Old Earth geological period, 542 to 488 million years ago; the first period of the Paleozoic era. It was followed by the Ordovician period.
The Cambrian has been called the "Age of Trilobites" because of the predominance of those primitive arthropods in the terragen fossil record. During this period there was the greatest adaptive radiation the pre-singularity Earth has seen, the Cambrian Explosion, when all existing (and many extinct) phyla of animals appeared for the first time. The climate was mostly mild, much of the earth's surface covered by warm shallow seas. The supercontinent Pannotia began to break into smaller continents. Land surfaces were barren, of complex life, consisting of deserts or of crusts of microbial life. The end of the Cambrian saw a mass extinction, with 50% of all animal families becoming extinct, possibly due to glaciation. At the same time as the Cambrian period was occurring on Earth, the unknown creators of Oceanus Ultimata were establishing that system.
Cambrian Explosion - Text by M. Alan Kazlev Period at the dawn of, or just preceding, the Cambrian period, when an unusual combination of environmental events (tectonic, atmospheric, ocean chemistry, climatic, ecological) triggered the sudden evolutionary radiation of terragen metazoa. These events are so unique and so distinctive that the term "Cambrian explosion" is used to refer to the sudden appearance of any higher ecologies and biota on a Gaian Type world previously only inhabited by microorganisms (or equivalent).
Proterozoic Eon - Text by M. Alan Kazlev Representing the "middle period" of the life-history of a Gaian Type world, with life mostly still at the microbial level. During this stage of planetary evolution, the atmosphere changes from reducing to oxygenated, the modern regime of continental drift begins, warm conditions replaced by "Snowball Earth", following that the short-lived Edicarian biota and the appearance of first metazoa (multicelluar animals). While the Earth was passing through it's Proterozoic stage, elsewhere in the galaxy, the Archivists, Mruta, Jacks, Halogenics, and very probably other significant xenosophont empires all arose and disappeared.