Rice researchers may have solved the mystery of how the carbon in our bodies arrived on Earth: through a collision with an embryonic planet 4.4 billion years ago.

A current popular theory involves relatively volatile elements, including compounds of carbon, sulfur, nitrogen and hydrogen, arriving through meteorites and comets over 100 million years after the formation of the solar system, but there is no known meteorite that could account for the ratio of these elements on Earth’s surface.

In searching for another theory, Rice petrologist Rajdeep Dasgupta and his team considered the composition of the Earth’s core, which is thought to be just iron, nickel, and carbon due to iron’s strong affinity for carbon. The researchers also utilized Dasgupta’s lab, which has the ability to reproduce the high pressures and high temperatures existing 250 miles below the Earth’s surface.

Experimentation revealed that if the iron alloys in the core were silicon or sulfur rich, iron’s strong affinity would be altered and carbon would be found not in the core but in the silicate mantle. The researchers mapped out concentrations of carbon under differing levels of sulfur and silicon and compared them with concentrations found in the earth’s mantle to hypothesize that an embryonic planet with a silicon-rich core collided with Earth. According to Dasgupta, that planet was absorbed; its core combined with Earth’s and its carbon-rich mantle mixed with Earth’s.

Dasgupta said further research is necessary to account for the presence of other volatile elements, but this scenario is promising in providing an explanation for the presence of carbon and sulfur on Earth.