All life on Earth is thought to have emerged from the “primordial soup,” a chemical cocktail mixed 3.9 billion years ago whose recipe scientists are still trying to figure out. A study published Monday in the journal Astrobiology showed that at least one of those life-potentiating ingredients was less than ideal. Much as we might like to think the primordial soup was some sort of magical elixir, we now know that it was probably just a puddle that smelled like farts.
In the study, the team, led by Massachusetts Institute of Technology postdoc Sukrit Ranjan, Ph.D., looked to validate the claims of a 2015 Cambridge University study showing that the precursors to RNA — itself a precursor to DNA, considered the fundamental building block of earthly life — could be synthesized using only three ingredients. One of those ingredients was hydrogen sulfide, the sulfur-based compound that makes rotten eggs so dank. Though the recipe the Cambridge scientists came up with was compelling, there was one issue: Nobody knew whether the ingredients, especially hydrogen sulfide, were available on Earth at the time.
What Ranjan and his team did was painstakingly recreate computer models of the violently hot, oxygen-free Earth that existed 3.9 billion years ago, previously determined as the time when life emerged. Through those models, they showed that some smelly sulfur-containing compounds — namely, sulfites and bisulfites — definitely would have accumulated in high enough concentrations, thanks to the explosive volcanic activity that characterized the era.
“In shallow lakes, we found these molecules would have been an inevitable part of the environment,” Ranjan, part of MIT’s Department of Earth, Atmospheric and Planetary Sciences, told MIT News. “Whether they were integral to the origin of life is something we’re trying to work out.”
Ranjan’s team used a volcanism model to determine what gases were being spewed into the air and a geochemistry model to figure out how those gases dissolved into the water below. The volcanoes at the time, they discovered, spewed up loads of hot sulfur dioxide and hydrogen sulfide, the latter of which easily dissolved in pools of shallow water to form sulfidic anions, sulfites, and bisulfites. They reasoned that larger bodies of water wouldn’t be able to build up sufficiently high concentrations of chemicals for a potentially life-creating reaction to take place.
Those sulfites and bisulfites, according to Ranjan and the Cambridge scientists who worked on the 2015 paper, would probably have helped kickstart the reactions that led to the creation of RNA. Smelling like hell would have just been an unfortunate side effect.
These days, we still encounter sulfites and bisulfites, though encountering them now isn’t as fortuitous for humans as it might have been at the dawn of life. Sulfites (in the form of sulfur dioxide), and occasionally bisulfites, are often added in small amounts to wine as preservatives, but they are generally frowned upon, as they’re associated with allergies in some people and can even be identified by sensitive noses.
Sulfites and bisulfites may have been the stankiest ingredients (as far as we know) of the primordial soup, but they’re far from the only ones. Scientists believe that the mixture must have also contained the precursors to proteins, nucleotide chains, and lipids, which are the basic building blocks of the cell. In 2017, a different team discovered the soup’s tiny “fairy godmother” molecule, DAP, which is thought to have facilitated important reactions necessary for life. The research in this field continues to show that, despite how wondrous and rich (and mostly fair-smelling) life on Earth now appears to be, its beginnings were extraordinarily humble.