Author:
Zhang Shuichang,Wang Xiaomei,Wang Huajian,Bjerrum Christian J.,Hammarlund Emma U.,Costa M. Mafalda,Connelly James N.,Zhang Baomin,Su Jin,Canfield Donald E.
Abstract
The Mesoproterozoic Eon [1,600–1,000 million years ago (Ma)] is emerging as a key interval in Earth history, with a unique geochemical history that might have influenced the course of biological evolution on Earth. Indeed, although this time interval is rather poorly understood, recent chromium isotope results suggest that atmospheric oxygen levels were <0.1% of present levels, sufficiently low to have inhibited the evolution of animal life. In contrast, using a different approach, we explore the distribution and enrichments of redox-sensitive trace metals in the 1,400 Ma sediments of Unit 3 of the Xiamaling Formation, North China Block. Patterns of trace metal enrichments reveal oxygenated bottom waters during deposition of the sediments, and biomarker results demonstrate the presence of green sulfur bacteria in the water column. Thus, we document an ancient oxygen minimum zone. We develop a simple, yet comprehensive, model of marine carbon−oxygen cycle dynamics to show that our geochemical results are consistent with atmospheric oxygen levels >4% of present-day levels. Therefore, in contrast to previous suggestions, we show that there was sufficient oxygen to fuel animal respiration long before the evolution of animals themselves.
Funder
EC | European Research Council
Danish National Research Foundation
Ministry of Science, Innovation and Higher Education | Danish Agency for Science, Technology and Innovation
National Natural Science Foundation of China
China National Petroleum Corporation
Publisher
Proceedings of the National Academy of Sciences
Cited by
260 articles.
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