Which period occurred about 438 mya when 75 percent of species disappeared?

The period that occurred about 438 million years ago and saw the disappearance of approximately 75 percent of species is known as the Late Ordovician mass extinction. This event was primarily caused by significant climate changes, including glaciation and a drop in sea levels, which drastically altered habitats. It was one of the five major mass extinctions in Earth's history and had a profound impact on marine life, particularly affecting brachiopods and trilobites.