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The chronology of the Paleocene-Eocene Thermal Maximum (PETM, ~56 Ma) remains disputed, hampering complete understanding of the possible trigger mechanisms of this event. Here we present an astrochronology for the PETM carbon isotope excursion from Howards Tract, Maryland a paleoshelf environment, on the mid-Atlantic Coastal Plain. Statistical evaluation of variations in calcium content and magnetic susceptibility indicates astronomical forcing was involved and the PETM onset lasted about 6 kyr. The astrochronology and Earth system modeling suggest that the PETM onset occurred at an extreme in precession during a maximum in eccentricity, thus favoring high temperatures, indicating that astronomical forcing could have played a role in triggering the event. Ca content data on the paleo-shelf, along with other marine records, support the notion that a carbonate saturation overshoot followed global ocean acidification during the PETM. Astrochronology of a core in Maryland suggests that the onset of the Paleocene-Eocene Thermal Maximum (PETM) warming lasted about 6 thousand years. These data are more consistent with astronomical forcing than an extraterrestial trigger for the PETM. [ABSTRACT FROM AUTHOR]

To fully assess the resilience and recovery of life in response to the Cretaceous–Paleogene (K-Pg) boundary mass extinction ~ 66 million years ago, it is paramount to understand biodiversity prior to the Chicxulub impact event. The peak ring of the Chicxulub impact structure offshore the Yucatán Peninsula (México) was recently drilled and extracted a ~ 100 m thick impact-generated, melt-bearing, polymict breccia (crater suevite), which preserved carbonate clasts with common biogenic structures. We pieced this information to reproduce for the first time the macrobenthic tracemaker community and marine paleoenvironment prior to a large impact event at the crater area by combining paleoichnology with micropaleontology. A variable macrobenthic tracemaker community was present prior to the impact (Cenomanian–Maastrichtian), which included soft bodied organisms such as annelids, crustaceans and bivalves, mainly colonizing softgrounds in marine oxygenated, nutrient rich, conditions. Trace fossil assemblage from these upper Cretaceous core lithologies, with dominant Planolites and frequent Chondrites, corresponds well with that in the overlying post-impact Paleogene sediments. This reveals that the K-Pg impact event had no significant effects (i.e., extinction) on the composition of the macroinvertebrate tracemaker community in the Chicxulub region. [ABSTRACT FROM AUTHOR]

Pteropods have been a key focus of ocean acidification studies during the last decade due to their fragile aragonite shells and key role they play in polar ecosystems. Pteropods collected at sea are typically preserved before analysis at onshore laboratories. Despite the importance placed on pteropods as a sentinel for the impact of ocean acidification on marine calcifiers, there has never been a systematic study assessing how different preservation techniques affect the condition of pteropod shells. In this study we perform an experiment to assess the impact of six preservation techniques on the shell condition of Limacina retroversa pteropods. Using five shell condition-assessment methods, we find shells that were air dried were the least altered relative to the time of collection. Of the solution-based preservation techniques, shells were least altered when preserved in 70% buffered ethanol and most altered in a solution of sodium chloride buffered formalin. Our results have implications for the interpretation of pteropod shell condition in samples which have been stored in solution, and provide guidelines for the preservation of future pteropod collections. [ABSTRACT FROM AUTHOR]

The Cretaceous/Palaeogene mass extinction eradicated 76% of species on Earth1,2. It was caused by the impact of an asteroid3,4 on the Yucatán carbonate platform in the southern Gulf of Mexico 66 million years ago5, forming the Chicxulub impact crater6,7. After the mass extinction, the recovery of the global marine ecosystem—measured as primary productivity—was geographically heterogeneous8; export production in the Gulf of Mexico and North Atlantic-western Tethys was slower than in most other regions8-11, 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 poisoning12, on recovery times. If no such geographic pattern exists, the best explanation for the observed heterogeneity is a combination of ecological factors—trophic interactions13, species incumbency and competitive exclusion by opportunists14—and ‘chance’8,15,16. 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. Micro- and nannofossil, trace fossil and geochemical evidence from the Chicxulub impact crater demonstrates that proximity to the asteroid impact site did not determine rates of recovery of marine ecosystems after the end-Cretaceous mass extinction. [ABSTRACT FROM AUTHOR]

This article discusses the role of volcanism in a period of oxygen deprivation, or anoxia, in the oceans during the Cretaceous period. This period of volcanism resulted in mass extinctions of oceanic life and the creation of the large igneous province, which forms the floor of the Caribbean Sea. Two hypotheses, which are not mutually exclusive, regarding the relationship between volcanism and anoxia are noted. The first relates to the release of iron by volcanism, which caused a plankton bloom and later anoxic conditions as the plankton decomposed. The second hypothesis is that global warming led to anoxia.

This study aimed to examine the effect of four types of assessment on overall student success in an online college-level climate change course. Quizzes, midterms, lab assignments, and a capstone project as well as knowledge check questions were used to assess different aspects of student learning, consistent with Bloom’s taxonomy hierarchy. Quizzes and midterms assess basic knowledge, including remembering and understanding concepts, laboratory assignments require students to analyze and integrate concepts, and the capstone allows students to evaluate their understanding and create new content. Binary logistic regression, multiple regression analysis, continuous-by-continuous interaction modeling, and path analysis were used to investigate the moderating and mediating effects of these assessment types. We found both direct and indirect positive interactions as well as one negative interaction. Positive interactions were identified between quiz and lab assignment achievement and between capstone achievement and lab assignment achievement. The total score for correctly answered knowledge check questions positively affected quiz and lab assignment achievements. The interaction between capstone project achievement and total score for correctly answered knowledge check questions showed a negative interaction. Finally, the total score for correctly answered knowledge-check questions had an indirect positive effect on overall student success in the course. Results show that different types of assessment in an online course are complementary and amplify student learning. [ABSTRACT FROM AUTHOR]

Reconstruction from oxygen-isotope data of global sea-surface temperatures (SSTs) that prevailed during periods when greenhouse-gas levels were higher than at present (that is, in the early Eocene and Cretaceous epochs) indicates that temperatures were significantly warmer than present in mid- to high latitudes, but similar to or slightly cooler in the tropics. However, Pearson and colleagues claim, on the basis of oxygen-isotope data from planktonic foraminifers recovered from clay beds in Tanzania and other localities, that the tropics were warm during the Eocene, attributing the discrepancy between these and previous tropical SST estimates to the effects of diagenetic overprinting of the latter. Here we note some potential flaws in their interpretation of the new oxygen-isotope data. [ABSTRACT FROM AUTHOR]