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The end-Permian mass extinction (EPME) is associated with the loss of approximately 80–90 % marine species and 70 % terrestrial taxa. Massive greenhouse gas emissions from activities of the Siberian Traps Large Igneous Province (ST-LIP) and arc volcanisms are thought to be the trigger of the EPME. Global temperatures rose significantly following the EPME, and such extreme warmth persisted into the Early Triassic, which may have led to enhanced silicate weathering, and increased river runoff and sediment accumulation rate. However, ecosystem recovery was delayed by at least five million years after the EPME. One leading hypothesis attributes this protracted recovery to sustained atmospheric CO₂ accumulation, resulting from volcanic emissions from the ST-LIP that overwhelmed the normal Earth surface carbon cycle. To evaluate this, we synthesize geochemical and sedimentological records of continental weathering across the Permian–Triassic (PT) transition, drawing on a suite of proxies including major elements-based proxies, strontium (87/86Sr and δ88/86Sr), osmium (187Os/188Os), lithium (δ7Li), magnesium (δ26Mg) and calcium (δ44Ca) isotopes. We highlight the strengths and limitations of each proxy and assess how chemical and physical weathering may have responded to the environmental perturbations across the PT transition. Collectively, these records can help test the hypothesis that the silicate weathering feedback were insufficient to counteract elevated CO2 levels, thereby failing to stabilize Earth’s climate during the prolonged Early Triassic warmth. 

The timing, tempo, and causative mechanisms of Ocean Anoxic Event 1a (OAE1a), one of several such abrupt perturbations of the Mesozoic global carbon cycle, remain uncertain. Mudstones interbedded with tuffs in Hokkaido, Japan preserve carbon and osmium isotope shifts recording OAE1a. U-Pb zircon ages of tuffs constrain the OAE1a onset to 119.55 +0.072/−0.079 million years ago (Ma) and its duration to 1116 +87/−93 thousand years (kyr). Isotopic excursions of osmium followed by carbon that mark the rapid onset of OAE1a each lasted ~115 kyr. Critically, the occurrence of index fossilLeupoldina cabriin the Hokkaido OAE1a section, which also caps and thus postdate Ontong Java Plateau (OJP) basalts, has a U-Pb zircon age of ~118.7 to 118.4 Ma. Therefore, OJP volcanism remains a probable source of unradiogenic osmium and light carbon and a causative mechanism of OAE1a. 

Abstract Molecular phylogenetic data suggest that photosynthetic eukaryotes first evolved in freshwater environments in the early Proterozoic and diversified into marine environments by the Tonian Period, but early algal evolution is poorly reflected in the fossil record. Here, we report newly discovered, millimeter- to centimeter-scale macrofossils from outer-shelf marine facies of the ca. 950–900 Ma (Re-Os minimum age constraint = 898 ± 68 Ma) Dolores Creek Formation in the Wernecke Mountains, northwestern Canada. These fossils, variably preserved by iron oxides and clay minerals, represent two size classes. The larger forms feature unbranching thalli with uniform cells, differentiated cell walls, longitudinal striations, and probable holdfasts, whereas the smaller specimens display branching but no other diagnostic features. While the smaller population remains unresolved phylogenetically and may represent cyanobacteria, we interpret the larger fossils as multicellular eukaryotic macroalgae with a plausible green algal affinity based on their large size and presence of rib-like wall ornamentation. Considered as such, the latter are among the few green algae and some of the largest macroscopic eukaryotes yet recognized in the early Neoproterozoic. Together with other Tonian fossils, the Dolores Creek fossils indicate that eukaryotic algae, including green algae, colonized marine environments by the early Neoproterozoic Era.