Life over Time

Table 38-2 shows life-forms in relation to geological time in a manner somewhat different from that employed in table 38-1. The bacteria, algae, and fungi are shown to be stabilized, remaining essentially constant in numbers of forms across time. The club mosses were much more abundant in the Devonian and Carboniferous periods, and became much diminished as the Mesozoic era approached. The same is shown for the horsetails. The ginkgoes were more abundant during the first half of the Mesozoic era, and today are represented by a single form, Ginkgo biloba. Coniferous trees had their time of dominance in the Mesozoic era, and the angiosperms appeared in more recent times, at the beginning of the Cenozoic era.

Table 38-2 Geological Time Chart Showing The Rise and Decline of Various Plant Forms.