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A carbon isotope challenge to the snowball Earth

Abstract : The snowball Earth hypothesis postulates that the planet was entirely covered by ice for millions of years in the Neoproterozoic era, in a self-enhanced glaciation caused by the high albedo of the ice-covered planet. In a hard-snowball picture, the subsequent rapid unfreezing resulted from an ultra-greenhouse event attributed to the buildup of volcanic carbon dioxide (CO2) during glaciation. High partial pressures of atmospheric CO2 (; from 20,000 to 90,000p.p.m.v.) in the aftermath of the Marinoan glaciation (~635Myr ago) have been inferred from both boron and triple oxygen isotopes. These values are 50 to 225 times higher than present-day levels. Here, we re-evaluate these estimates using paired carbon isotopic data for carbonate layers that cap Neoproterozoic glacial deposits and are considered to record post-glacial sea level rise. The new data reported here for Brazilian cap carbonates, together with previous ones for time-equivalent units, provide estimates lower than 3,200p.p.m.v.--and possibly as low as the current value of ~400p.p.m.v. Our new constraint, and our re-interpretation of the boron and triple oxygen isotope data, provide a completely different picture of the late Neoproterozoic environment, with low atmospheric concentrations of carbon dioxide and oxygen that are inconsistent with a hard-snowball Earth.
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Submitted on : Friday, March 11, 2022 - 6:05:28 PM
Last modification on : Friday, May 6, 2022 - 2:54:35 PM

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P. Sansjofre, M. Ader, R. I. F. Trindade, M. Elie, J. Lyons, et al.. A carbon isotope challenge to the snowball Earth. Nature, Nature Publishing Group, 2011, 478, pp.93-96. ⟨10.1038/nature10499⟩. ⟨insu-03606441⟩

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