GEOG 109 Chapter Notes - Chapter 9: Tropopause, Photodissociation, Protoplanetary Disk
9 Dec 2014
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Only venus and earth have dense atmospheres, mars has a very low density atmospheres and the atmospheres of mercury and the moon are so sparse that they can hardly be detected. Young planets were initially enveloped by the remaining hydrogen and helium that filled the protoplanetary disk surrounding the sun, and they were able to capture some of this surrounding gas. The primary atmosphere is the gaseous envelope collected by a newly formed planet. Terrestrial planets are less massive than the giant planets and therefore have weaker gravity. Hotter molecules have higher kinetic energies than do cooler molecules and therefore move faster and more likely to escape. Volcanism then brought the various gases to the surface, where they accumulated to create the secondary atmospheres. Molecular nitrogen makes up the bulk of earths atmosphere. Carbon dioxide was the principal secondary atmosphere component in venus and mars.
