Soru

The Late Devonian mass extinction (approximately 372 million years ago) is characterized by a major loss of marine biodiversity and elevated concentrations of mercury ($Hg$) in sedimentary layers globally. Three hypotheses discuss the triggers and mechanisms of this extinction event.

Hypothesis 1
The extinction was triggered by the eruption of the Viluy Large Igneous Province (LIP). Massive volcanic eruptions released large volumes of carbon dioxide ($CO_2$) and gaseous $Hg$ into the atmosphere. The greenhouse effect from $CO_2$ caused rapid global warming and ocean stratification, leading to widespread marine anoxia (lack of oxygen). Meanwhile, atmospheric deposition of $Hg$ created global spikes in sedimentary mercury, poisoning marine ecosystems.

Hypothesis 2
The extinction was caused by a major asteroid impact. The impact vaporized target rocks, ejecting dust and sulfur compounds into the stratosphere, which blocked sunlight and caused a severe "impact winter" (global cooling). Acid rain from sulfur aerosols accelerated continental weathering, washing deep-seated terrestrial $Hg$ deposits into the oceans. This resulted in elevated sedimentary $Hg$ deposition and poisoned shallow marine habitats.

Hypothesis 3
The extinction was driven by sea-level fluctuations that forced deep, oxygen-depleted, and toxic hydrogen sulfide-rich ($H_2S$) waters onto shallow continental shelves. This toxic upwelling directly suffocated marine life. The high affinity of mercury for organic matter and sulfides caused $Hg$ already present in the ocean to bind rapidly to organic-rich sediments on the shelves, creating an apparent sediment $Hg$ anomaly without requiring any global atmospheric source of mercury.

Match each scientific statement with the combination of viewpoints that supports it.