Answer to Question #93634 in Evolution for Ella

Question #93634
How did life begin on earth?
Expert's answer

According to modern models, life on Earth arose about 4.1-3.8 billion years ago. Chemical evolution is the first stage in the evolution of life, during which organic, prebiotic substances appeared from inorganic molecules under the influence of external energy, selection factors, and self-organization processes that are present in all complex systems consisting of carbon-containing molecules. It is accepted that all monomers of biomolecules (i.e., nucleotides, amino acids, lipids) were formed during the process of chemical evolution. It is assumed that the first living creatures were RNA organisms without proteins and DNA. The discovery of ribozymes suggested that the first RNA molecules could catalyze their self-replication and produce their copies. As a result, the next stage of the emergence of life on Earth is characterized by the presence of ribonucleic acid molecules that possess two functions - storing genetic information and catalysis of chemical reactions. Therefore, RNAs could exist entirely autonomously, catalyzing metabolic reactions, the synthesis of new ribonucleotides and self-reproducing, retaining catalytic properties from generation to generation. The accumulation of random mutations led to the appearance of RNAs that catalyze the synthesis of specific proteins, which are more effective catalysts while the mechanisms of natural selection fixed these mutations. On the other hand, specialized repositories of genetic information in the form of DNA appeared. Formation of the lipid-containing membranes around the replication factories could improve the primitive metabolic process serving as an example of the first biological cells. 

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