Imagine you are Carmen Sandiego and you need to reconstruct the itinerary of a globe-trotting using only the beach sand left on the bottom of your suitcase. Even a CSI writer would consider this task implausible, but it sounds similar to the reconstruction of the formation of the Earth. You will get this metaphor if you continue reading.
Building a planet
Scientists analyzed elements and isotopes in meteorites and on the Earth, and they identified where most of the early building blocks for a growing Earth come from, a class of asteroids. However, this class is quite light in volatile elements. Considering that, where do the nitrogen, carbon, and sulfur come from?
There are a lot of potential explanations which are only making the job harder, but some of them suggest that much more of these elements are carried by another class of asteroids, their ratio being off. The Earth would have been left short on carbon if this class of asteroids had arrived after the core of the Earth had formed.
A group at Rice University led by Rajdeep Rasgupta and Damanveer Grewal tested another explanation by melting stuff in the lab. They mixed iron-nickel alloys with varying amounts of nitrogen, carbon, and sulfur along with basalt rock in a special setup. After that, the mix melted after being put under extreme pressure. To see how the elements moved around, they analyzed the blobs of metal that encased in the glass formed from the basalt that melted after the mix cooled off.
During their experiment, they realized that the amount of nitrogen stuck in the metallic blobs was a little smaller when lots of sulfur was present. Something even more important is that after more sulfur was added the amount of carbon in the metallic blobs dropped off sharply.