Question

### Late Ordovician Mass Extinction Models

The Late Ordovician Mass Extinction (LOME), which occurred approximately $444$ million years ago, resulted in the loss of about $85\%$ of marine species. Scientists have proposed different models to explain the primary cause of this extinction event.

**Model $1$ (Glaciation/Cooling Model)**
This model proposes that the growth of the Gondwanan ice sheet triggered the extinction. The accumulation of ice locked up global water, leading to a rapid eustatic sea-level fall of over $100\text{ meters}$. This regression drained shallow, warm epicontinental seas, which hosted the vast majority of marine life. Furthermore, global temperatures plunged, and the cooling of tropical waters eliminated species adapted to warm climates. In this view, habitat loss due to sea-level drop and direct thermal stress from cooling were the sole triggers of the first extinction pulse.

**Model $2$ (Anoxia/Volcanism Model)**
This model proposes that large-scale volcanic eruptions from a large igneous province triggered the extinction. The eruptions released massive amounts of carbon dioxide ($CO_2$) and sulfur dioxide ($SO_2$) into the atmosphere, causing short-term acid rain followed by long-term global warming due to the greenhouse effect. Warming reduced the solubility of oxygen in seawater, and increased weathering washed nutrients into the oceans, causing widespread marine anoxia (oxygen depletion). Acidification of the oceans further prevented calcifying organisms from building shells. In this view, oxygen starvation (anoxia) and ocean acidification were the primary causes of the mass extinction.

A geologist compiles several hypotheses regarding the environmental conditions and mechanisms that drove the Late Ordovician Mass Extinction. Match each hypothesis to the model (Model $1$, Model $2$, or both) that supports it.