Sufficient oxygen for animal respiration 1,400 million years ago

Summary, in English

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.

• Author: Shuichang Zhang; Xiaomei Wang; Huajian Wang; Christian J Bjerrum; Emma U Hammarlund; M Mafalda Costa; James N Connelly; Baomin Zhang; Jin Su; Donald E Canfield
• Publishing year: 2016-02-16
• Language: English
• Pages: 6-1731
• Publication/Series: Proceedings of the National Academy of Sciences of the United States of America
• Volume: 113
• Issue: 7
• Links: http://dx.doi.org/10.1073/pnas.1523449113
• Document type: Journal article
• Publisher: National Academy of Sciences
• Keywords: Animals; Atmosphere; Biological Evolution; Oxygen; Respiration; Water; Journal Article; Research Support, Non-U.S. Gov't
• Status: Published
• ISBN/ISSN/Other: ISSN: 1091-6490