Middle Eocene greenhouse warming facilitated by diminished weathering feedback

The Middle Eocene Climatic Optimum (MECO) represents a ~500-kyr period of global warming ~40 million years ago and is associated with a rise in atmospheric CO2 concentrations, but the cause of this CO2 rise remains enigmatic. Here we show, based on osmium isotope ratios (187Os/188Os) of marine sediments and published records of the carbonate compensation depth (CCD), that the continental silicate weathering response to the inferred CO2 rise and warming was strongly diminished during the MECO—in contrast to expectations from the silicate weathering thermostat hypothesis. We surmise that global early and middle Eocene warmth gradually diminished the weatherability of continental rocks and hence the strength of the silicate weathering feedback, allowing for the prolonged accumulation of volcanic CO2 in the oceans and atmosphere during the MECO. These results are supported by carbon cycle modeling simulations, which highlight the fundamental importance of a variable weathering feedback strength in climate and carbon cycle interactions in Earth’s history

A Meta‐Analysis on the Effects of Text Structure Instruction on Reading Comprehension in the Upper Elementary Grades

In this meta‐analysis, the authors synthesize results from 44 (quasi‐)experimental studies on informational and narrative text structure interventions involving students in grades 4–6 in regular school settings. Findings show that text structure instruction had positive immediate effects on students’ reading comprehension but that effect sizes varied largely across outcome measures: questions (Hedges’ g = 0.25), summarization (g = 0.57), recall (g = 0.37), and knowledge about text structure (g = 0.38). However, students who received text structure instruction no longer outperformed control groups at delayed posttests. Content‐related features, such as a focus on paragraph‐level structure, active construction of graphic organizers, and teaching rule‐based summarization techniques, moderated the effectiveness of text structure instruction, but these effects also varied across outcome measures. Instructional features moderated delayed effects: Interventions with opportunities for individual student practice resulted in higher delayed effects for comprehension questions. The authors argue that text structure instruction deserves a place in the primary school curriculum so the positive effects on reading will be maintained