There is almost no geological record of what happened on our planet during the first half billion years after its formation. In the absence of detailed information, we can only speculate by exploiting our present knowledge on organic chemistry and biochemistry and by considering other celestial bodies which share common characteristics with primitive Earth. Prebiotic molecules are species which are simple enough to be formed in abiotic processes but contain the functional groups typical of biological molecules or have the capability to easily evolve into them. Seminal work by Oparin and Miller is at the base of the so-called endogenous synthesis theory. Yet, it is not clear how the necessary massive organic synthesis up to very complex species could occur in a water-dominated environment. The alternative theory of exogenous synthesis is supported by the identification of organic molecules (complex to some extent) in comets, asteroids, meteorites and even interplanetary dust particles. According to this theory, prebiotic molecules were synthesized in the cloud from which the Solar System originated. In the periphery of the newly born Solar System, comets and meteorites were able to preserve them, being far away from the intense emissions of photons and energetic particles by the young Sun. Finally, comets and meteorites falling on our planet would have brought those prebiotic molecules to the already cooled-down Earth. In support of this hypothesis, there is the observation of many prebiotic molecules in the interstellar clouds, including solar-type star-forming regions: amongst the almost 300 molecules identified in the interstellar medium (the space between solar systems of our Galaxy), only a few tens do not contain carbon atoms and many prebiotic species (e.g. glycolaldehyde, cyanoacetylene, formamide) have been identified.

The comprehension of the chemical processes that lead from simple atomic/diatomic species to prebiotic complex chemicals is an important part of the study on the origin of life. The study of these preliminary steps might seem relatively simple compared to the characterization of the other unknown phenomena that have led to the first living organisms. Nevertheless, the formation mechanisms of many of the prebiotic molecules that we observe nowadays in proto-stellar clouds or comets/meteorites or planetary atmospheres are far from being understood, while a comprehension of those processes can certainly help to set the stage for the emergence of life to occur. The aim is to reconstruct the chemistry that preceded the emergence of life, the first important piece in this complex puzzle. And once we have clarified how easy (or difficult) it is to provide the massive organic synthesis that precedes life in planets similar to primitive Earth, we can gain a better insight of how probable this event is elsewhere.

In this webinar, I will present the status of our knowledge on the gas-phase chemistry occurring either in star-forming regions of the interstellar medium or in the upper atmosphere of Titan (the massive moon of Saturn) and leading to relatively complex organic molecules.