See also: Organic, Archaean, Aerobic, Complex Ocean, Simple Land, Complex Land, Extensive
The Archaean classification covers single celled organisms up until the evolution of plants and animals (algae, sponges and plankton). Most such worlds will be full of metazoan life in the form of bacteria, and is named after the Archaean period on Earth. It may last around a billion years.
The success of bacteria can prevent the evolution of more complex life. Anaerobic bacteria initially prevent the build up of oxygen in the oceans.
Life on these worlds has arisen, and simple single celled life, in the form of Simple Organics has taken hold. A world often remains in this state for a billion years or so.
Base Organics is simple non-living organic matter.
Simple Organics are the first life forms, and may dominate for a few hundred million years until the first bacteria evolve.
Metazoa are normally the most common form of life on such worlds, and can dominate for over a billion years.