The Ordovician-Silurian extinction event was caused by global cooling and reduced sea levels.
Extinction may be defined as a phenomenon that includes the elimination or termination of a type of organism or of a group of individuals, usually a species as a result of various alterations.
It was the time when more than 85% of all the species on the earth's surface were extinct about 443 million years ago. This mass extinction is commonly known as the Ordovician-Silurian extinction.
This extinction event was caused due to the development of glacial conditions which ultimately leads to the reduction in sea level.
Therefore, the Ordovician-Silurian extinction event was caused by global cooling and reduced sea levels.
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