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
Trace gas the major greenhouse gases are water, carbon dioxide, methane, nitrous oxide, ozone, and CFCs. These gases can absorb infrared radiation from the Earth's surface as it passes through the atmosphere. The most important greenhouse gas is water vapor because it can trap about 80 percent of outgoing IR radiation. The second most important greenhouse gas, and the most important one affected by man-made sources into the atmosphere, is carbon dioxide. The reason for why greenhouse gases can absorb infrared radiation is their molecular structure. For example, carbon dioxide has two basic modes of vibration that create a strong dipole-moment, which