title: Sufficient oxygen for animal respiration 1,400 million years ago.
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.
authors.affiliation: Key Laboratory of Petroleum Geochemistry, Research Institute of Petroleum Exploration and Development, China National Petroleum Corporation, Beijing 100083, China; sczhang@petrochina.com.cn dec@biology.sdu.dk.
authors.forename: Shuichang
authors.initials: S
authors.lastname: Zhang
authors.affiliation: Key Laboratory of Petroleum Geochemistry, Research Institute of Petroleum Exploration and Development, China National Petroleum Corporation, Beijing 100083, China;
authors.forename: Xiaomei
authors.initials: X
authors.lastname: Wang
authors.affiliation: Key Laboratory of Petroleum Geochemistry, Research Institute of Petroleum Exploration and Development, China National Petroleum Corporation, Beijing 100083, China;
authors.forename: Huajian
authors.initials: H
authors.lastname: Wang
authors.affiliation: Department of Geosciences and Natural Resource Management, Section of Geology, University of Copenhagen, DK-1350 Copenhagen, Denmark; The Nordic Center for Earth Evolution at the Department of Geosciences and Natural Resource Management, Section of Geology, University of Copenhagen, DK-1350 Copenhagen, Denmark;
authors.forename: Christian J
authors.initials: CJ
authors.lastname: Bjerrum
authors.affiliation: Institute of Biology, University of Southern Denmark, DK-5230 Odense, Denmark; The Nordic Center for Earth Evolution at the Institute of Biology, University of Southern Denmark, DK-5230 Odense, Denmark;
authors.forename: Emma U
authors.initials: EU
authors.lastname: Hammarlund
authors.affiliation: Centre for Star and Planet Formation, University of Copenhagen, DK-1350 Copenhagen, Denmark; Natural History Museum of Denmark, University of Copenhagen, DK-1350 Copenhagen, Denmark.
authors.forename: M Mafalda
authors.initials: MM
authors.lastname: Costa
authors.affiliation: Centre for Star and Planet Formation, University of Copenhagen, DK-1350 Copenhagen, Denmark; Natural History Museum of Denmark, University of Copenhagen, DK-1350 Copenhagen, Denmark.
authors.forename: James N
authors.initials: JN
authors.lastname: Connelly
authors.affiliation: Key Laboratory of Petroleum Geochemistry, Research Institute of Petroleum Exploration and Development, China National Petroleum Corporation, Beijing 100083, China;
authors.forename: Baomin
authors.initials: B
authors.lastname: Zhang
authors.affiliation: Key Laboratory of Petroleum Geochemistry, Research Institute of Petroleum Exploration and Development, China National Petroleum Corporation, Beijing 100083, China;
authors.forename: Jin
authors.initials: J
authors.lastname: Su
authors.affiliation: Institute of Biology, University of Southern Denmark, DK-5230 Odense, Denmark; The Nordic Center for Earth Evolution at the Institute of Biology, University of Southern Denmark, DK-5230 Odense, Denmark; sczhang@petrochina.com.cn dec@biology.sdu.dk.
authors.forename: Donald E
authors.initials: DE
authors.lastname: Canfield
mesh_terms: D000818:Animals; D001272:Atmosphere; D005075:Biological Evolution; D010100:Oxygen / Q000032:analysis*; D012119:Respiration; D014867:Water / Q000737:chemistry
chemical_list: D014867:Water; D010100:Oxygen
keywords: Mesoproterozoic; atmosphere; biomarkers; oxygen minimum zone; trace metals