Potentially biogenic carbon preserved in a 4.1 billion-year-old zircon
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- Elizabeth A. Bell
- Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA 90095;
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- Patrick Boehnke
- Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA 90095;
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- T. Mark Harrison
- Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA 90095;
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- Wendy L. Mao
- School of Earth, Energy, and Environmental Sciences, Stanford University, Stanford, CA 94305
説明
<jats:title>Significance</jats:title> <jats:p> Evidence for carbon cycling or biologic activity can be derived from carbon isotopes, because a high <jats:sup>12</jats:sup> C/ <jats:sup>13</jats:sup> C ratio is characteristic of biogenic carbon due to the large isotopic fractionation associated with enzymatic carbon fixation. The earliest materials measured for carbon isotopes at 3.8 Ga are isotopically light, and thus potentially biogenic. Because Earth’s known rock record extends only to ∼4 Ga, earlier periods of history are accessible only through mineral grains deposited in later sediments. We report <jats:sup>12</jats:sup> C/ <jats:sup>13</jats:sup> C of graphite preserved in 4.1-Ga zircon. Its complete encasement in crack-free, undisturbed zircon demonstrates that it is not contamination from more recent geologic processes. Its <jats:sup>12</jats:sup> C-rich isotopic signature may be evidence for the origin of life on Earth by 4.1 Ga. </jats:p>
収録刊行物
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- Proceedings of the National Academy of Sciences
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Proceedings of the National Academy of Sciences 112 (47), 14518-14521, 2015-10-19
Proceedings of the National Academy of Sciences