Soru

For decades, paleoceanographers attributed the sudden end-Permian mass extinction primarily to intense volcanic activity in the Siberian Traps, which unleashed massive quantities of greenhouse gases and sulfur dioxide. Skeptics of this mantle-plume hypothesis, however, contend that volcanic outgassing alone fails to account for the abruptness of the marine die-off recorded in sediment cores, pointing out that catastrophic volcanic episodes typically produce gradual, protracted ecological shifts rather than sudden biotic collapse. To reconcile this discrepancy, supporters of the volcanic model have recently proposed that basaltic lava flows intruded into carbon-rich sedimentary basins, releasing vast volumes of thermogenic methane that accelerated global warming.

Critics have counterargued that if thermogenic methane driving ocean acidification were the primary driver of extinction, calcifying marine organisms should show severe, uniform mortality worldwide prior to non-calcifying species. However, recent high-resolution isotopic analysis of equatorial limestone deposits reveals that while calcifiers suffered disproportionately in shallow surface waters, deep-water non-calcifying benthic communities collapsed concurrently. This synchronicity suggests that catastrophic deep-ocean hypoxia—triggered by thermal stratification and delayed nutrient turnover—operated alongside surface acidification. Thus, the argument that differential mortality rules out thermogenic methane ignores how thermal stratification unifies these distinct kill mechanisms. Rather than invalidating the volcanic-intrusion model, the evidence of concurrent deep-water collapse demonstrates that the counterargument relies on a flawed assumption of uniform ocean chemistry.

Based on the passage, the author addresses the critics' counterargument regarding the pattern of marine mortality primarily by doing which of the following?