Download - Evolution of the Atmosphere
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Evolution of the Atmosphere
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Evolution of our atmosphere
• Original Atmosphere of Hydrogen (H) and Helium (He) lost.
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Secondary atmosphere develops
• planetesimal collisions – released volatiles
trapped in grains
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Early Atmosphere
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VaporMethane (CH4) and Sulfur
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Volcanic outgassing
• Carbon dioxide (CO2)
• Sulfur oxides• Water vapor
• Methane (CH4 )
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Two keys to the evolution of planetary atmospheres:
• Fate of the water vapor (gaseous, liquid, solid)
• Fate of the Carbon Dioxide (stays in atmosphere vs. dissolves in liquid water)
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Condensation of water vapor is crucial
• On this planet it was too cold for water vapor to condense. Hence the atmosphere is all Carbon Dioxide
• On this planet it was too hot for water vapor to condense. Hence the atmosphere is all Carbon Dioxide
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On this planet it was just right. The carbon dioxide content of the earth's atmosphere is now all locked
up in rocks.
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Precipitation…cools down the planet…water now as a liquid
• Condensation of water vapor produced the earth's oceans– sweeping out the
carbon dioxide and locking it up into rocks
– our atmosphere was mostly nitrogen.
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Primitive Oceans born
• CO2 + H2O (liquid) = H2CO3 = Acid rain
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Early Earth
• The freshly formed Earth was a pretty rough place,
As comets and meteors slammed in from space.
We'd choke on the gases of that atmosphere,
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Other types of rocks formed
• H2CO3 + CaMg (CO3)2 - dolomites
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Composition of our atmosphere
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What about the nitrogen?
• N2 chemically inert, so it stays in the atmosphere
• N2 cycle develops later
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Early Earth-Moon System
• The moon was closer to the Earth
• It exerted a much stronger gravitational pull on the oceans
• Contributed to the mixing of the substances present in the primitive oceans
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The evolution of Earth's oxygen atmosphere
• 4 billion years ago the earliest oxygen producing (photosynthesizing) organism occurred.
• With the presence of these organisms there was excess oxygen being formed.
• Eventually, oxygen built up in the atmosphere but this took millions of years.
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What about the oxygen?• Microscopic Mojave Desert
– plants growing on the underside of translucent quartz pebbles
• endure both chilly and near-boiling temperatures
• scavenge nitrogen from the air, and utilize the equivalent of nighttime moonlight levels for photosynthesis.
– model for how plants first colonized land
– how they might have evolved on Mars
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First oxygen producing organismsStromatolites
• Archaean era• 3.5 billion years old• Microscopic• Need only
– Nitrogen &– Carbon Dioxide
• Photosynthetic
(give off oxygen)
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Archaean Era
Stromatolites(microscopic bacteria)on the rocks
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Green sulfur bacteria
• Their environment must be oxygen-free
• need light to grow• They engage in
photosynthesis,
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Black smokers
• hydrothermal vent found on the ocean floor
• Generally hundreds of meters wide
• formed when superheated water from below the Earth's crust comes through the ocean floor
• Rich in dissolved minerals from the crust, most notably sulfides,
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Black smokers
• The temperature of the water they vent can reach 400 °C, but does not boil due to the high pressure it is under at that depth
• The water is also extremely acidic, often having a pH value as low as 2.8 — approximately that of vinegar.
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