Question

Fossils of most of the modern animal phyla first appeared over a short period of time. In which one of the following geological time periods did this occur?

• A. Cambrian
• B. Cretaceous
• C. Jurassic
• D. Permian

Hint:

The Cambrian Explosion refers to the sudden appearance of most major animal phyla around 541 million years ago, marking a significant event in evolutionary history.

Answer 1

The Correct Option is A

Step 1: Understand the Cambrian Explosion. 
The Cambrian period, around 541 million years ago, marked a significant event in the history of life on Earth called the "Cambrian Explosion." During this time, most of the major animal phyla appeared in a relatively short period of time in evolutionary terms. 
Step 2: Analyze the geological time periods. 
The Cretaceous, Jurassic, and Permian periods did not experience such a rapid appearance of animal phyla as seen in the Cambrian period.
The correct answer is therefore the Cambrian period, as it is associated with the sudden emergence of diverse life forms.
Thus, the correct answer is Cambrian.