The Brethren Moons (or Brother Moons and Blood Moons) are the source of the Marker signals. They are believed to be the final life cycle stage of the Necromorphs. The Brethren Moons, though their origins are unknown, are a series of moon-sized creatures throughout the galaxy that consume all organic life that they encounter through the use of their Markers. The Moons consume new worlds by sending out Black Markers, which travel through space and impact planets; in the case of Earth, the Black Marker was carried inside an asteroid that struck the Yucatan Peninsula around 65 million years B.C. It is unknown if the Moons specifically target worlds that show promise for intelligent life, or, as theorized by the Unitologist leader Jacob Danik, if the Markers are actually responsible for encouraging the evolution of intelligent species.