2. Where and how did life originate?
The Origin of Life
Where and how did life originate?

3. Spontaneous Generation
The mistaken idea that life arises from non-life
Examples:
At one time, people thought that mice could be created by placing damp hay and corn in a dark corner and that mud could give rise to worms

4. *The results failed to convince most people until the mid 1800’s!
Early Experiments
Francesco Redi (1668)
Common Belief: maggots (fly larva) arise spontaneously from rotting meat
Redi’s Hypothesis – flies, not meat, produced other flies
*The results failed to convince most people until the mid 1800’s!

5. Theory of Biogenesis
Only living organisms can produce other living organisms
Louis Pasteur (1800’s)
Designed an experiment to show that biogenesis was true even for microorganisms
(He also developed a vaccine against rabies)

6. *Experiment showed that microorganisms do not appear spontaneously.
Pasteur’s Experiment
Used a sterile nutrient broth that supports growth of microorganisms
*Experiment showed that microorganisms do not appear spontaneously.
Nutrient Broth – a liquid used to grow microorganisms. Currently used to test certain foods and dairy products for salmonella.

7. If life can only arise from life, how did the first life form appear?
A series of chemical events in which complex organic molecules (amino acids) were generated from simpler ones

8. Modern Theories for the Evolution of the 1st Organisms
Organic Molecule Hypothesis
Miller-Urey Experiment
Early Cell Structure Hypothesis
Endosymbiosis Theory

9. Organic Molecule Hypothesis
Simple organic molecules (amino acids) can be made from inorganic compounds
Early Earth’s Conditions:
Atmosphere = ammonia, water vapor, hydrogen gas and methane (NO OXYGEN)
Due to temps above boiling point, any liquid water would be evaporated right away.
Earth cooled, water vapor condensed to form water (lakes & seas)
Over time, lightning and UV light stimulated complex reactions to create proteins (building blocks of life)

10. Miller-Urey Experiment (1953)
*In a lab setting, they were able to simulate Earth’s early conditions, zap it with electricity and produce amino acids

11. Early Cell Structure Hypothesis
First cells = prokaryotes (anaerobic)
Why? They are Unicellular, smaller than Eukaryotes and don’t contain a defined nucleus or other organelles.
Evidence: Currently live in extreme environments
Examples: hot springs of Yellowstone or Hydrothermal Vents whose conditions are similar to early Earth

12. Endosymbiosis Theory
Prokaryotic cells were involved in the evolution of eukaryotic cells
Prokaryotes may have lived inside of Eukaryotes and become organelles such a chloroplasts and mitochondria
Led to the evolution of photosynthetic organisms

13. Important:
Oxygen became abundant AFTER the first life forms developed, NOT as a condition that allowed them to develop.
Bacteria = 1st organisms
After Earth cooled down, liquid water became abundant