They are defined by Edward O. Wilson as "unique assemblages of bacteria and fungi that occupy pores in the interlocking mineral grains of igneous rock beneath Earth's surface.
"[1] Endolithic systems are still at an early stage of exploration.
In some cases its biota can support simple invertebrates; in most, organisms are unicellular.
Near-surface layers of rock may contain blue-green algae but most energy comes from chemical synthesis of minerals.
In deeper rock layers microbes are exposed to high pressures and temperatures.