Atmosphere of Earth primarily hydrogen. There were probably simple hydrides such as those now found in the gas giants (Jupiter and Saturn), notably water vapor, methane and ammonia. Outgassing from volcanism, supplemented by gases produced during the late heavy bombardment of Earth by huge asteroids, produced the next atmosphere, consisting largely of nitrogen plus carbon dioxide and inert gases. A major part of carbon-dioxide emissions dissolved in water and reacted with metals such as calcium and magnesium during weathering of crustal rocks to form carbonates that were deposited as sediments. Water-related sediments have been found that date from as early as 3.8 billion
Messier 78 two B-type stars, and , are responsible for making the cloud of dust in M78 visible by reflecting their light. The M78 cloud contains a cluster of stars that is visible in the infrared. Due to gravity, the molecular gas in the nebula has fragmented into a heirarchy of clumps, the denser cores of which about to form stars with masses of up to . About 45 variable stars of the "T Tauri" type, young stars still in the process of formation as well as some 17 Herbig–Haro objects are known in M78. Messier 78 Messier 78 or M 78,