Igneous
131Silurian Period — Interval of geologic time, 443–417 million years ago. The third period of the Paleozoic Era, the Silurian follows the Ordovician Period and precedes the Devonian. It marks the first appearance of land plants and jawed fishes. The continents were… …
132Tertiary Period — Interval of geologic time, 65–1. 8 million years ago. It constitutes the first of the two periods of the Cenozoic Era, the second being the Quaternary. The Tertiary has five subdivisions: (from oldest to youngest) the Paleocene, Eocene, Oligocene …
