1. The Eras of Geologic Time
... 's mountain chains. One of the most important features of this period is the appearance of nearly all of the invertebrate animal phyla in abundance. A few fishlike invertebrates and vertebrates appeared in the Cambrian and Ordovician. Scorpions, land invertebrates, amphibians, land reptiles and marine reptiles also appeared. Reptiles increased in number and plant life reached its climax. Great crystal commotion marked the end of the Paleozoic era ... and the beginning of the topography of North America. The Mesozoic era marks a major division of geologic time from sixty five to two hundr...
- Word Count: 1841
- Approx Pages: 7
- Grade Level: Undergraduate