The Cambrian Period – other geologic times also shown in photographs (Isle La Motte)
The Cambrian period occurred approximately 542-488 million years ago, and included the biggest evolutionary explosion in Earth’s history. Some researchers think this happened due to a combination of a warming climate, more oxygen in the ocean, and the creation of extensive shallow-water marine habitats—which, combined, made an ideal environment for the proliferation of new types of animals, including animals that were larger and more complex in their body shapes and ecologies than their ancestors.
Credit: Smithsonian Institution