Crucial building blocks for life on Earth can form more easily in space, new research says

The origins of life on Earth are still mysterious, but we are slowly unraveling the steps and necessary ingredients. Scientists believe that life emerged in a primordial soup of organic chemicals and biomolecules on early Earth, eventually giving rise to real organisms.

It has long been suspected that some of these ingredients may have been brought in from space. Now it appears from a new study, published in Scientific progressshows that a special group of molecules known as peptides can form more easily under the conditions of space than those on Earth. That means they could have been brought to the early Earth by meteorites or comets – and life could possibly form elsewhere too.

The functions of life are maintained in our cells (and those of all living things) by large, complex, carbon-based (organic) molecules called proteins. How we make the wide variety of proteins we need to stay alive is encoded in our DNA, which is itself a large and complex organic molecule.

However, these complex molecules are composed of a variety of small and simple molecules, such as amino acids – the so-called building blocks of life.

To explain the origin of life, we need to understand how and where these building blocks form and under what conditions they spontaneously self-assemble into more complex structures. Finally, we must understand the step that allows them to become a limited, self-replicating system: a living organism.

This latest study sheds light on how some of these building blocks may have formed and assembled, and how they ended up on Earth.

Steps to life

DNA consists of about twenty different amino acids. Like letters of the alphabet, these are arranged in various combinations in the double helix structure of DNA to encode our genetic code.

Peptides are also a collection of amino acids in a chain-like structure. Peptides can consist of just two amino acids, but can also consist of hundreds of amino acids.

The assembly of amino acids into peptides is an important step because peptides provide functions such as ‘catalyzing’ or enhancing reactions that are important for sustaining life. They are also candidate molecules that could have been further assembled into early versions of membranes, trapping functional molecules in cell-like structures.

However, despite their potentially important role in the origins of life, it was not so easy for peptides to form spontaneously under the environmental conditions on early Earth. In fact, the scientists behind the current study had previously shown that the cold conditions of space are actually more favorable for the formation of peptides.

In the very low density of clouds of molecules and dust grains in a region of space called the interstellar medium (see above), individual carbon atoms can stick to the surface of dust grains along with carbon monoxide and ammonia molecules. They then react to form amino acid-like molecules. When such a cloud becomes denser and dust particles also start to stick together, these molecules can combine into peptides.

In their new research, the scientists look at the dense environment of dusty disks, from which a new solar system with a star and planets ultimately emerges. Such disks form when clouds suddenly collapse under the influence of gravity. In this environment, water molecules are much more common: they form ice on the surface of growing agglomerates of particles that could inhibit the reactions that form peptides.

By mimicking the reactions likely to occur in the interstellar medium in the laboratory, the study shows that while the formation of peptides is somewhat reduced, it is not prevented. Instead, as rocks and dust come together to form larger bodies such as asteroids and comets, these bodies heat up and can form liquids. This stimulates the formation of peptides in these fluids, and there is a natural selection of further reactions that result in even more complex organic molecules. These processes are said to have taken place during the formation of our own solar system.

Many of the building blocks of life, such as amino acids, lipids and sugars, can form in the space environment. Many have been discovered in meteorites.

Because the formation of peptides is more efficient in space than on Earth, and because they can accumulate in comets, their impact on early Earth may have delivered a charge that accelerated the steps toward the origin of life on Earth.

What does all this mean for our chances of finding extraterrestrial life? Well, the building blocks for life are available everywhere in the universe. How specific the conditions must be to allow them to self-assemble into living organisms is still an open question. Once we know that, we have a good idea of ​​how widespread life may or may not be.