ASBOG Practice Exam

What is the chronological order of the eons in the Precambrian?

1. Proterozoic, Archean, and Hadean

2. Hadean, Archean, and Proterozoic

3. Archean, Proterozoic, and Hadean

4. Phanerozoic, Hadean, and Archean

The correct answer is: Hadean, Archean, and Proterozoic

The correct answer places the eons in their appropriate chronological order as understood in the geological time scale. The Hadean eon is recognized as the earliest period of Earth's history, lasting from the formation of the Earth around 4.6 billion years ago until about 4 billion years ago. This eon is characterized by extreme volcanic activity and the creation of the first solid crust. Following the Hadean, the Archean eon spans from approximately 4 billion to 2.5 billion years ago. During this period, the Earth's crust stabilized enough to support the appearance of the first known continental land masses, and it is within this eon that life is believed to have first emerged, primarily in the form of simple prokaryotic organisms like bacteria. The Proterozoic eon comes next, lasting from about 2.5 billion to 541 million years ago. This eon witnessed significant geological, atmospheric, and biological changes, including the buildup of atmospheric oxygen and the emergence of more complex life forms. This sequence—Hadean, Archean, and Proterozoic—reflects the increasing complexity and stability of the Earth over time, marking key developments in both geological and biological history. Understanding this chronological order