The form and function of plants. Can be used
as a map unit.
Configuration of the earth's surface, its geologic features (parent material), and landforms (mountains, plains, valleys, lowlands). Texas is tightly linked to this.
The present epoch which began about 10,000 years ago, after the retreat of the ice of the last glaciation, and is sometimes regarded as another interglacial period.
Began two million to 11 thousand years ago; extensive glaciation of the northern hemisphere; the time of human evolution.
The current geological age, viewed as having begun about 200 years ago with the significant impact of human activity on the ecosphere.