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.

Common atmosphere types are:

• Primordial
• Nitrogen Compounds
• Low Oxygen

Archaean worlds contain life, but it is very simple.

It inherits the basic non-living material from which life is formed, which are found in large quantities on Organic worlds:

• Organic Chemicals - Basic non-living organic material.

The exact path that evolution takes on each world is different, but there are certain stages which are passed through from simple to more complex life forms.

• Prokaryotes - These are the simplest unicellular organisms, such as bacteria. They are the first life forms to evolve on most worlds.
• Protozoa - These are single celled organisms which are more complex than bacteria. They have mobility and feed on external chemicals, making them very basic animals. They are generally sub-millimetre in size.
• Algae - Range from singled celled to simple multi-celled plant life, though are generally small (millimetre scale). They are photosynthetic, turning sunlight into oxygen.

Prokaryotes → Algae / Protozoa