How Chemistry Becomes Biology

By Ian Cohn
Edited By Timshawn Luh

This past week, a team of scientists from Harvard University, Leiden University, and Kobe University announced what has been since deemed a very exciting discovery—for the first time, the presence of complex organic molecules had been observed in an infant star system. Detected through the use of a complex telescope and detector known as the Atacama Large Millimeter/submillimeter Array, scientists were able to detect the presence of acetonitrile (CH3CN) in a protoplanetary disk surrounding a one-million-year-old star 455 light-years away from our solar system.

This provides yet another clue that our Earth, the only planet currently known to harbor life, may not be as special as we’d like to think. Indeed, while this is the first time a complex organic (carbon-containing) molecule has been observed in a protoplanetary interstellar environment, the presence of complex organic molecules in space is nothing new. Back in 2011, researchers at the University of Hong Kong showed that stars at different phases in their life cycles could produce complex organic compounds (much more complex than acetonitrile) and eject them into space. Other examples of interstellar organic materials exist. Clouds of ethanol, large carbon based molecules called fullerines, and complex organic molecules like pyrene have all been shown to exist in space. This new discovery, then, just adds to the already mountainous pile of evidence that organic chemistry, the basis for life, is not unique to Earth. The easy takeaways: we aren’t anything special, and life may not be some kind of sacred anomaly.

Nonetheless, the question remains—if the chemistry exists, does the biology exist? Or even, how do we get from the chemistry to the biology? In other words, it’s still extremely unclear how the natural world progressed from the isolated reactions of organic chemistry to the complex, biotic (life-containing) systems which characterize biology. Abiogenesis, the natural process of life arising from nonliving matter, remains one of the least understood and most thought provoking questions in modern science. Several theories exist for how life came to exist. One of the more well-known is commonly referred to as the “primordial soup hypothesis,” which posits that the environment of the early Earth had an atmosphere which encouraged the natural synthesis of various organic molecules, and that these reactions eventually increased in complexity until life arose. While this seems like somewhat of a hand-wavy explanation, it does have an important history to it. In 1952, Stanley Miller and Harold Urey took a mixture of gases which would have been present in the atmosphere of the early Earth, simulated other physical and chemical conditions of this environment, and showed that these gases in the “primitive atmosphere” naturally led to the synthesis of over twenty different amino acids, the basic building block of proteins.

Several other models beyond that which was proposed by the Miller-Urey experiment exist, with some building upon the experiment’s principles and others defying them. For instance, the panspermia hypothesis posits that meteoroids and asteroids distributed microscopic life through earth, though this just defers the burden of abiogenesis to another region of space, rather than offer a satisfactory answer to how life first arose. Other theories, classified as “metabolism first” hypotheses, suggest that the chemical reactions underlying metabolism developed first and that life followed, perhaps through the natural formation of protocells (primitive spheres of lipids) to "section off” these metabolic reactions. Yet another set of theories suggest that life began at deep sea vents, known as hydrothermal vents, where hydrogen-rich fluids erupt from the bottom of the ocean and create an environment that increases the concentration of organic molecules, perhaps leading to life.
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Just as the origin of life still remains an open question, so too does the question of whether Earth is the only place in the Universe to truly harbor life. Indeed, mounting evidence suggests that the chemical reactions which underlie biology may not be unique to Earth, but the presence of these reactions in biological systems in places other than Earth remains yet to be discovered.