The rapid increase of carbon dioxide concentration in Earth's modern atmosphere is a matter of major concern. But for the atmosphere of roughly two-and-half billion years ago, interest centres on a different gas: free oxygen (O2) spawned by early biological production. The initial increase of O2 in the atmosphere, its delayed build-up in the ocean, its increase to near-modern levels in the sea and air two billion years later, and its cause-and-effect relationship with life are among the most compelling stories in Earth's history.

Ketone bodies , β-hydroxybutyrate (BHB) and acetoacetate support mammalian survival during states of energy deficit by serving as alternative source of ATP1. BHB levels are elevated during starvation, high-intensity exercise or by the low carbohydrate ketogenic diet2. Prolonged caloric restriction or fasting reduces inflammation as immune system adapts to low glucose supply and energy metabolism switches towards mitochondrial fatty acid oxidation, ketogenesis and ketolysis2-6. However, role of ketones bodies in regulation of innate immune response is unknown. We report that BHB, but neither acetoacetate nor structurally-related short chain fatty acids, butyrate and acetate, suppresses activation of the NLRP3 inflammasome in response to several structurally unrelated NLRP3 activators, without impacting NLRC4, AIM2 or non-canonical caspase-11 inflammasome activation. Mechanistically, BHB inhibits NLRP3 inflammasome by preventing K+ efflux and reducing ASC oligomerization and speck formation. The inhibitory effects of BHB on NLRP3 were not dependent on chirality or classical starvation regulated mechanisms like AMPK, reactive oxygen species (ROS), autophagy or glycolytic inhibition. BHB blocked NLRP3 inflammasome without undergoing oxidation in TCA cycle, independently of uncoupling protein-2 (UCP2), Sirt2, receptor Gpr109a and inhibition of NLRP3 did not correlate with magnitude of histone acetylation in macrophages. BHB reduced the NLRP3 inflammasome mediated IL-1β and IL-18 production in human monocytes. In vivo, BHB attenuates caspase-1 activation and IL-1β secretion in mouse models of NLRP3-mediated diseases like Muckle-Wells Syndrome (MWS), Familial Cold Autoinflammatory syndrome (FCAS) and urate crystal induce body cavity inflammation. Taken together, these findings suggest that the anti-inflammatory effects of caloric restriction or ketogenic diets may be mechanistically linked to BHB-mediated inhibition of the NLRP3 inflammasome, and point to the potential use of interventions that elevate circulating BHB against NLRP3-mediated proinflammatory diseases.

Iron formations are economically important sedimentary rocks that are most common in Precambrian sedimentary successions. Although many aspects of their origin remain unresolved, it is widely accepted that secular changes in the style of their deposition are linked to environmental and geochemical evolution of Earth. Two types of Precambrian iron formations have been recognized with respect to their depositional setting. Algoma-type iron formations are interlayered with or stratigraphically linked to submarine-emplaced volcanic rocks in greenstone belts and, in some cases, with volcanogenic massive sulfide (VMS) deposits. In contrast, larger Superior-type iron formations are developed in passive-margin sedimentary rock successions and generally lack direct relationships with volcanic rocks. The early distinction made between these two iron-formation types, although mimimized by later studies, remains a valid first approximation. Texturally, iron formations were also divided into two groups. Banded iron formation (BIF) is dominant in Archean to earliest Paleoproterozoic successions, whereas granular iron formation (GIF) is much more common in Paleoproterozoic successions. Secular changes in the style of iron-formation deposition, identified more than 20 years ago, have been linked to diverse environmental changes. Geochronologic studies emphasize the episodic nature of the deposition of giant iron formations, as they are coeval with, and genetically linked to, time periods when large igneous provinces (LIPs) were emplaced. Superior-type iron formation first appeared at ca. 2.6 Ga, when construction of large continents changed the heat flux at the core-mantle boundary. From ca. 2.6 to ca. 2.4 Ga, global mafic magmatism culminated in the deposition of giant Superior-type BIF in South Africa, Australia, Brazil, Russia, and Ukraine. The younger BIFs in this age range were deposited during the early stage of a shift from reducing to oxidizing conditions in the ocean-atmosphere system. Counterintuitively, enhanced magmatism at 2.50 to 2.45 Ga may have triggered atmospheric oxidation. After the rise of atmospheric oxygen during the GOE at ca. 2.4 Ga, GIF became abundant in the rock record, compared to the predominance of BIF prior to the Great Oxidation Event (GOE). Iron formations generally disappeared at ca. 1.85 Ga, reappearing at the end of the Neoproterozoic, again tied to periods of intense magmatic activity and also, in this case, to global glaciations, the so-called Snowball Earth events. By the Phanerozoic, marine iron deposition was restricted to local areas of closed to semiclosed basins, where volcanic and hydrothermal activity was extensive (e.g., backarc basins), with ironstones additionally being linked to periods of intense magmatic activity and ocean anoxia.Late Paleoproterozoic iron formations and Paleozoic ironstones were deposited at the redoxcline where biological and nonbiological oxidation occurred. In contrast, older iron formations were deposited in anoxic oceans, where ferrous iron oxid...

Low oxygen limited the rise of animals Oxygen levels in Earth's early atmosphere had an important influence on the evolution of complex life. Planavsky et al. analyzed the isotopic signature of chromium in sedimentary rocks from across the globe—a proxy for past oxygen levels. Oxygen levels in the mid-Proterozoic (1.6 billion to 900 million years ago) were very low: less than 0.1% of the modern atmosphere. These low levels were probably below the minimum oxygen requirements for the earliest animals, delaying their emergence and diversification. Science , this issue p. 635