Class M planets range in age from 3 to 10 billion years old. Their diameters range in size from 10,000 to 15,000 km. They are always located in the ecozone region of a star's solar system. Their surfaces are comprised with a relatively thin tectonic layer floating on a molten rock mantle, usually with active volcanoes present. Class M planets have an abundant amount of water necessary for life to exist. Their atmospheres contain oxygen/nitrogen with other trace gases. Life forms are almost always present, flourishing as extensive plant and animal life. Usually a sentient race is also present.