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Carbon Isotope Variations and a Bold Hypothesis for Life

Carbon Isotope Variations and a Bold Hypothesis for Life [Pg.95]

Carbon has two stable isotopes, C and C. Natural diamond has 6 C-values between -3 and -5. Diamonds have been formed from carbon in the mantle with an isotopic composition that can be supposed to be in accordance with what existed for the newly created planet earth. The isotopic composition for carbon in meteorites also corresponds to a 6 C-value of -5%o. Inorganic carbonate sediments have the value 0 while organic sediments have the value -25%o. To give a total mean value of-5 the latter must constitute 20% of all sedimentary carbon. Modem estimates [4.9] assert that this value has been constant in almost 4 billion years. That implies that living organisms have been active since very early in the history of our planet [Pg.95]




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