Question

### Models of the Cretaceous-Paleogene (K-Pg) Extinction Event

Around 66 million years ago, a mass extinction event wiped out approximately 75% of all species on Earth, including the non-avian dinosaurs. Scientists have proposed different models to explain the primary cause of this event.

Model 1 (Asteroid Impact)

This model asserts that a single, large asteroid (approximately 10 kilometers in diameter) struck Earth at Chicxulub (in modern-day Mexico). The high-velocity impact ejected enormous volumes of dust, pulverized rock, and sulfate aerosols into the stratosphere. This blocked incoming sunlight, initiating a rapid "impact winter" that halted photosynthesis globally within weeks. The sudden collapse of primary production caused a catastrophic, rapid collapse of the food web. The extinction was globally synchronized and occurred over a very short geological timespan (years to decades).

Model 2 (Deccan Traps Volcanism)

This model asserts that the primary driver of the extinction was the eruption of the Deccan Traps, a massive flood basalt province in modern-day India. The eruptions occurred in multiple intense pulses spanning roughly 800,000 years, straddling the extinction boundary. These eruptions released massive volumes of greenhouse gases, mainly carbon dioxide ($CO_2$) and sulfur dioxide ($SO_2$), into the atmosphere. The long-term accumulation of these gases caused severe global warming cycles alternating with brief acid-rain cooling events, along with widespread ocean acidification. The extinction was a gradual process spanning tens of thousands of years, driven by progressive ecological instability.

Based on the descriptions of Model 1 and Model 2, which of the following statements best describes how the two models differ regarding the atmospheric changes that led to the extinction?