Unlocking the Secrets of Ancient Atmospheres: How Sulfur Compounds Shaped Early Earth
Cade Christensen, a Ph.D. student at the University of North Carolina at Chapel Hill, and Dr. Jason Surratt, a professor in the Department of Chemistry, conducted laboratory experiments that simulated atmospheric conditions on early Earth.
February 20, 2025 I By Dave DeFusco
For scientists studying the origins of life and the evolution of planetary climates, understanding atmospheric aerosols is essential. These tiny particles, suspended in the air, influence climate, surface conditions and even the potential habitability of planets. A recent ACS Earth and Space Chemistry study, “Chemical Characterization of Organosulfur Compounds in Aerosols from Archean Analog Photochemistry: Insights from Liquid Chromatography and High-Resolution Tandem Mass Spectrometry,” sheds new light on a key component of ancient atmospheric chemistry: organosulfur compounds.
Aerosols play a critical role in regulating temperature, blocking harmful ultraviolet radiation and affecting cloud formation. They can be composed of both inorganic and organic compounds, originating from gases like methane, carbon dioxide, nitrogen and sulfur gases, such as hydrogen sulfide and sulfur dioxide. When these gases undergo chemical reactions triggered by sunlight, they form aerosols that may have influenced the early Earth’s climate and possibly even the emergence of life.
Recent research has indicated that hydrogen sulfide significantly contributes to organic aerosol production, potentially through the formation of organosulfur compounds. However, until now, scientists lacked a detailed understanding of the molecular makeup of these compounds, leaving questions about their role in planetary evolution unanswered.
To bridge this knowledge gap, Cade Christensen, a Ph.D. student at the University of North Carolina at Chapel Hill, and Dr. Jason Surratt, a professor in the Department of Chemistry, conducted laboratory experiments that simulated atmospheric conditions on early Earth. They exposed a mixture of gases—0.5% carbon dioxide; 0.1% methane; and 5 parts per million of hydrogen sulfide in a nitrogen background—to ultraviolet light to mimic ancient atmospheric reactions. The resulting aerosols were then analyzed using a sophisticated technique called hydrophilic interaction liquid chromatography coupled with high-resolution mass spectrometry. This method allowed them to identify and characterize 60 different organosulfur compounds with remarkable precision.
Their analysis revealed that sulfur existed in multiple oxidation states, forming functional groups such as sulfates, sulfonic acids, sulfites, sulfinic acids and thiols. Five specific compounds—methyl sulfate, ethyl sulfate, methane sulfonic acid, ethane sulfonic acid and isethionic acid—accounted for 6.2% to 7.9% of the total aerosol mass, highlighting their potential significance in the Archean sulfur cycle, which refers to the movement of sulfur through the Earth’s systems during the Archean eon, a very early geological era characterized by a largely oxygen-poor atmosphere.
“Our findings suggest that organosulfur compounds played a more substantial role in early Earth’s atmospheric chemistry than previously thought,” said Christensen. “These compounds could have influenced climate patterns, cloud formation and even the chemical processes leading to life’s origins.”
Beyond Earth, this research has implications for the study of other planetary bodies. Many scientists are investigating the atmosphere of planets and moons, such as Jupiter, Saturn and Titan, as well as exoplanets outside Earth’s solar system. Understanding the role of organosulfur compounds in these environments could provide critical insights into planetary evolution and habitability.
“Our work represents the most detailed molecular characterization of organosulfur compounds in laboratory-simulated haze to date,” said Dr. Surratt. “Our findings pave the way for future studies exploring how these compounds interact with other atmospheric components and contribute to planetary climate systems. By continuing to investigate the intricate chemistry of ancient atmospheres, we’re uncovering new pieces of the puzzle that explain how planets evolve—and, perhaps, how life itself began.”