Oxygen requirements of the earliest animals

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 111; no. 11; pp. 4168 - 4172
• Main Authors: Mills, Daniel B., Ward, Lewis M., Jones, CarriAyne, Sweeten, Brittany, Forth, Michael, Treusch, Alexander H., Canfield, Donald E.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 18.03.2014; National Acad Sciences
• Series: From the Cover
• Subjects: Adaptation, Biological - physiology; Animals; Anoxia; Atmosphere; Atmosphere - chemistry; Atmospherics; Base Sequence; Biological Evolution; Biological Sciences; Denmark; Earth; Fossils; Geochemistry; Kinetics; Microbiota - genetics; Molecular Sequence Data; Morphology; Oceans; Oxygen; Oxygen - analysis; Oxygen Consumption - physiology; Oxygen demand; Oxygen requirement; Oxygenation; Physical Sciences; Polymorphism, Restriction Fragment Length; Porifera - microbiology; Porifera - physiology; Respiration; RNA, Ribosomal, 16S - genetics; Sea water; Sequence Analysis, DNA; Sponges; Tissue oxygenation; Denmark; hypoxia; Metazoa
• ISSN: 0027-8424; 1091-6490; 1091-6490
• DOI: 10.1073/pnas.1400547111

A rise in the oxygen content of the atmosphere and oceans is one of the most popular explanations for the relatively late and abrupt appearance of animal life on Earth. In this scenario, Earth's surface environment failed to meet the high oxygen requirements of animals up until the middle to late Neoproterozoic Era (850—542 million years ago), when oxygen concentrations sufficiently rose to permit the existence of animal life for the first time. Although mulitple lines of geochemical evidence support an oxygenation of the Ediacaran oceans (635—542 million years ago), roughly corresponding with the first appearance of metazoans in the fossil record, the oxygen requirements of basal animals remain unclear. Here we show that modern demosponges, serving as analogs for early animals, can survive under low-oxygen conditions of 0.5—4.0% present atmospheric levels. Because the last common ancestor of metazoans likely exhibited a physiology and morphology similar to that of a modern sponge, its oxygen demands may have been met well before the enhanced oxygenation of the Ediacaran Period. Therefore, the origin of animals may not have been triggered by a contemporaneous rise in the oxygen content of the atmosphere and oceans. Instead, other ecological and developmental processes are needed to adequately explain the origin and earliest evolution of animal life on Earth.