What could have triggered mass extinctions of species in the past?

Explanation

### Step-by-Step Solution:

1. **Understanding Mass Extinction**:
- Mass extinction refers to a significant and rapid decrease in the number of species on Earth. This can occur due to various catastrophic events or changes in the environment.

2. **Climate Change**:
- One of the primary triggers for mass extinctions in the past has been climate change. This includes both extreme warming (global warming) and extreme cooling (ice ages). These changes can disrupt habitats and food sources, leading to the decline of species.

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