Rise to modern levels of ocean oxygenation coincided with the Cambrian radiation of animals.

Xi Chen,Hong-Fei Ling,Lawrence M Och,Shao-Yong Jiang,Graham A Shields-Zhou,Simon W Poulton,Corey Archer,Da Li,Derek Vance,Lorenzo Cremonese,Maoyan Zhu

doi:10.1038/ncomms8142

Abstract

The early diversification of animals (∼630 Ma), and their development into both motile and macroscopic forms (∼575–565 Ma), has been linked to stepwise increases in the oxygenation of Earth's surface environment. However, establishing such a linkage between oxygen and evolution for the later Cambrian ‘explosion' (540–520 Ma) of new, energy-sapping body plans and behaviours has proved more elusive. Here we present new molybdenum isotope data, which demonstrate that the areal extent of oxygenated bottom waters increased in step with the early Cambrian bioradiation of animals and eukaryotic phytoplankton. Modern-like oxygen levels characterized the ocean at ∼521 Ma for the first time in Earth history. This marks the first establishment of a key environmental factor in modern-like ecosystems, where animals benefit from, and also contribute to, the ‘homeostasis' of marine redox conditions.

Highlights

The early diversification of animals (B630 Ma), and their development into both motile and macroscopic forms (B575–565 Ma), has been linked to stepwise increases in the oxygenation of Earth’s surface environment
We find that the tempo of ocean oxygenation, as reconstructed by the Mo isotope and concentration profiles, was in step with the early Cambrian bioradiation
Late Neoproterozoic to Cambrian successions are well developed in South China

Summary

Introduction

The early diversification of animals (B630 Ma), and their development into both motile and macroscopic forms (B575–565 Ma), has been linked to stepwise increases in the oxygenation of Earth’s surface environment. Establishing such a linkage between oxygen and evolution for the later Cambrian ‘explosion’ (540–520 Ma) of new, energysapping body plans and behaviours has proved more elusive. Proterozoic (B2,400–2,100 Ma), atmospheric PO2 stayed within B0.01 and B10% of the present atmospheric level during the mid-Proterozoic (B2,100–800 Ma (refs 6,7)) It was only after the termination of the Cryogenian glaciations (B635 Ma) that oxygen levels in Earth’s surface environment began to increase significantly again[8,9]. Global marine redox conditions can be inferred from the sedimentary Mo record because of its redox-sensitive deposition and isotope fractionation masecthheanciosmnsse9r,2v9a–t3iv2.eInoxtyhaenmioondemrnoloyxbidcaotepeÀnMooceOa24nÀs,ÁMaot is present relatively high concentrations

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