Helium and Argon Isotopic Studies of Fossil Material and the Theoretical Evolution of He and Ar in Earth’s Atmosphere through Time
- 1 Department of Earth and Space Science, Graduate School of Science, Osaka University, Toyonaka, Japan
- 2 Department of Earth and Space Science, Graduate School of Science, Osaka University, Toyonaka, Japan
Abstract
We analyzed the elemental concentrations and the isotopic compositions of helium and argon in Cambrian to Jurrassic aged Gastropod, Ammonite and Trilobite fossils in order to examine variation in these gases through time. Fossil samples yielded He and Ar isotopic ratios close to the present day atmospheric values, but also indicated some addition of a radiogenic component. We compared the results to theoretical values calculated from a mathematical model of Earth’s atmosphere assuming mantle degassing. Results from our mathmatical models showed that the 40Ar/36Ar ratio of Earth’s atmosphere increased rapidly after the formation of the Earth, but has been almost identical to the present day value for the last 1 Ga. For atmospheric helium, model results were consistent with present day atmospheric values, assuming complete helium degassing from the continental crust into the atmosphere. The model suggests that the atmospheric 3He/4He ratio has remained relatively constant for the last 0.1 Ga. Given the similarity between present day and ancient He and Ar isotopic ratios, we conclude that the corresponding ratios measured in ancient fossil material may partially reflect composition of the ancient atmosphere and are not necessarily due to contamination by the present day atmosphere.
- H. Brown, “Rare Gases and the Formation of the Earth’s Atmosphere,” In: C. P. Kuiper, Ed., The Atmospheres of the Earth and Planets, University of Chicago Press, Chicago, 1952, pp. 258-266.
- G. Turner, “The Outgassing History of the Earth’s Atmosphere,” Journal of the Geological Society of London, Vol. 146, No. 1, 1987, pp. 147-154.doi:10.1144/gsjgs.146.1.0147
- K, Kamijo, K. Hashizume and J. Matsuda, “Noble Gas Constraints on the Evolution of the Atmosphere-Mantle System,” Geochimica et Cosmochimica Acta, Vol. 62, No. 13, 1998, pp. 2311-2321. doi:10.1016/S0016-7037(98)00163-X
- A. Seta, T. Matsumoto and J. Matsuda, “Concurrent Evolution of 3He/4He Ratio in the Earth’s Mantle Reser- voirs for the First 2 Ga,” Earth and Planetary Science Letters, Vol. 188, No. 1-2, 2001, pp. 211-219. doi:10.1016/S0012-821X(01)00307-7
- J. Matsuda and B. Marty, “The 40Ar/36Ar Ratio of the Undepleted Mantle; a Reevaluation,” Geophysical Re- search Letters, Vol. 22, No. 15, 1995, pp. 1937-1940.doi:10.1029/95GL01893
- M. Ozima, “Noble Gas State in the Mantle,” Review of Geophysics, Vol. 32, No. 4, 1994, pp. 405-426. doi:10.1029/94RG01875
- J. Matsuda, T. Maruoka, D. L. Pinti and C. Koeberl, “Noble Gas Study of a Philippinite with an Unusually Large Bubble,” Meteoritics and Planetary Science, Vol. 31, No. 2, 1996, pp. 273-277. doi:10.1111/j.1945-5100.1996.tb02023.x
- J. Matsuda, M. Namba, T. Maruoka, T. Matsumoto and G. Kurat, “Primordial Noble Gases in a Graphite-Metal Inclusion from the Canyon Diablo IAB Meteorite and Their Implications,” Meteoritics and Planetary Science, Vol. 45, No. 3, 2005, pp. 361-372. doi:10.1111/j.1945-5100.2010.01026.x
- J. Matsuda, H. Tsukamoto, C. Miyakawa and S. Amari, “Noble Gas Study of the Saratov L4 Chondrite,” Meteoritics and Planetary Science, Vol. 45, No. 3, 2010, pp. 361-372. doi:10.1111/j.1945-5100.2010.01026.x
- J. Matsuda, T. Matsumoto, H, Sumino, K. Nagao, J. Ya- mamoto, Y. Miura, I. Kaneoka, N. Takahata and Y. Sano, “The 3He/4He Ratio of the New Internal He Standard of Japan (HESJ),” Geochemical Journal, Vol. 36, No. 2, 2002, pp. 191-195. doi:10.2343/geochemj.36.191
- S. R. Taylor, “Solar System Evolution. A New Perspective,” 2nd Edition, Cambridge University Press, Cam- bridge, 2001. doi:10.1017/S1360641701342788
- K. P. Jochum, A. W. Hofmann, E. Ito, H. M. Seufert and W. M. White, “K, U and Th in Mid-Ocean Ridge Basalt Glasses and Heat Production, K, U and K/Rb in the Mantle,” Nature, Vol. 306, 1983, pp. 431-436. doi:10.1038/306431a0