Cambrian Explosion

The Cambrian Explosion of life marked the start of the Cambrian period on Earth circa 542 million BCE. After billions of years of single-celled organisms, evolution gave rise to thousands of species of hard-shelled multicellular creatures, most of which lived on the floor of the warm shallow seas that dominated the planet The only life on the surface consisted of lichen and algae; plants would not evolve for millions more years. (PROSE: Prehistory Repeating Itself ^[+]Loading...["Prehistory Repeating Itself (feature)"])