1. Theories on the Origin of Life

2. 4 theories:
Spontaneous generation – life can come from nonliving things.
Biogenesis – life only comes from other living things
Cosmogenesis – life on Earth came from another part of our solar system or galaxy
Meteorites contain organic compounds
Conditions necessary for life may have existed on other planets or moons
4. Special creation – all religious beliefs

3. Scientists who have contributed to the theory of Biogenesis

4. 1668-Francesco Redi
Observed flies land on meat that later develops maggots.
Hypothesis: Maggots come from flies
Experiment
control - jars with meat covered
experimental – jars with meat open
Results: open jar had flies and maggots
Conclusion: maggots come from flies

5. First scientist to use a control group
Critics said there were no maggots in the closed jar because there was no air!
Redi redesigned his experiment and covered the jar with netting.
Result: Flies and maggots were on the netting, not in the jar. His hypothesis was correct!
First scientist to use a control group

6. 1668 -Redi

7. Critics said “no air “– no redesign
1700’s - Spallanzani
Hypothesis: microbes do not come from broth Experiment:
Flask with boiled gravy left open – microbes grew
Flask with boiled gravy sealed – no growth
Critics said “no air “– no redesign

9. Critics said “bad broth” Persevered and proved his point!
Pasteur
Redesigned Spallanzani’s experiment using a swan-necked flask
Flask was left open - no growth
Critics said “bad broth”
Pasteur broke off the neck and growth began
Persevered and proved his point!

10. Pasteur’s swan-necked flask: