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
Atmosphere of Mars freezing point of water. With the higher temperature, running water could have carved out the many channels and outflow valleys that are common on the planet. It also might have gathered to form lakes and maybe an ocean. Some researchers have suggested that the atmosphere of Mars may have been many times as thick as the present one of Earth; however, research published in fall 2015 advanced the idea that perhaps the early Martian atmosphere was not as thick as previously thought. Currently, the atmosphere is very thin. For many years, it was assumed that as with Earth, most of