Ever since Haldane and Oparin first proposed the idea of a chemical origin to life, scientists have puzzled over how life arose on a primordial earth. The idea that life can arise from non-living material was given credibility by the the famous Miller-Urey experiments which replicated conditions on a primordial Earth and showed that organic molecules could be created. Life on Earth may also be of an extraterrestrial origin since organic molecules which are commonly found on Earth have been found in our solar system as well as in the far reaches of space. A varying complexity of organic molecules from simple ammonia to more complex hydrocarbons have been identified in our solar system as well as in the far reaches of space. All of this lends credibility to the idea that life might have started from non-living material. However, what remains poorly understood is whether the organic precursors to early life were seeded from interstellar material during planet formation or whether it was an independent process on Earth following that event.
Here, the Meierhenrich group describes the identification of ribose and other structurally similar sugars after subjugating samples containing ice, methanol and ammonia to ultraviolet radiation. Ribose is one of the major constituents of ribonucleic acids (RNA). RNA is closely related to DNA and both are essential components of life along with proteins and carbohydrates.
The experiment was done in order to simulate the conditions expected during the early formation of the solar system. Nebulas consisting of dust, ice, helium, hydrogen and a mixture of other gases provide the starting material for solar systems. During solar system and planetary formation, the mixture of particles in the nebula are subject to ultraviolet light and cosmic radiation which can result in complex chemistry. The researchers used a process called mass spectrometry to identify a diverse range of molecules in the experimental samples. It’s not terribly important to understand what mass spectrometry is; all you need to know is that it is a method capable of characterizing atoms or molecules and their structures based on mass and charge. They showed a diverse assortment of different types of sugars, alcohols, molecules with long chains, and cyclic molecules all of which are important to life. Of particular importance to researchers was the identification of ribose in the treated samples.
RNA is involved in many biological processes including functioning as a genetic code and mediating the regulation and expression of genes. RNA is thought to predate DNA but its origins remain unknown since the chemistry of the formation of ribose itself is complex. In this study, the Meierhenrich group shows that it is possible for such molecules to be synthesized in conditions that resemble the late stages of solar system formation. .It is not too farfetched to think these biological molecules, if present before formation of the Earth, could have been the building blocks of life.
The panspermia hypothesis is a theory that life exists throughout the universe as a result of being distributed by asteroids, meteoroids and comets. Intelligent civilizations elsewhere in the universe could have also intentionally or not (microbes hitching rides on UFOs) introduced life to our planets during their visits? Sounds crazy but that’s another extension of the panspermia hypothesis.
Photo credit: NASA, ESA, and M. Livio, The Hubble Heritage Team and the Hubble 20th Anniversary Team (STScI)
Meinert, C. et al. Ribose and related sugars from ultraviolet irradiation of interstellar ice analogs. Science (80-. ). 352, 208–212 (2016).