Biology 1402Chapter 15 Tracing Evolutionary HistoryThe photosynthetic cyanobacteria that produced the stromatolites were probably preceded by simpler non-photosynthetic life-forms, and therefore an even earlier period of prokaryote evolution.Miller and Urey, scientists in 1950’s, were not attempting to replicate the conditions of the early Earth or generate life from nonlife, just to help fill in one gap in scenarios about the origins of life on a prebiotic Earth.The steps of origin of life from nonlife early in Earth’s history to most recent are: abiotic synthesis of small organic molecules, formation of proteins and nucleic acids, formation of protocells and lastly, the origin of self-replicating molecule of inheritance. The first polymers were produced by dripping dilute solutions of amino acids or RNA monomers onto hot sand, clay and rocks. The heat vaporizes the water and concentrates the monomers.
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