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Abiogenesis
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Precambrian stromatolites in the Siyeh Formation, Glacier National Park. In 2002, a paper in the scientific journal Nature suggested that these 3.5 Ga (billion years old) geological formations contain fossilized cyanobacteria microbes. This suggests they are evidence of one of the earliest known life forms on Earth.
Abiogenesis (/?e?ba?.?'d??n?s?s/ AY-by-oh-JEN-?-siss) or biopoiesis is the natural process by which life arose from non-living matter such as simple organic compounds. The earliest life on Earth existed at least 3.5 billion years ago, during the Eoarchean Era when sufficient crust had solidified following the molten Hadean Eon. On November 8, 2013, scientists reported the discovery of what might have been the earliest actual signs of life on Earth by that time - the complete fossils of a microbial mat (associated with sandstone in western Australia) estimated to be 3.48 billion years old. Later the date was moved further back by approximately 300 million years when some graphite in the 3.7-billion-year-old metasedimentary rocks in Greenland had been identified as biogenic.Scientific hypotheses about the origins of life can be divided into a number of categories. Many approaches investigate how self-replicating molecules or their components came into existence. On the assumption that life originated spontaneously on Earth, the Miller–Urey experiment and similar experiments demonstrated that most amino acids, often called "the building blocks of life", can be racemically synthesized in conditions intended to be similar to those of the early Earth. Several mechanisms have been investigated, including lightning and radiation. Other approaches ("metabolism first" hypotheses) focus on understanding how catalysis in chemical systems in the early Earth might have provided the precursor molecules necessary for self-replication.
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