The appearance of self-replicating molecules, such as RNA or similar nucleic acid analogues, signified a monumental leap towards life. These molecules had the ability to store genetic information and catalyze their own replication, laying the foundational mechanism for heredity and evolution by natural selection, driving the complexity forward towards the emergence of life as we understand it. While none survive today, viruses are an interesting related non-life thing. Another interesting and related thing in modern life are plasmids and transposons. In bacteria and some other organisms, these DNA molecules replicate independently of the host’s chromosomal DNA. While they are part of complex cellular life and rely on the cell’s machinery for replication, their ability to replicate independently echoes the autonomy of early self-replicating molecules.
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Big History Thresholds: 1=Big Bang | 2=Stars&Galaxies | 3=Chemicals | 4=Solar System | 5=First Life | 6=TI | 7=Agrarian | 8=Science
Life on Earth: The 5th threshold is life on Earth.