### Permian-Triassic Extinction Models
The Permian-Triassic extinction event, which occurred approximately million years ago, resulted in the loss of over of marine species and of terrestrial species. Scientists have proposed different models to explain the primary cause of this mass extinction.
Model 1 (Volcanic Outgassing Model)
This model proposes that the extinction was triggered by massive, prolonged eruptions of the Siberian Traps, a large region of volcanic rock. These eruptions released vast quantities of carbon dioxide () and sulfur dioxide () into the atmosphere over hundreds of thousands of years. The resulting extreme greenhouse effect led to severe global warming and ocean acidification. The warming also depleted ocean oxygen, causing widespread marine anoxia that gradually suffocated marine life.
Model 2 (Bolide Impact Model)
This model proposes that the extinction was caused by the impact of a large asteroid or comet (a bolide). The collision instantly vaporized rocks, sending massive amounts of dust, pulverized rock, and sulfur aerosols into the stratosphere. This blocked sunlight, causing a rapid global drop in temperature ('impact winter') and halting photosynthesis. After the dust settled, the high levels of water vapor and vaporized greenhouse gases left in the atmosphere caused rapid global warming and acid rain, leading to a sudden, catastrophic collapse of ecosystems.
Which statement on the right correctly describes how each new scientific finding on the left supports or contradicts the proposed models?
- Finding A: Discovery of a global layer containing shock-metamorphosed quartz and microtektites dating precisely to the extinction boundary.Supports the Bolide Impact Model only, as the physical alterations in mineral structures require the extreme, instantaneous pressures of an impact.
- Finding B: High-precision zircon dating showing that the main phase of Siberian Traps eruptions occurred continuously for years, spanning the extinction event.Supports the Volcanic Outgassing Model only, as it demonstrates that the volcanic activity was active and sustained during the extinction window.
- Finding C: Fossil evidence showing that marine species sensitive to ocean acidification began dying out well before those sensitive only to temperature changes.Supports the Volcanic Outgassing Model over the Bolide Impact Model, as gradual selective extinction due to chemistry changes contradicts a sudden, non-selective physical impact event.