The Hirnantian Stage is the last stage of the Ordovician Period, occurring around 445 to 443 million years ago. It is characterized by a significant drop in sea levels and a dramatic global cooling event that led to one of the largest mass extinctions in Earth's history. This stage marks the transition from the Ordovician to the Silurian Period and is crucial for understanding both paleoclimatic conditions and biodiversity during this time.
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