Physiological Adaptation in the Neoproterozoic to Early Cambrian to Dynamic Oxygen Fluctuation Challenges Enabled Respiratory Evolution. Oct 2022 Jorma Jyrkkanen

Christopher Clifford 33m · Dynamic Oxygen Levels May Have Accelerated Animal Evolution: "The question scientists have tried to answer is - was there anything extraordinary about the changes to oxygen levels in the Neoproterozoic Era that may have played a pivotal role in the early evolution of animals – did oxygen levels suddenly rise or was there a gradual increase? Dr Benjamin Mills, who leads the Earth Evolution Modelling Group at Leeds and supervised the project, said: “This periodic change in environmental conditions would have produced evolutionary pressures where some life forms may have become extinct and new ones could emerge.” “When oxygen levels decline, there is severe environmental pressure on some organisms which could drive extinctions. And when the oxygen-rich waters expand, the new space allows the survivors to rise to ecological dominance. “These expanded habitable spaces would have lasted for millions of years, giving plenty of time for ecosystems to develop.” Extreme variability in atmospheric oxygen levels in the late Precambrian Alexander J. Krause https://orcid.org/0000-0002-9771-8101 , Benjamin J. W. Mills https://orcid.org/0000-0002-9141-0931, Andrew S. Merdith https://orcid.org/0000-0002-7564-8149, Timothy M. Lenton https://orcid.org/0000-0002-6725-7498, and Simon W. Poulton https://orcid.org/0000-0001-7621-189X Science Advances 14 Oct 2022 Vol 8, Issue 41 Abstract Mapping the history of atmospheric O2 during the late Precambrian is vital for evaluating potential links to animal evolution. Ancient O2 levels are often inferred from geochemical analyses of marine sediments, leading to the assumption that the Earth experienced a stepwise increase in atmospheric O2 during the Neoproterozoic. However, the nature of this hypothesized oxygenation event remains unknown, with suggestions of a more dynamic O2 history in the oceans and major uncertainty over any direct connection between the marine realm and atmospheric O2. Here, we present a continuous quantitative reconstruction of atmospheric O2 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 O2 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 O2 during the Neoproterozoic, and the first animals evolved against a backdrop of extreme O2 variability. Mechanisms of Adaptation Jorma Jyrkkanen Blood stem cells today in mammals have the ability to produce more when challenged by oxygen deficit. Secondary polycythemia most often develops as a response to chronic hypoxemia, which triggers increased production of erythropoietin by the kidneys. This kind of condition may have early antecedents in the Neoproterozoic facilitating adaptation to hypoxia challenge and enabling higher respiratory processes to evolve. Looking for evidence of this capability in more primitive phyla might yield important clues to what exactly happened to improve respiratory adaptation. I suspect mitochondria also improved during this time. Oxygen is central to aerobic respiration—it is the terminal electron acceptor of the mitochondrial electron transport chain (ETC), which transfers electrons from high energy metabolites through a series of carriers to drive ATP generation from ADP. The ability to increase mitochondria in hypoxia challenge may have also facilitated Neoproterozoic respiratory adaptation. These oxygen fluctuations would have created ideal situations for aerobic glycolysis, anaerobic glycolysis, and pyruvate fed xidative phosphorylation metabolisms at various times not to mention ideal situations for alternate metabolisms like methane and CO2 drives. Cancer cells today operate optimally on glycolysis suggesting they may have originated in this dynamic gas fluctuation era.