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Large impacts provide a mechanism for resurfacin g planets through mixing near-surface rocks with deeper material. Central peaks are formed from the dynamic uplift of rocks during crater formation. As crater size increases, central peak s transition to peak ri ngs. Without samples, debate surrounds the mechanics of peak-ring formation and their depth of origin. Chicxulub is the only known impact structure on Earth with an unequivocal peak ring, but it is buried and only accessible through drilling. Ex pedition 364 sampled the Chicxulub peak ring, which we found was formed from uplifted, fractured, shocked, felsic basement rocks. The peak-ring rocks are cross-cut by dikes and shear zones and have an unusually low density and seismic velocity. Large impacts therefore generate vertical fluxes and increase porosity in planetary crust

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As the surface ocean equilibrates with rising atmospheric CO 2 , the pH of surface seawater is decreasing with potentially negative impacts on coral calcification. A critical question is whether corals will be able to adapt or acclimate to these changes in seawater chemistry. We use high precision CT scanning of skeletal cores of Porites astreoides, an important Caribbean reef-building coral, to show that calcification rates decrease significantly along a natural gradient in pH and aragonite saturation (Ω arag ). This decrease is accompanied by an increase in skeletal erosion and predation by boring organisms. The degree of sensitivity to reduced Ω arag measured on our field corals is consistent with that exhibited by the same species in laboratory CO 2 manipulation experiments. We conclude that the Porites corals at our field site were not able to acclimatize enough to prevent the impacts of local ocean acidification on their skeletal growth and development, despite spending their entire lifespan in low pH, low Ω arag seawater.reef framework | caribbean corals acidic springs S cleractinian corals, whose calcium carbonate (CaCO 3 ) skeletons provide the structural framework of coral reef ecosystems, are subject to numerous direct and indirect stressors and are facing steep global decline (1-3). As the ocean absorbs anthropogenic CO 2 , surface ocean pH and the availability of carbonate ions to corals and other reef calcifiers are decreasing (1-5). Global climate models predict a drop of 0.3 pH units, from 8.1 to 7.8 by the end of the 21st century (6-8), resulting in a 50% reduction in carbonate ion concentration (9). Consequently, it is predicted that ocean acidification will result in a widespread reduction in coral calcification by the year 2065 (10), causing large-scale reef degradation and loss (11).The predicted response of coral reef calcification to decreasing aragonite-saturation (Ω arag ) state is based primarily on model calculations of future Ω arag (6,7,9,12) and the observed response of coral calcification to low Ω arag in short-term laboratory-based or mesocosm carbonate chemistry manipulation experiments (11, 13-16). Additionally, field-based observations of net coral reef ecosystem calcification responses to changes in Ω arag state in situ also suggest declines in calcification (17-21). However, key questions remain regarding the acclimation and adaptation potential of coral calcification to ocean acidification. Acclimatization, or the potential for an organism to adjust to changes in an environment via physical modifications, is distinguished from adaptation, or permanent evolutionary modifications made by an organism in response to repeated stressors. Specifically, an outstanding question is whether corals will be able to acclimate or adapt to maintain sufficient rates of calcification to sustain the reef structure (17,22,23). To address these questions, field-based studies where corals have been naturally exposed to chronic low pH conditions for extended periods could provide important new ins...

The Cretaceous/Palaeogene mass extinction eradicated 76% of species on Earth. It was caused by the impact of an asteroid on the Yucatán carbonate platform in the southern Gulf of Mexico 66 million years ago , forming the Chicxulub impact crater. After the mass extinction, the recovery of the global marine ecosystem-measured as primary productivity-was geographically heterogeneous ; export production in the Gulf of Mexico and North Atlantic-western Tethys was slower than in most other regions, taking 300 thousand years (kyr) to return to levels similar to those of the Late Cretaceous period. Delayed recovery of marine productivity closer to the crater implies an impact-related environmental control, such as toxic metal poisoning , on recovery times. If no such geographic pattern exists, the best explanation for the observed heterogeneity is a combination of ecological factors-trophic interactions , species incumbency and competitive exclusion by opportunists -and 'chance'. The question of whether the post-impact recovery of marine productivity was delayed closer to the crater has a bearing on the predictability of future patterns of recovery in anthropogenically perturbed ecosystems. If there is a relationship between the distance from the impact and the recovery of marine productivity, we would expect recovery rates to be slowest in the crater itself. Here we present a record of foraminifera, calcareous nannoplankton, trace fossils and elemental abundance data from within the Chicxulub crater, dated to approximately the first 200 kyr of the Palaeocene. We show that life reappeared in the basin just years after the impact and a high-productivity ecosystem was established within 30 kyr, which indicates that proximity to the impact did not delay recovery and that there was therefore no impact-related environmental control on recovery. Ecological processes probably controlled the recovery of productivity after the Cretaceous/Palaeogene mass extinction and are therefore likely to be important for the response of the ocean ecosystem to other rapid extinction events.