Abiogenesis
<p ><b>Abiogenesis</b> (<small>pronounced </small><a href="http://en.wikipedia.org/wiki/Wikipedia:IPA_for_English" title="Wikipedia:IPA for English" >/ˌeɪbaɪ.ɵˈdʒɛnɨsɪs/</a> <a href="http://en.wikipedia.org/wiki/Wikipedia:Pronunciation_respelling_key" title="Wikipedia:Pronunciation respelling key" ><i><b>ay</b>-by-oh-<b>jen</b>-ə-siss</i></a>) or <b>biopoiesis</b> is the study of how biological <a href="http://en.wikipedia.org/wiki/Life" title="Life" >life</a> could arise from inorganic <a href="http://en.wikipedia.org/wiki/Matter" title="Matter" >matter</a> through natural processes. </p>
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In particular, the term usually refers to the processes by which <a href="http://en.wikipedia.org/wiki/Organism" title="Organism" >life on Earth</a> may have arisen. </p>
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The geologic era in which abiogenesis likely took place was the early <a href="http://en.wikipedia.org/wiki/Eoarchean" title="Eoarchean" >Eoarchean</a> era
(between 4.0 and 3.6, i.e. the time after the <a href="http://en.wikipedia.org/wiki/Hadean" title="Hadean" >Hadean</a> era in which the Earth was essentially molten)
with abiogenesis occurring between 3.9 and 3.5 billion years ago.</p>
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Most <a href="http://en.wikipedia.org/wiki/Amino_acid" title="Amino acid" >amino acids</a>, often called "the building blocks of life", were shown to be synthesized in the <a href="http://en.wikipedia.org/wiki/Miller%E2%80%93Urey_experiment" title="Miller–Urey experiment" >Miller–Urey experiment</a> and similar experiments that involved the simulation some of the hypothetical conditions of the early Earth. Other equally fundamental <a href="http://en.wikipedia.org/wiki/Biochemistry" title="Biochemistry" >biochemicals</a>, such as <a href="http://en.wikipedia.org/wiki/Nucleotide" title="Nucleotide" >nucleotides</a> and <a href="http://en.wikipedia.org/wiki/Carbohydrate" title="Carbohydrate" >saccharides</a> can arise in a similar manner. In all organisms, these biochemicals are organized into more complex molecules, such as <a href="http://en.wikipedia.org/wiki/Protein" title="Protein" >proteins</a>,<a href="http://en.wikipedia.org/wiki/Polysaccharide" title="Polysaccharide" >polysaccharides</a>, and <a href="http://en.wikipedia.org/wiki/Nucleic_acid" title="Nucleic acid" >nucleic acids</a>. These three molecules are essential for all life functions and are common to all presently living organisms. The construction of these macromolecules is mediated by <a href="http://en.wikipedia.org/wiki/Nucleic_acid" title="Nucleic acid" >nucleic acids</a> and <a href="http://en.wikipedia.org/wiki/Enzyme" title="Enzyme" >enzymes</a>, that are themselves synthesized through biochemical pathways catalysed largely by proteins. Which of these classes of <a href="http://en.wikipedia.org/wiki/Organic_molecules" title="Organic molecules" class="mw-redirect" >organic molecules</a> first arose, and how they might have come together to form the first living organisms, has been in the past a major topic of abiogenesis.
The first living things on Earth are thought to have been <a href="http://en.wikipedia.org/wiki/Unicellular" title="Unicellular" class="mw-redirect" >single-cell</a> <a href="http://en.wikipedia.org/wiki/Prokaryote" title="Prokaryote" >prokaryotes</a> (which lack a cell nucleus), perhaps evolved from <a href="http://en.wikipedia.org/wiki/Protobiont" title="Protobiont" >protobionts</a>(organic molecules surrounded by a membrane-like structure).<sup id="cite_ref-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Abiogenesis#cite_note-0" >[1]</a></sup> The oldest ancient fossil microbe-like objects are dated to be 3.5 <a href="http://en.wikipedia.org/wiki/Gigayear" title="Gigayear" class="mw-redirect" >Ga</a> (billion years old), approximately one billion years after the formation of the Earth itself,<sup id="cite_ref-Wilde2001_1-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Abiogenesis#cite_note-Wilde2001-1" >[2]</a></sup><sup id="cite_ref-Schopf2002_2-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Abiogenesis#cite_note-Schopf2002-2" >[3]</a></sup> with reliable fossil evidence of the first life found in rocks 3.4 Gyr old.<sup id="cite_ref-3" class="reference" ><a href="http://en.wikipedia.org/wiki/Abiogenesis#cite_note-3" >[4]</a></sup> By 2.4 Ga, the ratio of stable <a href="http://en.wikipedia.org/wiki/Isotopes" title="Isotopes" class="mw-redirect" >isotopes</a> of <a href="http://en.wikipedia.org/wiki/Carbon" title="Carbon" >carbon</a>, <a href="http://en.wikipedia.org/wiki/Iron" title="Iron" >iron</a> and <a href="http://en.wikipedia.org/wiki/Sulfur" title="Sulfur" >sulfur</a> shows the action of living things on inorganic minerals and sediments<sup id="cite_ref-Hayes2006_4-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Abiogenesis#cite_note-Hayes2006-4" >[5]</a></sup><sup id="cite_ref-Archer2006_5-0" class="reference" ><a href="http://en.wikipedia.org/wiki/Abiogenesis#cite_note-Archer2006-5" >[6]</a></sup> and molecular biomarkers indicate <a href="http://en.wikipedia.org/wiki/Photosynthesis" title="Photosynthesis" >photosynthesis</a>, demonstrating that life on Earth was widespread by this time.<sup id="cite_ref-6" class="reference" ><a href="http://en.wikipedia.org/wiki/Abiogenesis#cite_note-6" >[7]</a></sup><sup id="cite_ref-7" class="reference" ><a href="http://en.wikipedia.org/wiki/Abiogenesis#cite_note-7" >[8]</a></sup>
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<h2 >See also</h2>
<ul >
<li ><a href="http://en.wikipedia.org/wiki/Artificial_cell" title="Artificial cell" >Artificial cell</a></li>
<li ><a href="http://en.wikipedia.org/wiki/Astrochemistry" title="Astrochemistry" >Astrochemistry</a></li>
<li ><a href="http://en.wikipedia.org/wiki/Biological_immortality" title="Biological immortality" >Biological immortality</a></li>
<li ><a href="http://en.wikipedia.org/wiki/Common_descent" title="Common descent" >Common descent</a></li>
<li ><a href="http://en.wikipedia.org/wiki/Entropy_and_life" title="Entropy and life" >Entropy and life</a></li>
<li ><a href="http://en.wikipedia.org/wiki/List_of_independent_discoveries" title="List of independent discoveries" class="mw-redirect" >List of independent discoveries</a></li>
<li ><a href="http://en.wikipedia.org/wiki/Mediocrity_principle" title="Mediocrity principle" >Mediocrity principle</a></li>
<li ><a href="http://en.wikipedia.org/wiki/Mimivirus" title="Mimivirus" >Mimivirus</a></li>
<li ><a href="http://en.wikipedia.org/wiki/Planetary_habitability" title="Planetary habitability" >Planetary habitability</a></li>
<li ><a href="http://en.wikipedia.org/wiki/Rare_Earth_hypothesis" title="Rare Earth hypothesis" >Rare Earth hypothesis</a></li>
<li ><a href="http://en.wikipedia.org/wiki/Shadow_biosphere" title="Shadow biosphere" >Shadow biosphere</a></li>
</ul>
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