The Cambrian explosion is theorized to have come about because the earth had been undergoing a great climactic change. There is a hypothesis that oxygen was being mixed into the ocean and creatures were forced to adapt quickly to the harsh surroundings.

In the Cambrian explosion, the appearance of limbs and segmented bodies occurred for the first time. Until this event, it is hypothesized that there were no predators, and now for the first time, they existed. Organisms with hard body parts had begun to appear, such as the trilobites, brachiopods, archaeocyathids, hyolithids, and those simply termed by the scientists as the small shelly organisms. All life was aquatic at this time.

The Burgess Shale is very important evidence of the Cambrian explosion. This is because many Cambrian fossils are found in it. One of the sites includes the British Columbian Rocky Mountains, in western Canada. It is significant because it was able to preserve soft-bodied fossils along with the hard-bodied organisms that are typically fossilized. In it, there are many unusual forms of organisms fossilized, almost nothing resembling what exists today.

An Atrypa Hinge, which is a type of brachiopod.