1 ratio seen in carbonaceous chondrites.
These experiments, which simulated the high pressures and temperatures during core formation, tested the idea that a sulfur-rich planetary core might exclude carbon or nitrogen, or both, leaving much larger fractions of those elements in the bulk silicate as compared to Earth. In a series of tests at a range of temperatures and pressure, researchers examined how much carbon and nitrogen made it into the core in three scenarios: no sulfur, 10 percent sulfur and 25 percent sulfur.
Carbon, by contrast, was considerably less soluble in alloys with intermediate sulfur concentrations, and sulfur-rich alloys took up about 10 times less carbon by weight than sulfur-free alloys.
Using this information, along with the known ratios and concentrations of elements both on Earth and in non-terrestrial bodies, the researchers designed a computer simulation to find the most likely scenario that produced Earth's volatiles. Finding the answer involved varying the starting conditions, running approximately 1 billion scenarios and comparing them against the known conditions in the solar system today.
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