The Ordovician is a geological period that lasted from about 485 to 444 million years ago. It follows the Cambrian period and precedes the Silurian period. During this time, the Earth experienced significant changes, including the diversification of marine life and the first appearance of land plants. The Ordovician is known for its rich fossil record, particularly of trilobites, brachiopods, and graptolites. The period ended with a major extinction event, which wiped out nearly 85% of marine species, marking one of the largest mass extinctions in Earth's history.