Protocell development within evaporating lakes on the early Earth

Abstract

My research addresses the problem of how the first cells assembled from non-living material in the early Earth environment by testing whether putative components of the first cells could have assembled within evaporating lakes on the early Earth. Evaporation concentrates dissolved solutes, potentially converting chemical precursors into the membranes and biopolymers of the earliest cells. The first cell membranes may have been composed of fatty acids, and I have characterized plausible sources of membrane-forming fatty acids on the early Earth. The first peptides may have been formed during evaporation and subsequent dehydration of lakes filled with environmentally available amino acids, and I have shown that fatty acid membranes do not inhibit peptide formation during dehydration. I have also shown that these fatty acid membranes retain their encapsulated contents in salty water following partial evaporation from the lake; however, complete dehydration disrupts encapsulation by the membranes. Additionally, I have shown that fatty acid membranes retain encapsulated contents when exposed to cold temperatures below the membrane melting transition; cold temperatures are beneficial during the synthesis of RNA genomes. All of the work above, which has been published in academic journals, appears in Chapters 1 through 4 of this dissertation. In Chapter 5, I describe unpublished findings about RNA assembly and membrane encapsulation in natural carbonate lakes, modern analogs for locations that may have enabled the origin of life on early Earth. I have also described unpublished observations using size-exclusion chromatography of fatty acid vesicles that I hope will facilitate future research in this area. Taken together, my dissertation research results support the hypothesis that membranes and biopolymers developed together into the first cells within evaporating lakes on the early Earth.