GEO 125

Physical Geography

Origins of the Atmosphere

• Billions of meteors in orbit around the sun
• Collision of the meteorites form the protoplanet earth approximately 4.5 billion years ago
• Meteors contain the essential elements for life on the planet especially water
• The earth heats up due to the continued impacts of meteors on the earth's surface and the decay of radioactive material in the earth's interior
• The occurrence of volcanic eruptions release gases into the atmosphere including carbon dioxide and water in a process known as degassing
• The earth's paleoatmosphere is very similar to the modern atmosphere of Venus; temperatures are extremely high due to the very high levels of carbon dioxide in the atmosphere
• The earth begins to cool causing the condensation of water vapor and the formation of clouds
• As the earth continues to cool, it begins to rain and the oceans are formed.
• Life begins in the oceans approximately 3.5 billion years ago; ancient oceanic life forms were protected from the harmful effects of ultraviolet radiation because water is capable of filtering out the effects of ultraviolet radiation
• Ancient plant life in the oceans begin to utilize atmospheric carbon dioxide absorbed into the ocean in the process of photosynthesis; as a result simple organisms such as stromatolites begin to release oxygen into the ocean as a by-product of photosynthesis
• The oceans become saturated with oxygen; oxygen is released into the atmosphere and the ozone layer is formed in the stratosphere (ozone is a form of oxygen)
• The formation of the ozone layer permits plant and animal life to emerge from the oceans onto the dry land approximately 400 million years ago
• Concurrent with the release of oxygen from the oceans into the atmosphere and the formation of the ozone layer, oceanic life forms manufacture calcium carbonate shells (that eventually is turned into limestone) in a manner similar to the same process seen in modern oceanic life forms such as coral
• Reduction in atmospheric carbon dioxide leads to atmospheric cooling.
• It has been estimated that the temperature of the ancient atmosphere was at least 25 degrees higher than today
• The amount of atmospheric carbon dioxide continued to decrease and the amount of atmospheric free oxygen continued to increase.

Main Menu