Fig. 3

Early evolution of life on Earth. Life originated from prebiotic chemistry. First stages of cellular evolution may have included replicative polymers other than DNA and RNA; the RNA world refers to a time when the RNA molecule acted as the hereditary as well as catalytic molecule of cells; eventually, RNA chemistry originated proteins (a relic from these days is the RNA-mediated synthesis of proteins in extant ribosomes); it is thought that cells capable of synthesizing proteins were selected for having superior catalytic molecules; finally, protein chemistry-originated DNA and cells with DNA genomes were selected for having a more stable hereditary molecule; the last universal common ancestor or cenancestor was very likely similar to extant cells in their metabolic and hereditary capacities