Life Through the Ages

During the Cambrian Period, the supercontinent of Rodinia began to fragment and the climate was mild, but land was still barren without land plants. Ocean oxygen levels rose, and skeletonized, mobile animals evolved in a rapid diversification event called the “Cambrian Explosion.” Many animal groups appeared for the first time during this period.

During much of this period, areas of what would become North America were covered by shallow seas. Marine organisms diversified in this period, increasing the number of species. The earliest evidence of land plants comes this period, and they may have caused the expansion of glaciers in the Late Ordovician. One of the “Big Five” extinctions occurred at the end of this period.

During the Devonian Period, oxygen levels approached modern day levels and coincided with an explosion of floral and faunal life. The first tetrapods and the first jawed fish also appeared during this time. Marine life during this time was dominated by brachiopods and corals. At the end of the Devonian, there was another mass extinction which predominantly affected marine life.

The Earth during the Permian period consisted of a large, arid supercontinent called Pangea surrounded by a single ocean. In this ocean, brachiopods and ammonoids thrived, but corals were lessening. All of these groups are represented in this diorama. The Permian period ended with the Earth’s largest mass-extinction event, in which almost 90% of all species went extinct. 

During the Triassic period, a large landmass called Pangea persisted, and diversity slowly recovered from the End-Permian extinction. Ferns and gymnosperms, particulalrly cycads, were common, and dinosaurs evolved in this period. 

During the Cretaceous Period, the Americas moved away from Eurasia and Africa as the Atlantic ocean expanded. In the oceans, mollusks thrived, while brachiopods declined and corals begin to look more like their modern relatives. This period ended when a large asteroid or comet hit Earth causing the second largest mass extinction event observed in the fossil record.