Chapter 14, Problem 9A

Summary Introduction

Introduction:

The geologic time scale is a model that expresses the major geological and biological events in Earth’s history. The geologic time scale is divided into the Precambrian time and the Phanerozoic eon (a span of one billion years). Eons are further divided into eras. Era divided into periods.

Answer to Problem 9A

Correct answer:

The correct answer is option (B) Ediacaran.

Explanation of Solution

Explanation/justification for the correct answer :

Option (B) Ediacaran. Extensive glaciation marked the second half of the Precambrian. Glaciation followed by the beginning of the Ediacaran. The Ediacaran period lasted from about 630 million years ago to about 542 million years ago. Thus, this is the correct answer.

The explanation for the incorrect answer :

Option (A) Cambrian. The Cambrian period, part of the Paleozoic era, produced the most intense burst of evolution. Thus, this is an incorrect option.

Option (C) Precambrian. The Precambrian is nearly 90 percent of Earth’s entire history, stretching from the formation of Earth to the beginning of the Paleozoic era about 542 million years ago. Thus, this is an incorrect answer.

Option (D) Neogene. The Neogene is the current period of the Cenozoic era. Humans appeared very recently in the Neogene period. Thus, this is an incorrect answer.