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Origin of the Earth's Atmosphere

Origin of the Earth's Atmosphere. 1. Hot . Why? - Primordial heat, collisions and compression during accretion, decay of short-lived radioactive elements .

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Origin of the Earth's Atmosphere

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  1. Origin of the Earth's Atmosphere 1. Hot Why? - Primordial heat, collisions and compression during accretion, decay of short-lived radioactive elements Consequences - Constant volcanism, surface temperature too high for liquid water or life as we know it, molten surface or thin, unstable basaltic crust. 2. Atmosphere - early atmosphere probably completely different in composition (H2, He) 3. Cooling Primordial heat dissipated to space Condensationof water (rain), accumulation of surface water. Accumulationof new atmosphere due to volcanic out gassing

  2. Evolution of the Atmosphere Atmosphere - Envelope of gases that surrounds the Earth. Used by life as a reservoir of chemical compounds used in living systems. Atmosphere has no outer boundary, just fades into space. Dense part of atmosphere (97% of mass) lies within 30 km of the Earth (so about same thickness as continental crust).

  3. First Atmosphere 1. Composition - Probably H2, He 2. These gases are relatively rare on Earth compared to other places in the universe and were probably lost to space early in Earth's history because a.Earth's gravity is not strong enough to hold lighter gases b.Earth still did not have a differentiated core (solid inner/liquid outer core) which creates Earth's magnetic field (magnetosphere = Van Allen Belt) which deflects solar winds. 3. Once the core differentiated the heavier gases could be retained

  4. Second Atmosphere Produced by volcanic out gassing No free O2 at this time (not found in volcanic gases). Gases produced were probably similar to those created by modern volcanoes (H2O, CO2, SO2, CO, S2, Cl2, N2, H2) and NH3 (ammonia) and CH4 (methane)

  5. Addition of O2 to the Atmosphere Today, the atmosphere is ~21% free oxygen. How did oxygen reach these levels in the atmosphere? Oxygen Production a. Photochemicaldissociation - breakup of water molecules by ultraviolet b. Photosynthesis- CO2 + H2O + sunlight = organic compounds + O2 - produced by cyanobacteria, and eventually higher plants - supplied the rest of O2 to atmosphere.

  6. Chemical Composition Today - Nitrogen (N2)- 78%, Oxygen (O2)- 21%, Carbon Dioxide (CO2) - 0.03 %, plus other miscellaneous gases (H2O for one).

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