Surreal illustration of planetary core with carbon flowing into mantle, sulfur symbolism.

Cosmic Cleanse: How Sulfur in Earth and Mars' Cores Rewrites the Carbon Story

Avery Sinclair in Science & Nature August 2025 • 4 min read.

"New research reveals the surprising role of sulfur in shaping the carbon composition of planetary mantles, offering fresh perspectives on the origins of life."

For decades, scientists have puzzled over the contrasting carbon compositions of Earth and Mars. Earth, with its teeming biosphere, boasts a mantle rich in carbon, while Mars, seemingly barren, holds a fraction of that amount. What drove this divergence? Recent research published in "Geochimica et Cosmochimica Acta" suggests a surprising culprit: sulfur lurking within the planets' cores.

The study challenges long-held assumptions about core-mantle interactions, revealing that sulfur dramatically alters carbon's behavior during planetary formation. This discovery reframes our understanding of how carbon, a fundamental building block of life, was distributed in the early solar system.

By simulating the extreme pressures and temperatures of planetary interiors, researchers have pinpointed the mechanisms by which sulfur influences carbon solubility and partitioning. These findings not only explain the carbon disparity between Earth and Mars, but also provide new insights into the conditions necessary for life to arise on other planets.

The Sulfur Surprise: A Deep Dive into Core Dynamics

Surreal illustration of planetary core with carbon flowing into mantle, sulfur symbolism.

The prevailing theory suggested that Earth's higher carbon content stemmed from a larger initial endowment or more efficient delivery mechanisms. However, this new research highlights the significance of core composition. Specifically, the presence of sulfur in a planet's core has a profound effect on how much carbon the mantle can retain.

Experiments conducted at pressures of 6-13 GPa and temperatures of 1800–2000 °C mimicked the conditions deep within planetary interiors. These simulations revealed that increasing sulfur content in iron-nickel alloy liquids (representing planetary cores) drastically reduces the solubility of carbon. In essence, sulfur 'squeezes out' carbon from the core, forcing it into the mantle.

This groundbreaking study highlights several key findings:

Sulfur decreases carbon solubility in planetary cores.
The effect of nickel on carbon solubility diminishes in sulfur-rich conditions.
The carbon content in alloy liquids decreases with increasing sulfur content.
Alloy liquids are crucial in understanding core-mantle fractionation of carbon.

The team's models indicate that Mars, with its sulfur-rich core, would have expelled a significant portion of its carbon into the mantle during its formative years. Earth, on the other hand, with a relatively sulfur-poor core, retained more carbon within its metallic heart. This fundamental difference in core chemistry set the stage for divergent evolutionary paths.

Implications for Life Beyond Earth

These findings have far-reaching implications for our understanding of planetary habitability. Carbon, the backbone of organic molecules, is essential for life as we know it. By elucidating the mechanisms that control carbon distribution, scientists can better assess the potential for life on other worlds. Planets with sulfur-rich cores might, against initial expectations, possess carbon-rich mantles conducive to the formation of life. This opens up a new avenue for exploration in the search for extraterrestrial life.

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This article is based on research published under:

DOI-LINK: 10.1016/j.gca.2018.07.010, Alternate LINK

Title: Core-Mantle Fractionation Of Carbon In Earth And Mars: The Effects Of Sulfur

Subject: Geochemistry and Petrology

Journal: Geochimica et Cosmochimica Acta

Publisher: Elsevier BV

Authors: Kyusei Tsuno, Damanveer S. Grewal, Rajdeep Dasgupta

Published: 2018-10-01

Everything You Need To Know

How does sulfur in a planet's core affect the distribution of carbon between the core and the mantle?

The research indicates that the presence of sulfur in a planet's core significantly reduces the solubility of carbon within that core. As the sulfur content increases in the iron-nickel alloy liquids representing planetary cores, carbon is effectively 'squeezed out' and transferred to the planet's mantle. This contrasts with planets having less sulfur in their cores, which retain more carbon internally. This is different from older models that assumed the amount of carbon was based on delivery mechanisms and initial endowment.

In what ways does this new research change our previous understanding of carbon distribution during planetary formation?

This discovery challenges previous assumptions by highlighting the crucial role of core composition, specifically the presence of sulfur, in determining how much carbon a planet's mantle can retain. The models and experiments demonstrate that the amount of sulfur in the core directly impacts carbon solubility, reframing how we understand carbon distribution during planetary formation and evolution. Nickel has a smaller effect than previously thought, which changes the carbon solubility.

How did the sulfur content in the cores of Earth and Mars contribute to their differing carbon compositions?

The differing sulfur content in the cores of Earth and Mars significantly influenced the distribution of carbon on each planet. Mars, with its sulfur-rich core, likely expelled much of its carbon into the mantle during its early formation. Earth, conversely, with a core containing less sulfur, retained a larger amount of carbon within its metallic core. This difference in core chemistry contributed to the divergent carbon compositions observed today. Further research is needed to consider the effect of oxygen on the carbon story.

What are the implications of these findings for the search for life on other planets?

The discovery that sulfur in planetary cores influences carbon distribution has significant implications for assessing the habitability of other planets. Planets with sulfur-rich cores could potentially have carbon-rich mantles. This is a condition which might support the formation of life, even if initial expectations based solely on core composition might suggest otherwise. This expands the range of potential candidates in the search for extraterrestrial life and suggests that our understanding of habitability needs to consider core-mantle interactions more closely.

How did scientists simulate the conditions inside planets to study the effects of sulfur on carbon solubility?

The research team simulated the extreme conditions of planetary interiors by conducting experiments at pressures of 6-13 GPa and temperatures of 1800–2000 °C. They used iron-nickel alloy liquids to represent planetary cores and varied the sulfur content to observe its effect on carbon solubility. They were then able to draw conclusions of how much carbon was in the mantle and core.