Extreme variability in atmospheric oxygen levels in the late Precambrian

Abstract

Mapping the history of atmospheric O 2 during the late Precambrian is vital for evaluating potential links to animal evolution. Ancient O 2 levels are often inferred from geochemical analyses of marine sediments, leading to the assumption that the Earth experienced a stepwise increase in atmospheric O 2 during the Neoproterozoic. However, the nature of this hypothesized oxygenation event remains unknown, with suggestions of a more dynamic O 2 history in the oceans and major uncertainty over any direct connection between the marine realm and atmospheric O 2 . Here, we present a continuous quantitative reconstruction of atmospheric O 2 over the past 1.5 billion years using an isotope mass balance approach that combines bulk geochemistry and tectonic recycling rate calculations. We predict that atmospheric O 2 levels during the Neoproterozoic oscillated between ~1 and ~50% of the present atmospheric level. We conclude that there was no simple unidirectional rise in atmospheric O 2 during the Neoproterozoic, and the first animals evolved against a backdrop of extreme O 2 variability.

Lithium isotopic constraints on the evolution of continental clay mineral factory and marine oxygenation in the earliest Paleozoic Era

“…However, these data indicate that changes in continental clay formation and delivery can potentially serve as important levers on the global oxygen cycle. In sum, the synthesis of our Li isotope data and the results of this numerical modeling exercise indicate that amplified delivery of continental clays to coastal and shallow-marine settings may have facilitated increases in atmospheric and global ocean levels after the early Cambrian ( 14 , 15 , 75 , 82 ). Although early Paleozoic oxygen levels were likely characterized by lower and more variable oxygen levels than those of the modern Earth (Fig.…”

“…The terrestrial OC burial flux was set to zero in these simulations with the assumption of extremely limited terrestrial export productivity before the rise of land plants. Given estimated p O 2 levels of 5 to 40% PAL (present atmospheric level) for the late Neoproterozoic atmosphere ( 82 ), our model results suggest that gradually accelerated continental clay delivery to continental shelves could lead to notable increases in OC burial efficiency. This shift in OC burial efficiency, in turn, could have led to relatively substantial (albeit still low in absolute magnitude, compared to the modern Earth system) increases in atmospheric and marine oxygen levels.…”

“…Although early Paleozoic oxygen levels were likely characterized by lower and more variable oxygen levels than those of the modern Earth (Fig. 3) ( 13 , 14 , 16 , 82 ), increases in continental clay production and delivery may have decreased sedimentary dissolved oxygen consumption, leading to a progressive expansion of oxygenated seawater during the early radiation of animals.…”

Respiration kinetics and allometric scaling in the demosponge Halichondria panicea

“…[102]). It is also likely that they evolved in an environment with signi cantly lower oxygen levels than today, with levels that are uncertain, but with recent estimates suggesting large variability and concentrations ranging from between 1-50% of present levels [103,104]. Given our results, one might expect that large sponges would be part of the geologic record back to their earliest evolution, even in a relatively low oxygen world.…”

Cooling Oceans Did Trigger Ordovician Biodiversification

“…34 shows a very limited change in the thermal tolerance of marine organisms over the last 500 million years. In addition, several lines of evidence suggest that the atmospheric oxygen concentration was, if anything 16,17 , lower than today during the early Paleozoic 35,36 . Due to the increase in organism metabolism (thus dissolved oxygen consumption) with increasing temperatures, a reduced ocean oxygenation would lower the thermal upper limit for marine ectotherms compared to Modern 27 .…”