I’m still plowing through my notes on the 2019 Astrobiology Science Conference (AbSciCon, June 24-28, Bellevue, Washington). Here are some tidbits from a session on “unresolved issues” in origins of life research.
Someone, whose name I regrettably did not write down, said in introducing this session that only three percent of reactions run by professional chemists since 1771 have been run for more than two days. What does this mean? It means that scientists might be missing something…. In understanding prebiotic chemistry and how it led (or leads) to the chemistry of life, we’ve learned so much but have yet to be able to explain how life began on Earth (and how life might have began elsewhere).
Open questions in origins of life research include: What is life? (There is no consensus definition.) What is the origin of life? (We don’t know yet. Theories abound.) Is the origin of life easy or hard? Is the origin of life frequent or rare? Is the origin of life a unique process, or are there many pathways to go from nonlife to life? Are there different classes of life? Where is life possible? That is, in what environments might life be possible?
And what about the possibility of life beyond Earth? What is the current search space? In looking for signs of life, we’re restricted to a small segment of our own galaxy. The Milky Way resides in the Laniakea galaxy supercluster, which includes another 100,000 galaxies. And this is just a tiny sliver of the observable universe. So, astrobiologists have plenty of work to do for the next few centuries, at least.
For now, astrobiologists are interested in exploring abiotic and prebiotic chemistry in solar system environments, including Earth environments, to compare with lab experiments in abiotic and prebiotic chemistry. The aim is to determine whether terrestrial abiotic and prebiotic chemistry is “universal” or unique to Earth. We don’t know.
NASA Goddard Space Flight Center astrobiologist Jamie Elsila noted at the AbSciCon session that in studies of prebiotic chemistry in the solar system, analyses of carbonaceous chondrites—making up less than 5 percent of meteorites collected on Earth – have dominated the literature on the topic for 30 years. The Murchison meteorite, recovered in Australia in 1969, weighing in at 220 pounds, has been a particular focus of study. However, Elsila said, “Murchison is neither unique nor representative.”
In other words, many pieces of the puzzle to be solved could be missing….
Eric Smith of the Georgia Institute of Technology and the Environmental and Life Sciences Institute (Tokyo) observed that “this is still really early days” in origins of life research. His description of the origin of life? “A cascade of non-equilibrium phase transitions in planetary geochemistry.” He said that the fact that scientists are growing further away from, rather than closer to, consensus on a theory of the origin(s) of life is a bit of a relief. Answering the question, what is the origin of life?, will require that researchers “become theorists of the complex in ways that are completely new.”
Jamie Elsila acknowledged that different astrobiologists use the term “complexity” in different ways. “It means different things in different contexts and different conversations.” (So, there’s complexity to complexity….)
Nick Hud of the NASA-National Science Foundation-funded Center for Chemical Evolution (CCE), based at Georgia Tech, said at the session that the assumptions guiding the CCE’s origins of life research over the past 10 years are that “life is based on biopolymers,” that the “emergence of biopolymers was essential to the origin of life,” and that molecules and reactions that gave rise to biopolymers “were simple and robust.” (Okay, if you find this confusing, check out the title of a recent paper by Hud’s group, published in the Proceedings of the National Academy of Sciences (PNAS): “Selective incorporation of proteinaceous over nonproteinaceous cationic amino acids in model prebiotic oligomerization reactions.”)
In another session at AbSciCon, Reggie Hudson, lead scientist for the Cosmic Ice Laboratory at NASA’s Goddard Space Flight Center, said that some organic chemical reactions appear to be “unstoppable” throughout the solar system – for example, on Saturn’s moon Titan, and on the dwarf planet Pluto. His advice to astrobiologists? “Seek and ye shall find rings” – that is, the ring structures of hydrocarbon molecules (which could be prebiotic or biotic).
To wrap up, origins of life research is complicated – and deeply interesting.