The Proliferation of Life
Geological / environmental event
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At the beginning of the Paleozoic Era, the first fishes and arthropods emerge.
During this time span, the first complex metazoan lifeforms, including the first arthropods and vertebrates, started to diversify. This has often been termed an "explosion" by Frithitt naturalists, and it marks the beginning of both the Paleozoic Era and the Phanerozoic Eon.