As near as we can tell, our planet is about 4.5 billion years old. It was a wildly inhospitable place in the early eons, with frequent asteroid impacts and a choking atmosphere of carbon dioxide, ammonia, and methane. Yet, life found a foothold after just a few hundred million years, and the chemical reactions that led to the emergence of life are the subject of much research. Scientists from MIT and the Harvard-Smithsonian Center for Astrophysics have undertaken a project to replicate the conditions of Earth four billion years ago, with an emphasis on Earth sciences, in hopes of better understanding the chemical origins of life.
Before Earth developed even the simplest single-celled organisms that evolved to become all the life present today, there was chemistry. At some point, organic molecules like amino acids and RNA formed that could form the basis for biological life. Researchers have worked for years to discover how this happened, and some recent work on ancient Earth may have pointed us in the right direction. In the new MIT/Harvard study, the researchers are looking at the effect of a class of molecules called sulfidic anions.
Work done in 2016 suggested that high volcanic activity on Earth between 3.9 and 4 billion years ago may have spread sulfur dioxide throughout the atmosphere. The sulfur would have eventually settled in water as sulfidic anions (specifically sulfites and bisulfites). This potentially sidesteps one of the problems with current thinking on the chemical origins of life. In 2015, a team of researchers showed it was possible to synthesize RNA precursors with hydrogen cyanide, hydrogen sulfide, and ultraviolet light. That would all have been readily available on Earth at the time. However, hydrogen sulfide would have remained mostly in the atmosphere rather than building up in water (this is where Earth sciences come in). Those sulfidic anions, however, could potentially serve the same chemical role.
Using a model of ramped up volcanic activity on Earth, the researchers determined that sulfidic anions could have built up to significant concentrations in water similar to those used in the laboratory. Next came an analysis of these chemical components to see if they could generate biological molecules. The team succeeded in creating ribonucleotides (the base pairs of RNA), and the process was surprisingly efficient. The molecules formed with sulfidic anions 10 times faster than with hydrogen sulfide.
So, the application of planetary science to study the origin of life may have set us on the right track. We know the reactions work in the lab, but more work is needed to confirm the findings. The team is conducting more research to establish the presence of sulfidic anions on Earth billions of years ago.
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