Abiogenesis
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Abiogenesis (pronounced /ˌeɪbaɪ.ɵˈdʒɛnɨsɪs/ AY-by-oh-JEN-ə-siss) or biopoiesis is the study of how biological life could arise from inorganic matter through natural processes. In particular, the term usually refers to the processes by which life on Earth may have arisen. Most amino acids, often called "the building blocks of life", can form via natural chemical reactions unrelated to life, as demonstrated in the Miller–Urey experiment and similar experiments that involved simulating some of the hypothetical conditions of the early Earth in a laboratory. Other equally fundamental biochemicals, such as nucleotides and saccharides can arise in similar ways. In all living things, these biochemicals are organized into more complex molecules, including macromolecules, such as proteins, polysaccharides, and nucleic acids. These three molecules are essential for all life functions and make up all living organisms. The construction of these macromolecules is mediated by nucleic acids and enzymes, that are themselves synthesized through biochemical pathways catalysed largely by proteins. Which of these various classes of organic molecules first arose, and how they formed the first life, is a major topic in the discipline of abiogenesis. In any theory of abiogenesis, two aspects of life must be accounted for: replication and metabolism. The question of which came first gave rise to different types of theories. In the beginning, metabolism-first theories (Oparin coacervate) were proposed, and only later thinking gave rise to the modern, replication-first approach. The sequence of chemical events that led to the first nucleic acids is not known. Several hypotheses about early life have been proposed, most notably the iron-sulfur world theory (metabolism without genetics) and the RNA world hypothesis (RNA life-forms). The first living things on Earth are thought to have been single cell prokaryotes (which lack a cell nucleus), perhaps evolved from protobionts (organic molecules surrounded by a membrane-like structure). The oldest ancient fossil microbe-like objects are dated to be 3.5 Ga (billion years old), approximately one billion years after the formation of the Earth itself, with reliable fossil evidence of the first life found in rocks 3.4 Gyr old. By 2.4 Ga, the ratio of stable isotopes of carbon, iron and sulfur shows the action of living things on inorganic minerals and sediments and molecular biomarkers indicate photosynthesis, demonstrating that life on Earth was widespread by this time. From Wikipedia under the
GNU Free Documentation License Nounabiogenesis (uncountable)
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GNU Free Documentation License Matching Results for Abiogenesis:ScienceThomas Henry Huxley, Presidential Address at the British Association (1870); " Biogenesis and Abiogenesis ", Collected Essays, vol. 8, p. ... Thomas Henry Huxley Presidential Address at the British Association, "Biogenesi s and abiogenesis " ( 1870); later published in Collected Essays, Vol. 8, p. 229 ... From Wikiquote under the
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