Michigan Test for Teacher Certification (MTTC) Secondary Integrated Science Practice test

What defines an era in geological time?

1. It is the shortest division of time

2. It is characterized by dominant plants and animals

3. It marks the complete extinction of all species

4. It is a time of widespread volcanic activity

The correct answer is: It is characterized by dominant plants and animals

An era in geological time is defined primarily by significant and widespread changes in the Earth's biosphere, which are often characterized by dominant plants and animals. These periods are established based on major events in Earth's history, such as mass extinctions or the emergence of distinct types of organisms. During an era, specific life forms thrive and significantly influence the planet's environment and geology. For example, the Mesozoic Era is known for the dominance of dinosaurs, while the Paleozoic Era features a rich diversity of marine life and early terrestrial plants. This biological prominence is crucial for distinguishing one era from another within the geological time scale. The other options do not accurately capture the essence of what defines an era. The shortest division of geological time is actually termed an "epoch," while the notion of complete extinction of all species would not be an accurate marker for an era since most eras encompass a variety of life forms and evolutionary developments. Lastly, while volcanic activity may occur during specific eras, it does not define the time period itself. Hence, the emphasis on dominant plants and animals provides the most accurate depiction of what characterizes an era.