Earth History Stories of Our Geological Past

As introduced in Chapter 9, from the beginning of the Paleozoic, life began to leave a much more tangible fossil record as well as experiencing major diversification during the Great Ordovician Biodiversity Event (Figure 9.24). Extinction events at the end of the Ordovician and the end of the Devonian decreased diversity by about 50%, but in each instance recovery to previous levels occurred within about five million years. The first part of this chapter reviews some of the major evolutionary events in the mid to later Paleozoic, with a particular focus on how the evolution of land plants paved the way for colonization by terrestrial animals and affected global climate, triggering a prolonged ice age. Massive volcanism reversed this trend and caused a hothouse at the end of the Paleozoic Era that initiated the most devastating of the five recorded mass extinctions known as the Great Dying and is the focus of the second part of the chapter.