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Photosynthesis
(Process that changed history)
Light energy
+ CO2 + H2O  glucose + O2
IMPORTANT POINTS:
 Example of 1st Law of Thermodynamics: (E conservation)
• Radiant energy (light)  chemical energy (glucose)
 Carbon from atmosphere locked into an
organic molecule (glucose)
Carbon – fixation! (This point covered for Test IV)
 Water molecules split  O2 gas is released!
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Evolution of the Earth’s
Atmosphere
The Continuing Story
Major Episodes in the History of Life
Millions of years ago
475
570
1,000
1,700
2,500
3,500
4,500
Major Episode
Plants and fungi colonize land
All major animal phyla established
First multicellular organisms
Oldest eukaryotic fossils
Accumulation of atmospheric 02
Oldest prokaryotic fossils
Origin of Earth
3 15.1
Visual Summary
4.5 BYA
Earth Formed
What was original atmosphere like?
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3.5 BYA
• Life appeared! (Prokaryotic)
• Q: Did these organisms need oxygen to
live?
• Then some “New guys” appeared……
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Cyanobacteria or “blue-green algae”
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2.5 BYA
• Significant build up of oxygen gas in
Earth’s atmosphere
(Due to photosynthesis!)
• Many original inhabitants die due to this
“Pollution Crises!”
• Some organisms adapt & use O2 to release
stored energy of food.
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1.7 – 1.5 BYA
• The Rise of Eukaryotes!
• First: Protists 
plants, animals, & fungi
• 1.0 BYA
Life experiments with multi-cellularity!
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~ ½ BYA
(570mya)
• CAMBRIAN EXPLOSION!
• All major animal phyla established!
( 470 mya)
 Terrestrial life appears
(First Fungi & plants, then animals)
 What was necessary for terrestrial life?
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OZONE!
• O2 + O2 + O2 = 2 O3
• Why is Ozone so important?
*
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