Color enhanced fossil record of early Cambrian times. Depicted are arthropods (D and K - O), mollusks (B, E and perhaps, F and G), brachiopods (I, J), echinoderms (H), sponges (A), and other organisms such as (C) that probably belong to phyla, or animal groups, that became extinct long ago. The Cambrian is the first geological period of the Paleozoic Era (1.9 million years ago). The rapid diversification of lifeforms in the Cambrian, known as the Cambrian explosion, produced the first representatives of many modern phyla.