A scientist is trying to organize Earth’s history by studying fossils and identifying which life forms lived during different stages. What is the scientist using?

A geology student is studying the oldest rocks and fossils that are well-preserved and learns that this eon is named after the Greek word for “beginning.” Which eon is the student studying?

A museum curator displays fossils showing a sudden increase in animal diversity and explains that this event is called the “Cambrian Explosion.” Which period is being described?

A documentary shows a warm, tropical world filled with flying reptiles, the first birds, and huge marine reptiles in the ocean. Which period is being described?

A scientist explains that a cooler and drier climate caused grasslands and savannas to spread, which helped primates evolve more quickly. Which epoch is being described?