What happened at the start of the Cambrian Period?
A) the first oxygen-producing bacteria appeared
B) the first dinosaurs appeared
C) early humans first appeared
D) an explosion of genetic diversity appeared, leading to the appearance of the first animals

Question

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The start of the Cambrian Period, approximately 541 million years ago, is known as the "Cambrian Explosion." During this time, there was a sudden increase in genetic diversity and the appearance of the first animals, including many major groups that still exist today. This event marks an important point in the history of life on Earth. A and B are incorrect because both oxygen-producing bacteria and dinosaurs appeared much later in Earth's history. C is incorrect because early humans did not appear until approximately 2.8 million years ago, long after the Cambrian Period.

What Happened at the Start of the Cambrian Period