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Natural abundance
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<h2 id="deviations-from-natural-abundance">Deviations from natural abundance</h2> <p>It is now known from study of the Sun and primitive meteorites that the <a href="/facts/Solar_System/QIcLSazQ">Solar System</a> was initially almost homogeneous in isotopic composition. Deviations from the (evolving) galactic average, locally sampled around the time that the Sun's nuclear burning began, can generally be accounted for by mass fractionation (see the article on <a href="/facts/Mass-independent_fractionation/WWlxREGy">mass-independent fractionation</a>) plus a limited number of nuclear decay and transmutation processes.<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a> There is also evidence for injection of short-lived (now-extinct) isotopes from a nearby supernova explosion that may have triggered solar nebula collapse.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> Hence deviations from natural abundance on Earth are often measured in parts per thousand (<a href="/facts/Per_mille/3xNDvE9l">per mille</a> or ‰) because they are less than one percent (%). </p><p>An exception to this lies with the <a href="/facts/Presolar_grains/Sb89tnPP">presolar grains</a> found in primitive meteorites. These small grains condensed in the outflows of evolved ("dying") stars and escaped the mixing and homogenization processes in the interstellar medium and the solar accretion disk (also known as the solar nebula or protoplanetary disk).<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> As stellar condensates ("stardust"), these grains carry the isotopic signatures of specific nucleosynthesis processes in which their elements were made.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> In these materials, deviations from "natural abundance" are sometimes measured in factors of 100.<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a> </p> <h2 id="natural-isotope-abundance-of-some-elements">Natural isotope abundance of some elements</h2> <p>The next table gives the <a href="/facts/Earth/HLLmDfj0">terrestrial</a> isotope distributions for some elements. Some elements, such as <a href="/facts/Phosphorus/27xCeIqs">phosphorus</a> and <a href="/facts/Fluorine/YUV0Fb8m">fluorine</a>, only exist as a single isotope, with a natural abundance of 100%. </p> Natural isotope abundance of some elements on Earth<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a><table><tbody><tr><th><i>Isotope</i></th><th>% nat. abundance</th><th>atomic mass</th></tr><tr><td>1H</td><td>99.985</td><td>1.007825</td></tr><tr><td><a href="/facts/Deuterium/Bv4wfCkw">2H</a></td><td>0.015</td><td>2.0140</td></tr><tr><td><a href="/facts/Carbon-12/nJYECzEr">12C</a></td><td>98.89</td><td>12 (formerly by definition)</td></tr><tr><td><a href="/facts/Carbon-13/Iho4LUtW">13C</a></td><td>1.11</td><td>13.00335</td></tr><tr><td>14N</td><td>99.64</td><td>14.00307</td></tr><tr><td>15N</td><td>0.36</td><td>15.00011</td></tr><tr><td><a href="/facts/Oxygen-16/osheCBxR">16O</a></td><td>99.76</td><td>15.99491</td></tr><tr><td><a href="/facts/Oxygen-17/LBY5W95R">17O</a></td><td>0.04</td><td>16.99913</td></tr><tr><td><a href="/facts/Oxygen-18/fK0gerlA">18O</a></td><td>0.2</td><td>17.99916</td></tr><tr><td>28Si</td><td>92.23</td><td>27.97693</td></tr><tr><td>29Si</td><td>4.67</td><td>28.97649</td></tr><tr><td>30Si</td><td>3.10</td><td>29.97376</td></tr><tr><td>32S</td><td>95.0</td><td>31.97207</td></tr><tr><td>33S</td><td>0.76</td><td>32.97146</td></tr><tr><td>34S</td><td>4.22</td><td>33.96786</td></tr><tr><td>35Cl</td><td>75.77</td><td>34.96885</td></tr><tr><td>37Cl</td><td>24.23</td><td>36.96590</td></tr><tr><td>79Br</td><td>50.69</td><td>78.9183</td></tr><tr><td>81Br</td><td>49.31</td><td>80.9163</td></tr></tbody></table> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Abundance_of_the_chemical_elements/CE9WehBl">Abundance of the chemical elements</a></li> <li><a href="/facts/Decay_product/hT0obfLv">Decay product</a></li> <li><a href="/facts/Isotope/KD9B1y6o">Isotope</a></li> <li><a href="/facts/Presolar_grains/Sb89tnPP">Presolar grains</a></li> <li><a href="/facts/Radionuclide/5WpCfbdq">Radionuclide</a></li></ul> <h2 id="external-links">External links</h2> <ul><li><a href="https://web.archive.org/web/20150707182753/http://ie.lbl.gov/education/isotopes.htm">Berkeley Isotopes Project Interactive Table</a> (archived 2015)</li> <li><a href="https://www.sisweb.com/referenc/source/exactmas.htm">Exact Masses of the Elements and Isotopic Abundances</a>, Scientific Instrument Services</li> <li><a href="https://web.archive.org/web/20110826012824/http://research.smilems.com/molecule-tk/">Tools to compute low- and high-precision isotopic distribution</a> (archived 2011)</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>"Uranium Isotopes". GlobalSecurity.org. Retrieved 14 March 2012. <a href="https://www.globalsecurity.org/wmd/intro/u-isotopes.htm" target="_blank">https://www.globalsecurity.org/wmd/intro/u-isotopes.htm</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Clayton, Robert N. (1978). "Isotopic anomalies in the early solar system". Annual Review of Nuclear and Particle Science. 28: 501–522. Bibcode:1978ARNPS..28..501C. doi:10.1146/annurev.ns.28.120178.002441. <a href="/wiki/Annual_Review_of_Nuclear_and_Particle_Science" target="_blank">/wiki/Annual_Review_of_Nuclear_and_Particle_Science</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Zinner, Ernst (2003). "An isotopic view of the early solar system". Science. 300 (5617): 265–267. doi:10.1126/science.1080300. PMID 12690180. S2CID 118638578. <a href="https://www.science.org/doi/abs/10.1126/science.1080300" target="_blank">https://www.science.org/doi/abs/10.1126/science.1080300</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Anders, Edward; Zinner, Ernst (1993). "Interstellar Grains in Primitive Meteorites: Diamond, Silicon Carbide, and Graphite". Meteoritics. 28 (4): 490–514. Bibcode:1993Metic..28..490A. doi:10.1111/j.1945-5100.1993.tb00274.x. <a href="https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1945-5100.1993.tb00274.x" target="_blank">https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1945-5100.1993.tb00274.x</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Zinner, Ernst (1998). "Stellar nucleosynthesis and the isotopic composition of presolar grains from primitive meteorites". Annual Review of Earth and Planetary Sciences. 26: 147–188. Bibcode:1998AREPS..26..147Z. doi:10.1146/annurev.earth.26.1.147. <a href="/wiki/Annual_Review_of_Earth_and_Planetary_Sciences" target="_blank">/wiki/Annual_Review_of_Earth_and_Planetary_Sciences</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Anders, Edward; Zinner, Ernst (1993). "Interstellar Grains in Primitive Meteorites: Diamond, Silicon Carbide, and Graphite". Meteoritics. 28 (4): 490–514. Bibcode:1993Metic..28..490A. doi:10.1111/j.1945-5100.1993.tb00274.x. <a href="https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1945-5100.1993.tb00274.x" target="_blank">https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1945-5100.1993.tb00274.x</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>Lide, D. R., ed. (2002). CRC Handbook of Chemistry and Physics (83rd ed.). Boca Raton, Florida: CRC Press. ISBN 0-8493-0483-0. <a href="0-8493-0483-0" target="_blank">0-8493-0483-0</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> </ol>