Question

### Passage

The Paleocene-Eocene Thermal Maximum (PETM) Carbon Excursion

Approximately 56 million years ago, Earth experienced the Paleocene-Eocene Thermal Maximum (PETM), characterized by a rapid global temperature rise of $5^\circ\text{C}$ to $8^\circ\text{C}$ and a massive negative carbon isotope excursion (CIE), indicating a large injection of light carbon ($^{12}\text{C}$-enriched) into the ocean-atmosphere system. Three hypotheses propose different primary mechanisms for this event.

*Hypothesis 1 (Methane Hydrate Dissociation)*
Initial gradual warming, triggered by orbital variations and volcanic outgassing, warmed deep ocean currents. This warming destabilized submarine methane hydrates ($CH_4 \cdot H_2O$) trapped in continental slope sediments. The sudden release of oceanic methane ($CH_4$), which has an extremely light isotopic signature ($\delta^{13}\text{C} \approx -60\text{‰}$), led to rapid oxidation in the water column and atmosphere, converting the methane into carbon dioxide ($CO_2$). This process depleted oceanic oxygen, caused widespread ocean acidification, and amplified global warming via the greenhouse effect.

*Hypothesis 2 (Terrestrial Carbon Combustion)*
A prolonged period of severe regional drought, combined with orbitally induced seasonal extreme temperatures, lowered water tables in high-latitude peatlands. This dried out massive reservoirs of terrestrial organic matter, including peat and shallow coal deposits. Extensive, deep-burning wildfires swept across these regions, combusting vast quantities of terrestrial organic carbon ($\delta^{13}\text{C} \approx -25\text{‰}$ to $-30\text{‰}$) directly into the atmosphere as $CO_2$ and carbon monoxide ($CO$). The combustion released soot and greenhouse gases, causing rapid atmospheric warming and subsequent ocean acidification as atmospheric $CO_2$ dissolved into the surface ocean.

*Hypothesis 3 (Thermogenic Methane Generation)*
The emplacement of the North Atlantic Igneous Province (NAIP) involved large-scale intrusions of basaltic magma (sills) into organic-rich sedimentary basins, particularly Cretaceous shales. The extreme heat of the magma thermally cracked the sedimentary organic matter, generating vast quantities of thermogenic methane gas ($\delta^{13}\text{C} \approx -35\text{‰}$ to $-45\text{‰}$) and $CO_2$. These gases migrated upward through hydrothermal vent complexes, venting directly into the atmosphere and deep ocean. This rapid, crustally driven release of light carbon acidified the oceans and drove global greenhouse warming.

Based on the hypotheses presented, match each scientific proposition on the left with the correct level of support on the right.