Ordovician

During the Ordovician period, marine life continued to thrive and diversify. The seas were dominated by invertebrates such as trilobites, brachiopods, bryozoans, and the first coral reefs, formed by coral-like organisms. The period also saw the rise of the first cephalopods, the ancestors of modern squids and octopuses, which became the top predators in marine ecosystems. Additionally, the first evidence of land plants appeared, marking a significant step in the colonization of terrestrial environments.

Geologically, the continents continued to drift, and most of the world’s landmasses were located in the Southern Hemisphere. Gondwana, a supercontinent, began to move toward the South Pole, contributing to the cooling of the Earth’s climate toward the end of the period. The global cooling event triggered a series of glaciations, especially in the southern supercontinent, which caused sea levels to drop dramatically. This led to the Ordovician-Silurian extinction event, during which about 85% of marine species were wiped out, particularly those inhabiting shallow, warm waters.

This mass extinction is thought to have been caused by both the rapid onset of glaciation and subsequent changes in sea levels, which disrupted marine habitats. It marks one of the five largest extinction events in Earth’s history.