End-Ordovician Extinction

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The End-Ordovician Extinction, one of the "Big Five" mass extinctions, occurred approximately 443 million years ago. It is characterized by two distinct phases of extinction, roughly a million years apart. The event resulted in the loss of about 85% of marine species, including significant declines in trilobites, brachiopods, corals, and graptolites. The primary cause was climate change, specifically a major ice age centered in Gondwana, which led to global cooling and drastic sea-level drops. These environmental changes had devastating effects on marine life adapted to warmer conditions. The glaciation caused shallow seas to drain, eliminating habitats and further exacerbating extinctions. Volcanic activity and the emergence of terrestrial plants, which reduced atmospheric CO2, are also proposed as contributing factors. The extinction marked a significant shift in Earth's biodiversity, impacting the trajectory of metazoan life and setting the stage for the evolution of new species in the Silurian period.