Pulse of atmospheric oxygen during the late Cambrian

Abstract

A rise in atmospheric O 2 has been linked to the Cambrian explosion of life. For the plankton and animal radiation that began some 40 million yr later and continued through much of the Ordovician (Great Ordovician Biodiversification Event), the search for an environmental trigger(s) has remained elusive. Here we present a carbon and sulfur isotope mass balance model for the latest Cambrian time interval spanning the globally recognized Steptoean Positive Carbon Isotope Excursion (SPICE) that indicates a major increase in atmospheric O 2 . We estimate that this organic carbon and pyrite burial event added approximately 19 × 10 18 moles of O 2 to the atmosphere (i.e., equal to change from an initial starting point for O 2 between 10–18% to a peak of 20–28% O 2 ) beginning at approximately 500 million years. We further report on new paired carbon isotope results from carbonate and organic matter through the SPICE in North America, Australia, and China that reveal an approximately 2‰ increase in biological fractionation, also consistent with a major increase in atmospheric O 2 . The SPICE is followed by an increase in plankton diversity that may relate to changes in macro- and micronutrient abundances in increasingly oxic marine environments, representing a critical initial step in the trophic chain. Ecologically diverse plankton groups could provide new food sources for an animal biota expanding into progressively more ventilated marine habitats during the Ordovician, ultimately establishing complex ecosystems that are a hallmark of the Great Ordovician Biodiversification Event.

Diversity partitioning during the Cambrian radiation

“…For example, prolonged tropical warming has been suggested to explain the scarcity of metazoan reefs in the later Cambrian (35) and would also fit the gamma diversity trajectories given that cooling is thought to have facilitated the subsequent Ordovician radiation (36). Alternatively, a late Cambrian rise in oxygen levels has been proposed to explain the onset of the Ordovician radiation (37). By inference, oxygen limitation may have hindered further diversification after the early Cambrian.…”

Oxygen-isotope trends and seawater temperature changes across the Late Cambrian Steptoean positive carbon-isotope excursion (SPICE event)

“…The SPICE is associated with (1) a positive δ 34 S excursion recorded within pyrite and carbonate-associated sulfate (Gill et al, 2011), (2) a decrease in Mo isotopes and concentrations (Gill et al, 2011), (3) a long-term sea-level fall (Saltzman et al, 2004), and (4) an increase in δ 13 C of C org (Saltzman et al, 2011). These combined data led Hurtgen et al (2009) andGill et al (2011) to suggest that the SPICE represents widespread ocean anoxia and associated enhanced burial of C org and pyrite.…”

Oxidative stress in Fanconi anaemia: from cells and molecules towards prospects in clinical management

“…On a merely logical basis, one might wonder about nature ' s aim at building up an evolutionary conserved gene set, targeted at defending genome stability against other threats rather than humanmade ' crosslinkers ' . The obvious answer may be that postCambrian aerobic biota are all faced with the generalized damages exerted by atmospheric oxygen, the second most reactive non-metallic element after fl uorine (Saltzman et al , 2011 ). Thus, one might reason that the roles of FANC proteins in DNA repair should be at least in part also related to (a) coping with the primogenial oxygen toxicity and (b) disposing of excess endogenous and/or of exogenous molecules by means of oxygen-based redox pathways, as in the case of the P450 enzyme family.…”