Auslöser für größtes Massenaussterben der Erdgeschichte identifiziert Neue Studie liefert umfassende Rekonstruktion der Perm-Trias-Grenze 19.10.2020/Kiel. Vor 252 Millionen Jahren starben am Übergang vom Erdzeitalter des Perm zu dem der Trias die meisten damals auf der Erde existierenden Lebensformen aus. Mit Hilfe neuester Analysemethoden und detaillierter Modellrechnungen ist es Wissenschaftlerinnen und Wissenschaftlern des GEOMAR Helmholtz-Zentrums für Ozeanforschung Kiel in Kooperation mit dem Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum und internationalen Partnern jetzt erstmals gelungen, die geochemischen Abläufe, die zu diesem Massenaussterben geführt haben, schlüssig nachzuvollziehen. Die Studie ist heute in der Fachzeitschrift Nature Geoscience erschienen.

We investigated the kill mechanisms of the end-Permian mass extinction by analyzing patterns in biomineralization of marine invertebrates. The microstructures of Upper Permian brachiopod organocarbonate shells show the demise of the production of fabrics with a columnar layer—which has less organic matrix—in favor of more organic-rich shells at the end of Permian. Also, in the 100–120 k.y. interval prior to the Permian-Triassic boundary (PTB), the Rhynchonellata had small calcite structural units (fibers) and thus a higher shell organic content, whereas the Strophomenata were not able to produce smaller units. This suggests that the two classes had a different capacity to cope with environmental change, with the Rhynchonellata being more able to buffer against pH changes and surviving the PTB, whereas the Strophomenata became extinct. The observed trends in biomineralization are similar to the patterns in extant marine invertebrates exposed to increasing pCO2 and decreasing pH, indicating that ocean acidification could have been one of the kill mechanisms of the mass extinction at the PTB.

A B S T R A C TShells of brachiopods are excellent archives for environmental reconstructions in the recent and distant past as their microstructure and geochemistry respond to climate and environmental forcings. We studied the morphology and size of the basic structural unit, the secondary layer fibre, of the shells of several extant brachiopod taxa to derive a model correlating microstructural patterns to environmental conditions. Twenty-one adult specimens of six recent brachiopod species adapted to different environmental conditions, from Antarctica, to New Zealand, to the Mediterranean Sea, were chosen for microstructural analysis using SEM, TEM and EBSD. We conclude that: 1) there is no significant difference in the shape and size of the fibres between ventral and dorsal valves, 2) there is an ontogenetic trend in the shape and size of the fibres, as they become larger, wider, and flatter with increasing age. This indicates that the fibrous layer produced in the later stages of growth, which is recommended by the literature to be the best material for geochemical analyses, has a different morphostructure and probably a lower organic content than that produced earlier in life.In two species of the same genus living in seawater with different temperature and carbonate saturation state, a relationship emerged between the microstructure and environmental conditions. Fibres of the polar Liothyrella uva tend to be smaller, rounder and less convex than those of the temperate Liothyrella neozelanica, suggesting a relationship between microstructural size, shell organic matter content, ambient seawater temperature and calcite saturation state.