For reasons that remain unclear, the initial appearance of large, morphologically complex life on Earth seems to have taken place in deep-marine environments. We provide new perspective on this topic by applying for the first time the vanadium (V) isotope paleoredox-proxy. We use shales in two different sections that preserve Doushantuo Member IV (South China) to reconstruct a global seawater V isotope composition (delta V-51=similar to-0.23 +/- 0.06 parts per thousand) during the late-Ediacaran (similar to 567 to >= 560 million years ago) that is much lighter than today. A mass-balance model informed by this composition is only reconciled by a global ocean in which hydrogen sulfide-rich ('euxinic') conditions were commonly present on continental shelves. Higher surface temperatures are a known driver of widespread euxinia in Earth's past, and if this was also the case during the late-Ediacaran, then relegation of large complex life to deep-marine settings at this time was probably driven to some extent by the persistently cooler and sulfide-poor conditions offered by this refuge. (C) 2021 Elsevier B.V. All rights reserved.

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