ASBOG Practice Exam

How many eons is the Precambrian divided into?

1. Four

2. Three

3. Two

4. Five

The correct answer is: Three

The Precambrian, which encompasses approximately 88% of Earth's geological history, is divided into three eons: the Hadean, Archean, and Proterozoic. This division reflects the significant geological and biological developments that occurred during these vast time periods. The Hadean eon predates the formation of the earliest known rocks and is characterized by the planet's cooling and the formation of the first solid crust. The Archean eon follows, marked by the emergence of the oldest known rock formations and the first appearance of simple life forms, such as prokaryotic microorganisms. Finally, the Proterozoic eon spans from about 2.5 billion years ago to the beginning of the Cambrian period, featuring significant events such as the buildup of atmospheric oxygen and the emergence of multicellular life forms. Understanding this division is crucial for studying the geological and biological processes that have shaped Earth throughout its history.