ORIGINS OF LIFE

1. ORIGINS OF LIFE

2. People since the time of the ancient Greeks and Romans have tried to determine not only thecharacteristicsof living organisms, butwhere they come from!

3. 330 B.C. ARISTOTLE • Highly respected Greek philosopher • Observed that meat left out in the open would soon decay and have MAGGOTS! • Formed a hypothesis that “living maggots form from non-living meat”

4. Aristotle’s ideas became… The Theory of Spontaneous Generation “Living things come from non-living things"

5. 1600’s Jean Baptiste van Helmont • Lived almost 2,000 years after Aristotle! • Placed sweaty underwear with grain in a “closed” box and checked it regularly • After 21 days he found mice • Concluded that Spontaneous Generation was true: sweat penetrated the grain to make mice! Sweat + grain = mice!

6. 1668 Francesco Redi • Italian doctor that made the first serious attack on Spontaneous Generation • Tried to disprove Aristotle’s theory by carrying out a controlled experiment

7. “Controlled Experiment” Scientists carry out 2 simultaneous tests that are identical in every way, except for ONE FACTOR that is different (the VARIABLE) Any difference in the results of the 2 tests must be due to the VARIABLE.

8. Redi’s Experiment • Redi hypothesized that maggots come from eggs laid by flies, and not from the meat itself • He put snake meat into: (a) open jars, (b) tightly sealed jars, and (c) jars covered with cloth • Meat shriveled up in all the jars, but only the OPEN JARS got maggots; there were NO MAGGOTS in jars where the flies could not reach the meat!

9. Q: What was Redi’s experimental variable?

10. A: open jar versus covered jar

11. Q: Why did Redi use both tightly closed jars as well as cloth-covered jars in his experiment?

12. A: People at the time believed that spontaneous generation could not occur without AIR.

13. Critics eventually agreed that maggots could not spontaneously generate from meat, but thought other organisms COULD. • Support for S.G. remained strong! Summary video

14. 1860 Louis Pasteur • Well-respected French chemist • Entered a contest of the French Academy of Science to definitively prove or disprove Spontaneous Generation

15. He curved the neck of a flask into an “S” shape to allow AIR in, but not MICROBES • (people did not think there were microbes in the air, but Pasteur did) • He put chicken broth inside the flask and BOILED it

16. There was no microbial growth in the broth, even after a year! • Pasteur then tipped the flask (to allow broth to reach the curve) • Microorganisms then grew in the broth!

17. Q: Why did the microbes grow in the broth after the flask was tipped?

18. A: The broth came into contact with the dust & bacteria trapped in the curve, which contaminated the broth

19. Pasteur definitively PROVED there are microbes in the air, and definitively DISPROVED S.G.! • People still kept believing in S.G. for 20 years AFTER Pasteur’s experiment • In 1870, the Theory of Spontaneous Generation was replaced with… THE THEORY OF BIOGENESIS “Living things come from other living things” Summary video