Cyanide may have aided the emergence of life on Earth, according to scientists, in a discovery that may hold hints to life on other worlds. According to a new study, despite its reputation as a deadly and lethal gas, the chemical compound may have aided in the initial events that led to life on Earth. Chemists found how cyanide could have facilitated chemical reactions that metabolize carbon dioxide in the absence of the sophisticated proteins required by living creatures today.
Cyanide, a colorless and lethal gas, is today renowned as a fast-acting poison and a chemical weapon. However, four billion years ago, it could have been a sign of life. Scripps Research chemists have demonstrated for the first time how cyanide may have enabled some of the earliest metabolic reactions to produce carbon-based molecules from carbon dioxide. This revelation not only improves scientists’ understanding of the evolution of life on Earth, but it also provides insight into the potential chemistry of life on other planets.
The researchers demonstrated that the chemical molecule, which consists of a carbon atom bound to a nitrogen atom, could have facilitated some of the early metabolic events on Earth that produced carbon-based chemicals from carbon dioxide. Metabolic reactions are reactions that create energy out of food and are essential for sustaining life.
We base our search for indications of life, whether on early Earth or on distant worlds, on the biochemistry we know exists in life today. It was frightening how straightforward it was. We didn’t have to do anything extra; we just brought these molecules together, waited, and the reaction happened spontaneously.
Ramanarayanan Krishnamurthy
“We base our search for indications of life, whether on early Earth or on distant worlds, on the biochemistry we know exists in life today. The fact that cyanide may drive these same metabolic events highlights how life can be extremely different “Ramanarayanan Krishnamurthy, PhD, an associate professor of chemistry at Scripps Research and main author of the new Nature Chemistry research, says.
Some bacteria on Earth today use a sequence of chemical reactions known as the reverse tricarboxylic acid cycle (r-TCA cycle) to convert carbon dioxide and water into chemical molecules required for life. Many scientists believe that the r-TCA cycle happened on the early Earth’s surface to produce chemicals required for life. The only drawback is that today’s r-TCA cycle relies on a collection of sophisticated proteins that did not exist before life emerged. Researchers have demonstrated that, four billion years ago, in the murky primordial soup, certain metals may have triggered the same processes without today’s proteins, but only under extremely acidic and hot circumstances not thought to be prominent on early Earth.
Krishnamurthy and his colleagues wondered if a different chemical could cause the same reactions under more benign settings. They knew cyanide was prevalent in the early Earth’s atmosphere and began speculating on a series of reactions that could have employed cyanide to generate organic molecules from carbon dioxide. The reactions were then tested in a test tube. It functioned because cyanide took the place of proteins or metals in transporting electrons between molecules.
“It was frightening how straightforward it was,” Krishnamurthy adds. “We didn’t have to do anything extra; we just brought these molecules together, waited, and the reaction happened spontaneously.”
Unlike prior r-TCA versions that utilised metals, the cyanide-based cycle performed at room temperature and over a wide pH range, mimicking what was likely present on the early Earth.
Furthermore, the researchers demonstrated that cyanide enabled an even simpler version of the r-TCA cycle, one that avoided several of the stages and less-stable intermediate intermediates seen in the contemporary cycle. According to Krishnamurthy, this subgroup of responses may have preceded the whole r-TCA cycle in the genesis of life.
He argues that there is no way to prove without a shadow of a doubt what chemistry transpired on the early Earth. However, the discovery of a new set of reactions opens the door to a new set of hypothetical conditions that may be compatible with life. And this has ramifications for the hunt for life on Earth, both in the past and in the future.
“It frees us from having to say there must be these metals and these harsh conditions,” Krishnamurthy explains. “This cyanide-based chemistry could lead to the evolution of life.” “It was frightening how straightforward it was,” Krishnamurthy remarked. “We didn’t have to do anything extra; we just brought these molecules together, waited, and the reaction happened spontaneously.”
Although the experiment does not provide clear confirmation that cyanide was engaged in this process on early Earth, the researchers say it does provide a new way of thinking about the beginning of life and, possibly, a new way of searching for life on other worlds.
