Life’s peptide building blocks could have originated in space

The theory of evolution through natural selection forced a paradigm shift in our understanding of biology by creating a framework through which living organisms change over time. Through that lens, we’ve been able to construct vast family trees of plants and animals, tracing them back through billions of years to the earliest lifeforms on our planet. Once we get to the beginning, however, things get more complicated.

One of the enduring questions in science is how life emerged on our planet in the first place. Some support the notion of abiogenesis, in which life emerged from non-living prebiotic chemicals. Others kick the can a little farther down the road, suggesting life emerged elsewhere in the universe and was delivered here when the Earth was young. Increasingly, scientific discoveries are making the case that at least the essential building blocks of life are capable of forming in space.

The near vacuum of molecular clouds — giant gatherings of gas and dust which eventually collapse into stellar systems — turn out to be pretty good gardens for growing some of life’s basic constituent parts. New research by Serge Krasnokutski from the Laboratory Astrophysics Group at the Max Planck Institute for Astronomy, and colleagues, adds peptides to the list of organic molecules which can form in space. Their findings were published in the journal Nature Astronomy.

“We’ve found the formation of biomolecules in different ways before, most commonly through energetic processes. In the Miller-Urey experiments, they provided electric sparks in a glass vessel which leads to the formation of biomolecules,” Krasnokutski told SYFY WIRE. “These energetic processes randomly destroy chemical bonds. It’s not an efficient way to get biological molecules.”

Scientists wanted to find a way to build biomolecules like peptides in an environment resembling the conditions of molecular clouds in space, but there appeared to be a significant barrier. On Earth, the process by which peptides are formed requires first the introduction of water, and then the removal of water in subsequent steps.

Krasnokutski wondered if there was a way to skip the water steps and get to peptides along a different chemical path. To find out, they built an analogue of space in the lab to see what chemical reactions might arise.

“We have a high vacuum chamber which allows us to get to a vacuum state similar to those found in the dense areas of the interstellar medium. Then we have a substrate inside the chamber which is cooled to 10 Kelvin,” Krasnokutski said.

That substrate takes the place of dust particles present in space. The team then deposited carbon monoxide, ammonia, and single carbon atoms — chemicals which are common in the targeted regions of space — onto the substrate where the gases freeze.

“When carbon atoms arrive on the surface of the ice, we see reactions take place. We found they are extremely reactive with almost all molecules we studied, even at this very low temperature,” Krasnokutski said.

Those reactions form aminoketenes, the precursors to peptides, under those conditions. Then, those aminoketenes meet and react forming peptides without needing to go through the complex water reactions previously believed to be necessary.

So far, they’ve been able to form glycine peptides through this process, but Krasnokutski is confident other peptides and even proteins could be formed through similar processes. If that’s borne out it could fill in some of the gaps in our picture of how life formed on Earth.

“The formation of peptides in space would definitely influence the origin of life,” Krasnokutski said. “If those peptides or even proteins can be delivered to the surface of planets, those molecules could trigger the formation of complex organic systems. At this point we’ve found this formation, everything else is speculation.”

We may not be aliens on our own planet, but there’s a possibility that at least some of our most basic parts are extraterrestrial in origin. We don’t know about you, but we think that’s pretty cool.