Critical Questions Concerning the Origins of Life

Understanding the origins of life involves finding answers to a large number of questions. The ten sets of questions outlined below fall into a continuum, beginning with the astrophysical and planetary context of the origins of life, moving on to the development of ever more complex aspects of prebiotic chemistry, and culminating in the assembly of the first cells and the advent of Darwinian evolution, which quickly led to the evolution of increasingly complex forms of life.

1.  What is the range of possible planetary environments? What factors control the dominant geochemical cycles of different planets? How special is the Earth, and our solar system? What constraints can be placed on the time of the earliest possible origin of life on Earth?

2.  What chemical processes shaped the composition of asteroids and comets? How can we explain the diversity of organic compounds present in these primitive bodies? Were stellar ultraviolet fluxes and/or spin-polarized secondary electrons significant in driving the enantiomeric excesses of compounds found in meteorites?

3.  How did the impact history of the early Earth affect the origins of life, both positively and negatively? What were the sources and timing of the accumulation of Earth’s volatiles? What was the composition of the atmospheres of Hadean and Archean Earth, and of Noachian Mars?

4.  What were the geochemical and geophysical contexts of prebiotic synthesis? What minerals would have been present on the early Earth? What role did the photochemistry of the early atmosphere play in the origins of life? Can we explain certain ‘molecular fossils’ as relics of the origins of life on the early Earth?

5.  What prebiotic chemistry was responsible for the synthesis of the building blocks of biology from simple starting materials? Can we define a complete pathway for the prebiotic synthesis of ribonucleotides, oligonucleotides and RNA? How were fatty acids and other membrane-forming amphiphiles synthesized? Were amino acids and peptides generated alongside ribonucleotides and lipids? Of the many possibilities, what actual mechanisms led to homochirality in prebiotic synthesis?

6.  Regarding systems chemistry on the early Earth, what principles or methods can help us understand the chemistry of realistically complex mixtures of reactants? When does chemical complexity help and when does it hurt?

7.  Can the fast and accurate non-enzymatic and/or RNA-catalyzed replication of RNA be demonstrated experimentally? How would RNA fitness landscapes constrain the evolution of RNA catalysts (ribozymes)? How would such fitness landscapes be affected by their chemical environment? Are there alternatives to RNA that could have acted as the central biopolymer of primitive cells?

8.  How did primitive protocells assemble and replicate? What physical mechanisms drove the growth and division of the earliest protocell membranes? How was the replication of genetic polymers, including RNA, affected by encapsulation within protocell membranes?

9.  How did prebiotic synthetic processes morph into genetically encoded metabolic pathways? How can we explain the origins of biological catalysis in the chemistry of the early Earth? How did the complex process of genetically encoded peptide synthesis emerge, step by step? What is the origin of the genetic code?

10.  What is the earliest record of microbial life? How can geochemistry constrain the timing and environments of the origin and early evolution of life? What can deep phylogeny tell us about the history of life prior to the last common ancestor?

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