From consideration of the volumes of halite and associated salts deposited since the Permian, one must infer that either seawater at the close of the Paleozoic was hypersaline compared with seas of today (35^pmil salinity); or, although 6 million cu km or more of salt has been precipitated from the world ocean in highly varying amounts at irregular intervals since the Permian, an equal volume of salt has gone into solution. Data from analysis of sedimentary sulfur-isotope ratios strongly support the former inference. Concordant, but more speculative, support also is available from aridity indices.

A condition of hypersalinity in the oceans during the Permian Period would explain the known patterns of Permian extinctions. Evidence suggests that those marine taxa (e.g., echinoderms, fusulines, coelenterates) with the lowest tolerance for salinity variability were the group within the entire Permian biota that suffered the greatest proportion of extinctions at the close of the Paleozoic. Such an explanation is more consistent with a uniformitarian earth than causes sought in cosmic radiation variability or pulses, which should have affected terrestrial organisms more strongly than marine taxa.

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