Many scientists call the Cambrian Explosion an 'evolutionary arms-race' to account for such a fast radiation. The adaptations that arose in the Cambrian were mainly for protection and predation. If one animal evolved a hard exoskeleton, another would have to evolve better predation strategies to survive.

What is the evolutionary significance of the Cambrian Explosion?

The Cambrian period, part of the Paleozoic era, produced the most intense burst of evolution ever known. The Cambrian Explosion saw an incredible diversity of life emerge, including many major animal groups alive today. Among them were the chordates, to which vertebrates (animals with backbones) such as humans belong.

Can the Cambrian Explosion be explained?

Oxygen fluctuations stalled life on Earth

Given the importance of oxygen for animals, researchers suspected that a sudden increase in the gas to near-modern levels in the ocean could have spurred the Cambrian explosion.