A&O 2 - Lecture 2.1

A&O 2 - Lecture 2.1 - ! Protects non-aquatic life...

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1 Atmospheric Evolution • Primordial Atmosphere • Secondary Atmosphere • Evolution of Life vs. the Atmos. ! Pre-Photosynthetic Microbial Life ! Oxygenation of the Atmosphere • Atmospheric Catastrophes 2 Primordial Atmosphere • Condensation of the Interstellar Medium ! Hydrogen (H 2 ) + Helium (He) gases + dusts • Planetary heat drove off most of this light atmosphere out into space 3 Secondary Atmosphere • Formed by Planetary Outgassing ! Water vapor (H 2 O) + Carbon dioxide (CO 2 ) + SO 2 + N 2 + … • Planet cools over time ! Atmospheric water vapor condenses into oceans. . .important for evolution of life 4 Oxygenation of Earth’s Atmosphere • Chemical Era (no life; “pre-biotic”) • Anaerobic microbes (3.5 BYA) ! Preferred the lack of oxygen • Photosynthesizing organisms ! Cyanobacteria: Green Plant Photosynthesis takes in CO 2 and gives off O 2 as waste • Oxygenation of environment kills off anaerobes—pollution! But…
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5 • Ozone Layer forms from oxygen
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Unformatted text preview: ! Protects non-aquatic life from sunlight Aerobes evolve (2 BYA) ! Aerobes use O 2 , give off CO 2 ! Developed mutualistic relationship with green plants to maintain steady-state atmospheric O 2 content UV O 2 + UV ! ! O 3 6 Pre-biotic (3.5 to 5 BYA) ! Outgassed by Earths surface ! Chemical reactions involving ammonia (NH 3 ) 3.2 BYA and later ! Denitrification: organic compounds react with nitrate ions (NO 3 ) to release molecular nitrogen (N 2 ), nitrous oxide (N 2 O), nitric oxide (NO) Nitrogen (N 2 ) 7 Atmospheric Catastrophes Oxygenation of the atmosphere Meteor/Asteroid strike on Earth about 65 MYA ! Impact raised dust clouds, set fires that produced global clouds of smoke ! Reduced sunlight intensity reduced Earth surface temperatures; large reptiles died...
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A&O 2 - Lecture 2.1 - ! Protects non-aquatic life...

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