image: Looking east-northeast across the east limb of the Kerdous Inlier in Morocco, nearly two kilometers of layered carbonate rock span the beginning of the Cambrian explosion, from the Ediacaran-Cambrian boundary in the nearest foreground, to the first appearance of trilobites on the near horizon. The snow-capped High Atlas Mountains are the farthest horizon. view more
Credit: Image courtesy of Adam C. Maloof.
Major fluctuations in atmospheric and oceanic oxygen during the Cambrian explosion may have been driven partly by the appearance of animals living at the seafloor, according to a study. In a relatively short period, approximately 540-520 million years ago, all major animal groups appeared in the fossil record, including those that live above anoxic seafloor sediment. Ocean oxygenation fluctuated dramatically during this Cambrian explosion. Tais W. Dahl and colleagues sought to illuminate the interplay of the fluctuations and the radiation of animal life. To determine the timing and interplay of oceanic and atmospheric oxygen, the authors analyzed 187 ancient seafloor samples from China, Siberia, and Morocco and compared the results with animal appearances in the fossil record. Uranium isotope composition served as an indicator of oceanic oxygen, whereas measurements of other isotopes in the same sediment served to approximate oxygen concentration at Earth's surface. The results indicate a highly variable system with 2 significant anoxic periods in the ocean following declining atmospheric oxygen concentrations. According to the authors, the findings suggest that the first atmospheric drop in oxygen concentrations was due to benthic animals burrowing in the seafloor, thus limiting phosphorus availability to oxygen-producing phytoplankton.
Article #19-01178: "Atmosphere-ocean oxygen and productivity dynamics during early animal radiations," by Tais W. Dahl et al.
MEDIA CONTACT: Tais W. Dahl, University of Copenhagen, DENMARK; e-mail: tais.dahl@ign.ku.dk
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Journal
Proceedings of the National Academy of Sciences