ASBOG Practice Exam

What is the correct order of eons from oldest to youngest?

1. Hadean; Archean; Proterozoic; Phanerzoic

2. Archean; Hadean; Proterozoic; Phanerzoic

3. Phanerzoic; Archean; Hadean; Proterozoic

4. Proterozoic; Hadean; Archean; Phanerzoic

The correct answer is: Hadean; Archean; Proterozoic; Phanerzoic

The correct order of eons from oldest to youngest is accurately represented by the sequence: Hadean, Archean, Proterozoic, and Phanerzoic. The Hadean eon is the earliest period in Earth's history, starting with the formation of the planet around 4.6 billion years ago and lasting until about 4 billion years ago. It is characterized by a hot, molten surface and the formation of the Earth's earliest crust. Following the Hadean, the Archean eon spans from approximately 4 billion to 2.5 billion years ago, during which the Earth cooled further, allowing for the formation of stable continental crust and the emergence of the earliest known life forms, primarily simple single-celled organisms. The Proterozoic eon, extending from about 2.5 billion to 541 million years ago, saw the buildup of atmospheric oxygen and more complex life forms, including multicellular organisms. Lastly, the Phanerzoic eon began around 541 million years ago and continues to the present. This eon is marked by abundant fossil records and the evolution of diverse flora and fauna, leading to the rich biodiversity we observe today. This chronological understanding of Earth's history is fundamental in