When Grewal modeled how carbon and nitrogen would move in a planet-sized object he found the core's sulfur content is crucial. Carbon is absorbed into low-sulfur cores, but excluded as the sulfur content rises. Meanwhile, Grewal said in a statement. "Nitrogen was largely unaffected,"
Using this information to model a wide variety of scenarios in which carbon, nitrogen, and sulfur could be delivered to Earth, Grewal said: “All the evidence – isotopic signatures, the carbon-nitrogen ratio and the overall amounts of carbon, nitrogen, and sulfur in the bulk silicate Earth – are consistent with a moon-forming impact involving a volatile-bearing, Mars-sized planet with a sulfur-rich core."
Since most planetary scientists are already convinced such an event occurred, causing the Moon's formation, the scenario is easy to believe. The cores of the colliding bodies merged, taking the incoming sulfur and nitrogen out of reach of the crust and mantle, but leaving the carbon behind. Grewal argues a steady rain of smaller meteorites could not produce the mix of elements we see.
Grewal and co-authors say the more spread out the sources of a planet's building blocks within the proto-planetary disk, the more likely it is there will be enough volatile elements to make life possible.
The big question with such research is what implications it has for the chances of life elsewhere. The answer to this depends on the likelihood of a collision as large as the one Grewal describes. It doesn't need to have come at the perfect angle to create a giant moon, but it has to have occurred during a narrow window of time in the planet's formation, possibly making it quite unlikely.