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
Flash-gas (petroleum) to its combustion. As of 2009, energy-related CO emissions made up more than 80% of total U.S. greenhouse gas emissions. Flare and flash gas both contain GHGs and therefore contribute to their release into the atmosphere, estimates of their emission levels during petroleum production vary due to largely unmeasured release of flash gas and other forms of fugitive emissions. One study estimated a 40% increase in the atmospheric concentration of the GHG carbon dioxide (CO) is due directly to human activities since 1750. GHGs other than CO which are produced during petroleum operations are also a concern to the environment.