Last Thursday, Dartmouth physics professor Marcelo Gleiser crossed disciplinary boundaries to give a lecture at the Chemistry Department Colloquium called, “The Chirality of Life: From Phase transitions to Astrobiology.” Gleiser, who holds a “wide-ranging interest in physics in cosmology and theoretical physics,” is a prolific contributor to domestic and international publications and an author of three popular books on cosmology and religion, A Tear at the Edge of Creation (2010), The Prophet and the Astronomer (2002), and The Dancing Universe (1997).

 

Gleiser began with the pitch that astrobiology concerns matters that should pique the interests of members of various disciplines, including physicists, chemists, and astronomers. Life as we know it is composed of pure polymers, many of which hold the chemical character of chirality—the lack of internal plane of symmetry which bestows the molecule with functional uniqueness from its other possible isomers. Gleiser presented how chirality could be seen as a method to study life in Earth as well as a way to predict possible life in other planets.

 

Life—defined by NASA as “a self-sustaining chemical reaction network capable of Darwinian evolution”—on planet earth has risen from a common theme of interactions between oxygen, sulfur, nitrogen, and carbon, the last of which offers chemical versatility to promote the richness of life that we see around us. Biologists believe that liquid solvent was needed to sustain a chemical cataclysm, and that evidence of life could be found stretching back to 3.5 to 3.8 billion years ago. Gleiser noted that the pinpointing the near-exact timeframe was crucial because “the sooner life appeared in our own world, the most probable life is to occur in other places.”

 

Gleiser presented two current models of thought regarding life’s origins, warning beforehand, “We will never be able to know exactly how life came on earth; only viable models.” One such model, proposed by Stanley Miller and Harold Urey, hypothesized that the right building blocks and an energy source could potentially synthesize amino acids. Another model, which is grounded on the disputed finding that amino acids have been found in asteroids, hypothesizes that life emerged from outer space.

 

Despite their differences, the two models both agree that amino acids are a fundamental building block of life as we know it.  Gleiser pointed at the chemical nature of amino acids, that amino acids are “left-handed,” and raised the question of how the chiral characteristics of life could have emerged.

Gleiser presented two main hypotheses. The Asymmetric Autocatalytic Reaction-Rate model, presented in 1953, provided a “simple and sufficient life model” for the evolution of organic molecules from a small initial imbalance. On the other hand, Punctuated Chirality, yet another model, suggests that chirality of amino acids originated from the fact that the history of earth was full of disturbances. Each new disturbance reset the initial and potential life forms to different adaptability conditions.

 

Gleiser concluded with his own statements that effects from small bias seem irrelevant to determine chirality and sided with Punctuated Chirality. Gleiser concluded with the suggestion that environmental effects may have a far greater role in triggering chiral choice, further bolstering the uniqueness of life on Earth as just one of many possible chemical iterations of life, rooted in chance and circumstance.