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Chapter 9

GEOG 109 Chapter Notes - Chapter 9: Tropopause, Photodissociation, Protoplanetary Disk

Geography and Environmental Planning
Course Code
GEOG 109

of 2
Blessing Onyewuchi
Chapter 9: Atmosphere of Terrestrial Planets
9.1 The Gain and Loses of Atmospheres
-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
-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
-secondary atmosphere: volcanism and impacts-> during the planetary accretion process,
minerals containing water carbon dioxide and other volatile matter collected in the interiors of
the terrestrial planets..Later as the interiors heated up the higher temperatures released these
gases from the minerals that had held them. 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
9.2 Evolution of Secondary Atmospheres
-A planets mass affects its atmosphere
-Carbon dioxide was the principal secondary atmosphere component in Venus and mars
-atmospheric greenhouse effect: traps solar radiation
-molecules such as water vapor and carbon dioxide that transmit visible radiation but absorb IR
radiation are called greenhouse molecules
-greenhouse molecules in a planets atmosphere will cause its surface temperature to rise
9.3 Earths Atmosphere
-2 principal gases that make up Earths atmosphere are nitrogen and oxygen
-Ozone is formed when UV light from the Sun breaks molecular oxygen into its individual atoms
(O) in a process called photodissociation
-Earths atmosphere is layered like an onion
-lowest layer (troposphere), tropopause, stratosphere, mesosphere, thermosphere, ionosphere,
What creates weather? Local weather is caused by winds and convection
9.4 Venus has a hot dense atmosphere
-Mars has a cold, thin atmosphere