Rethinking Sulfur’s Early Role in Life

Sulfur—much like carbon—is a core building block of life, appearing in key amino acids that form the foundation of proteins. While sulfur was present in Earth’s early atmosphere, scientists long believed that complex organic sulfur molecules, including amino acids, could only arise after life had already begun.

Figure 1. Early Earth’s Atmosphere May Have Sparked Life.

Previous attempts to recreate early Earth conditions rarely produced significant amounts of sulfur-based biomolecules. When such molecules did appear, they formed only under highly specific and improbable environmental circumstances. Figure 1 shows Early Earth’s Atmosphere May Have Sparked Life

These assumptions shaped scientific reactions when the James Webb Space Telescope detected dimethyl sulfide—a compound produced by marine algae on modern Earth—on the exoplanet K2-18b. For many researchers, the find raised the possibility of biological activity on another world.

New Experiments Shift the Picture

Earlier research by Reed and senior author Ellie Browne, a chemistry professor and CIRES fellow, revealed that dimethyl sulfide can be produced in the lab using only light and simple atmospheric gases—suggesting the molecule might arise naturally even on lifeless worlds.

Building on that discovery, Browne, Reed, and their colleagues set out to test what Earth’s primordial atmosphere itself could generate. They illuminated a mixture of methane, carbon dioxide, hydrogen sulfide, and nitrogen to recreate prebiotic atmospheric conditions.

With the help of an ultra-sensitive mass spectrometer capable of identifying trace chemicals, the team found that their early Earth simulation produced a diverse suite of sulfur-based biomolecules—including the amino acids cysteine and taurine, as well as coenzyme M, a key component in metabolic processes.

A Sky Capable of Supporting a Nascent Biosphere

The team then estimated how much the entire primordial atmosphere could have produced. Their calculations suggested that early Earth’s sky might have generated enough cysteine to supply roughly one octillion (1 followed by 27 zeros) cells. For context, Earth today contains about one nonillion (1 followed by 30 zeros) cells.

“While it’s not as many as exist now, that was still an enormous amount of cysteine in a lifeless environment,” Reed said. “It could have been sufficient for a budding global ecosystem, where life was just beginning.”

The researchers propose that these airborne molecules may have rained down to the surface, delivering crucial biological ingredients directly to land or ocean habitats.

Rethinking Where Life’s First Molecules Came From

“Life likely needed very specific conditions to begin—near volcanoes or hydrothermal vents with complex chemistry,” Browne explained. “We used to think life had to start entirely from scratch, but our results suggest that some of these complex molecules were already widespread under ordinary conditions, which might have made it easier for life to get started.”

Source: SciTECHDaily

Cite this article:

Priyadharshini S (2025), New Evidence Suggests Earth’s Early Atmosphere Helped Ignite Life, AnaTechMaz, pp.1233