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Geog. 111 Notes 2

Geog. 111 Notes 2 - -history and structure of the...

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- history and structure of the atmosphere: -early Earth atmosphere: hydrogen, helium, methane, CO2, and ammonia are main gases -present atmosphere: nitrogen, oxygen, water vapor (highly variable) are main gases; methane (comes from rice cultivation, cattle raising) and CO2 are trace gases; over millions of years the Earth cooled, water vapor condensed into liquid and “rained down”, forming Earth’s oceans -as gases “rained down”, vast majority of CO2 got stored in the oceans and in limestone (this essentially initiated the hydrological cycle) -oxygen apparently came from blue/ green algae (single celled organisms that formed in the oceans) that photosynthesized (being in water, they were shielded from much of the UV rays that were berating the Earth at that time) -ozone layer formed by solar radiation splitting oxygen molecules, leading to the combination of atoms to form an ozone layer (this paved way for life on land) -other trace gases include CFCs (coolant, produced by humans and used primarily to make
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