Scientists from the University of Colorado at Boulder and NASA have shown that biomolecules like sulfur could have formed in Earth’s atmosphere and rained down, providing sufficient biological support to facilitate the origin of life.
The researchers behind the potentially historic discovery suggest that understanding these types of processes could reveal the evolution of all life on Earth and aid the search for life in the cosmos.
“We used to think life had to start completely from scratch,” explained the study’s senior author, Ellie Browne, a chemistry professor and a CIRES fellow, “but our results suggest some of these more complex molecules were already widespread under non-specialized conditions, which might have made it a little easier for life to get going.”
On Earth, where the only known living organisms exist, biomolecules such as carbon and sulfur are irreplaceable ingredients without which life would not exist. For example, these biomolecules form amino acids, which are often referred to as the ‘building blocks’ of proteins.
Still, scientists have struggled to determine how biomolecules such as carbon and sulfur were formed on Early Earth. According to a statement detailing the CU at Boulder team’s research, scientists had previously assumed that biomolecules emerged after life emerged “as a product of a living system.”
This theory was supported by early Earth simulations that failed to find meaningful amounts of sulfur biomolecules before the advent of the first life forms, or under specialized conditions that the team said were “unlikely to be widespread” on our planet. So, when scientists using the James Webb Space Telescope spotted the biomolecule dimethyl sulfide around a distant exoplanet, it was hailed by some as a potential sign of life beyond Earth.
More recently, Brown and the latest study’s first author, Nate Reed, a postdoctoral fellow at NASA, who conducted the work as a postdoctoral researcher in the Department of Chemistry and the Cooperative Institute for Research in Environmental Sciences (CIRES) at CU Boulder, conducted experiments where they were able to create dimethyl sulfide in the lab with common atmospheric gasses and light. The team said the result “suggested that this molecule could arise in places void of life.”
To estimate the concentrations of biomolecules contributed by the atmosphere above an early, lifeless Earth, the team designed a series of experiments simulating the planet’s nascent atmosphere. After settling on a gas mixture containing nitrogen, carbon dioxide, methane, and hydrogen sulfide, the team exposed the simulated ‘atmosphere’ to a light simulating the Sun.
When the researchers measured the early Earth atmosphere in their model with a highly sensitive mass spectrometer designed to identify and quantify individual chemical compounds, they found “a whole suite” of sulfur-based biomolecules. These artificially created biomolecules include coenzyme M, which they described as “critical for metabolism,” and the amino acids taurine and cysteine.
Next, Reed and Browne scaled the biomolecule concentrations from their artificial early Earth atmosphere to estimate how much cysteine the planet’s entire atmosphere could have produced. Those calculations determined that about one octillion (one followed by 27 zeros) cells could be supplied. For comparison, Earth currently contains roughly one nonillion (one followed by 30 zeros) cysteine cells.
Reed said that although their simulated atmospheric biomolecule concentrations were well below the measured levels, it was still “a lot of cysteine,” given that Earth was still devoid of life.
“It might be enough for a budding global ecosystem, where life is just getting started,” the researcher said.
When discussing the role these atmospheric biomolecules could have played in the formation of life in Earth, Browne conceded that life “probably required some very specialized conditions to get started.” As examples, the researcher pointed to extreme environments with “complex chemistry,” such as near volcanoes or hydrothermal vents.
While the exact origin of life remains a mystery, Browne said his team’s discovery could “help us understand the evolution of life at its earliest stages.”
The study “An Archean atmosphere rich in sulfur biomolecules” was published in Proceedings of the National Academy of Sciences.
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.