BIOL 1202 Chapter : Ch25 The History Of Life On Earth
Ch. 25: The History of Life on Earth 3/9/2014 3:29:00 AM
Early Earth
• Earth is about 4.6 billion years (BY) old
o Radiometric dating of meteorites & moon rocks
• Life arose about 3.8 BY ago
o Chemical traces in rocks 3.8 BY
o Fossil bacteria in rocks 3.5 BY
• No spontaneous generation now, but must have happened then
Conditions on Early Earth
• Atmosphere
o CO2; CH4; NH3; H2S; H2O
o No free oxygen
• Abundant energy to drive reactions
o Frequent storms w/ much lightening
o Frequent volcanic eruptions
o Frequent meteor impacts
o UV light from the sun
Testable Hypothesis explaining the Origin of Life
1. Abiotic synthesis of small organic molecules
2. Joining these molecules into polymers
3. Packaging these molecules into “protobionts”
4. The origin of self-replicating
Miller & Urey Experiments
Alternative Hypothesis
1. First organic compounds may have been synthesizes near hydrothermal
vents
2. Extraterrestrial origin
Abiotic Synthesis of Polymers
• Small organic molecules polymerize when they are concentrated on hot
sand or clay
Protobionts
• Aggregates of abiotically produced molecules surrounded by a
membrane
• Liposomes can form when lipids or whether organic molecules are
added to water
Clicker Question:
Oxygen has a ____ influence on the formation of complex organic
molecules because _______.
o Negative; it is highly reactive
