12.2 The Geologic Time Scale

These flashcards cover key concepts regarding the geologic time scale, index fossils, and the relationship between mass extinction events and adaptive radiation.

What is the geologic time scale?

A representation of Earth's history organized by major changes and events using fossil and geological records.

What are the three basic units of time in the geologic time scale?

Eras, periods, and epochs.

What is an index fossil?

Fossils of organisms that existed during specific spans of time and are used to determine the age of rock layers.

What is the significance of the Cambrian Explosion?

It marks a relatively short period when all existing animal phyla developed.

Which period follows the Mesozoic Era?

The Cenozoic Era.

What defines the boundaries between many geologic periods?

Mass extinction events.

Why are fusulinids considered good index fossils?

They are abundant, widely distributed, easy to identify, and existed for a relatively brief time.

What does the term Paleozoic mean?

'Ancient life' - refers to the era characterized by early life forms.

What is adaptive radiation?

The diversification of a group of organisms into several species that adapt to different ecological niches.

How does mass extinction relate to adaptive radiation?

Mass extinctions create new ecological niches, leading to adaptive radiation as surviving species diversify.