We are all stardust — but how that stardust became life on Earth is a mystery. The complexity of just one of your cells, where small proteins walk carrying cargo on their backs and enzymes zipping along your DNA to read out the instructions is vast and unknown.
But scientists do you have a theory? for how this all started, and it starts with DNA’s cousin, RNA. These fibrous molecules are made up of compounds called nucleotides and are responsible for delivering genetic messages and building proteins. Their single-stranded structure, unlike DNA’s double strands, makes them less stable and easier to assemble — possibly easy enough to arise from the mix of molecules that appeared on the Earth’s surface some 3.8 billion years ago. simmer.
Now scientists have found more ingredients for that stew in a gas cloud toward the center of our galaxywhich provides further clues as to what kind of molecules there might have been to form the first life on Earth.
What’s new – In the new studyresearchers scanned a cloud of gas more than 27,000 light-years away looking for compounds called nitriles. These molecules have complex chemistry and are involved in the reactions that form the building blocks of RNA. They also more than likely form the basis of your healthcare provider’s gloves and other personal protective equipment.
The researchers identify six nitriles for the first time in an area of one of the largest molecular clouds in the center of our Milky Way galaxy, aptly named G+0.693-0.027. These nitriles play a role in the formation of molecules that are crucial to life, or biomolecules, such as nucleotides (the basis of genetic material), lipids (fats) and amino acids (the building block of proteins).
“We definitely needed nitriles to form biomolecules on early Earth, so the fact that nitriles were found in space shows how widespread the foundation for life is in the universe,” he said. Thomas Carell† Carell is professor of organic chemistry at the Ludwig Maximilian University of Munich. Carell was not involved in the recent investigation.
The results were published on Friday 8 July in Frontiers in astronomy and space science†
How they did it – Nitriles are a diverse group of molecules, but they all contain a carbon atom bonded to a nitrogen atom. This is one of the most common bonds in life’s chemistry — but it’s less common in the gas clouds around the center of the Milky Way.
The researchers spent hundreds of hours collecting data from the G+0.693 cloud using two radio telescopes in Spain, the Yebes 40 meters and IRAM 30 meters telescopes. They used a method called molecular spectroscopy to identify signatures of specific molecules in the cloud.
When light passes through or around an object or material in space, the composition of that object changes the qualities of the light. These characteristics can then be used to decipher the composition of the material. Each molecule has a distinctive pattern, almost like a fingerprint, that radio telescopes can detect when tuned to the correct frequency range.
The signals that nitriles give off are very weak compared to other molecules in the cloud, such as carbon monoxide and ammonia, says Victor Rivilla, one of the study’s co-authors. Technological innovation has only recently made it possible to detect these distant molecules, he says.
“If we want to detect them, we need very sensitive and deep observations,” Rivilla says. He is an astronomer at the Center for Astrobiology of the Spanish National Research Council.
Rivilla and his team identified four nitriles (cyanuric acid, cyanosole, propargyl cyanide and cyanopropyne) with a high degree of certainty as being in the cloud, and tentatively also identified two others (cyanoformaldehyde and glycolonitrile).
Why it matters – This one it’s not the first time that astrophysicists have found nitriles in this particular cloud. But each new discovery expands what we know is possible. These molecular clouds are an ‘impressive chemical reactor’, says Gregoire Dangerwho specializes in prebiotic chemistry at the University of Aix-Marseille in France and was not involved in the new study.
“This work is a new example of the molecular diversity generated in such an environment,” he says.
By mapping the molecular diversity of the primordial space cloud, we can understand the ingredients that may have gone into the “primordial soup” from which life on Earth emerged – and possibly elsewhere in the galaxy†
Here’s the timeline:
- About 4.5 billion years ago, planet Earth was formed, probably from the debris left over from the sun’s birth.
- About 3.9 billion years ago, Earth was ravaged by asteroids – some of which may have been carried along molecules such as nitriles that could help form the earliest building blocks of life.
- Just under 100 million years later, the first life forms began to appear on our planet.
There are empty spaces in this timeline for millions of years. The journey from molecular cloud to asteroid to nascent Earth would likely change every molecule significantly, so we can’t point to nitriles in space and assume they would have arrived on Earth that way, Danger points out.
What’s next – To fill in the gaps in our origin story, scientists will continue to look for other molecules that may have been precursors to life.
“There are still important missing molecules that are difficult to detect,” Rivilla says.
He and his team plan to expand their interstellar search for other basic ingredients that would have been needed to make RNA and eventually evolve into the first living cells.
“We are also studying the chemical contents of other molecular clouds at the center of our Milky Way, as well as other regions where stars and planets are formed,” he says.
Each new discovery will help us understand how the limited chemistry available on Earth has been able to create the complexity around and within us.
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