Petrographic carbon in ancient sediments constrains Proterozoic Era atmospheric oxygen levels

Abstract

Oxygen concentration defines the chemical structure of Earth's ecosystems while it also fuels the metabolism of aerobic organisms. As different aerobes have different oxygen requirements, the evolution of oxygen levels through time has likely impacted both environmental chemistry and the history of life. Understanding the relationship between atmospheric oxygen levels, the chemical environment, and life, however, is hampered by uncertainties in the history of oxygen levels. We report over 5,700 Raman analyses of organic matter from nine geological formations spanning in time from 742 to 1,729 Ma. We find that organic matter was effectively oxidized during weathering and little was recycled into marine sediments. Indeed, during this time interval, organic matter was as efficiently oxidized during weathering as it is now. From these observations, we constrain minimum atmospheric oxygen levels to between 2 to 24% of present levels from the late Paleoproterozoic Era into the Neoproterozoic Era. Indeed, our results reveal that eukaryote evolution, including early animal evolution, was not likely hindered by oxygen through this time interval. Our results also show that due to efficient organic recycling during weathering, carbon cycle dynamics can be assessed directly from the sediment carbon record.

Strong evidence for a weakly oxygenated ocean–atmosphere system during the Proterozoic

“… 3 ) remains debated. Specifically, an O 2 control on eukaryote complexity has recently been challenged on the grounds that the O 2 requirements of primitive animals were exceeded well before their evolution ( 7 – 9 ). Much of the debate stems from uncertainties associated with the assumptions used in various paleoredox approaches to translate geochemical data from sedimentary rocks into O 2 estimates ( 5 , 9 , 10 ), leading to estimates that span over an order of magnitude (e.g., refs.…”

“…Much of the debate stems from uncertainties associated with the assumptions used in various paleoredox approaches to translate geochemical data from sedimentary rocks into O 2 estimates ( 5 , 9 , 10 ), leading to estimates that span over an order of magnitude (e.g., refs. 4 , 5 , 7 , 8 , 43 ).…”

“…However, the atmospheric O 2 levels ( p O 2 ) of the ocean–atmosphere system during Earth’s intervening history (i.e., the middle Proterozoic) are highly debated: Despite suggestions that p O 2 remained relatively low during this time ( 4 – 6 ), recent work has argued that the O 2 demands of complex eukaryotes may have been exceeded well before their evolution (e.g., refs. 7 – 10 ). Therefore, the nature of the relationships between surface oxygenation and the evolutionary ecology of early complex life remain contentious ( 8 , 11 ).…”

“… 7 – 10 ). Therefore, the nature of the relationships between surface oxygenation and the evolutionary ecology of early complex life remain contentious ( 8 , 11 ). Because surface redox conditions can affect the geochemistry of contemporaneous sediments, several geochemical indices from ancient sedimentary rocks have been employed as proxies for mid-Proterozoic atmospheric p O 2 , predominantly the abundance or isotopic composition of redox-sensitive trace metals in marine carbonate rocks or shales (e.g., refs.…”

Multi-Element Imaging of a 1.4 Ga Authigenic Siderite Crystal

“…Therefore, the most possible source should be biologically recycled continental Fe, which has been suggested as a major component in the 2.5 Ga Dales Gorge member IF [45]. Considering the still low oxidation levels in Mesoproterozoic atmosphere and ocean [46,47], the iron cycle in the ocean might be comparable to that of the terminal Archaean [36]. No matter which reason takes over, a ferruginous-dominated ocean during the Xiamaling Formation has already been confirmed [6,33,34,36,42,48].…”