History of Life

1. History of Life Chapter 14

2. Aristotle (384 –322 BC) Proposed the theory of spontaneous generation Also called abiogenesis Idea that living things can arise from nonliving matter Idea lasted almost 2000 years

3. Spontaneous Generation • For centuries, people based their beliefs on their interpretations of what they saw going on in the world around them without testing their ideas • They didn’t use the scientific method to arrive at answers to their questions • Their conclusions were based on untested observations

4. Example #1 • Observation: Every year in the spring, the Nile River flooded areas of Egypt along the river, leaving behind nutrient-rich mud that enabled the people to grow that year’s crop of food. However, along with the muddy soil, large numbers of frogs appeared that weren’t around in drier times • Conclusion:muddy soil gave rise to the frogs

5. Example #2 • Observation:Since there were no refrigerators, the mandatory, daily trip to the butcher shop, especially in summer, meant battling the flies around the carcasses. Typically, carcasses were “hung by their heels,” and customers selected which chunk the butcher would carve off for them. • Conclusion:the rotting meat that had been hanging in the sun all day was the source of the flies.

6. Spontaneous GenerationRecipes • Recipe for bees: • Kill a young bull, and bury it in an upright position so that its horns protrude from the ground. After a month, a swarm of bees will fly out of the corpse.

7. Disproving Spontaneous Generation

8. In 1668, Francesco Redi, an Italian physician, did an experiment with flies and wide-mouth jars containing meat • His hypothesiswas that rotten meat does not turn into flies Francesco Redi (1668)

9. Redi’s Experiment • A third jar was sealed and thus not exposed to either air or flies • Results: No flies One Jar contained meat exposed to both air and flies Results:Found maggots that hatched into flies A second jar contained meat in a container wrapped in a fine cloth so that the meat was exposed to air, but not flies Results: No flies

10. Results of Redi’s Experiments • The results of this experiment disproved the idea of spontaneous generation for larger organisms • People still thought microscopic organisms like algae or bacteria could arise that way. • ****Wide-mouth jars each containing a piece of meat were subjected to several variations of “openness” while all other variables were kept the same.

11. Disproving Spontaneous Generation of Microbes

12. Conducted an experiment where he boiled soups for almost an hour and sealed containers by melting the slender necks closed. • His hypothesis was that microorganisms formed not from the air but from other microorganisms Lazzaro Spallanzani (1765)

13. Spallanzani’s experiment • Experimental group – Boiled broth for several hours to kill all the microorganisms in the broth and inside of the container • Then: melted the necks of the containers shut while broth still hot • Broth would remain microbe free. However, when the flask was opened growth would occur • Control group – Boiled broth for several hours to kill all the microorganisms in the broth and inside of the container • Broth became contaminated and cloudy

14. Results of Spallanzani’s experiment • Conclusion: Boiled broth became contaminated only when microorganisms from the air entered the flask • Critics said Spallanzani heated the flasks too long, destroying the “vital force” found in the air inside them. • Air lacking “vital force”, they claimed, could not generate life. Therefore, spontaneous generation was kept alive for another century

15. Warm up question • 1. What does the 1st sealed flask contain? • 2.How does the broth change during the experiment? 1 yr passes, broth remains clear One day passes, broth becomes cloudy Broth is boiled Flask is opened

16. Pasteur put broth into several special S-shaped flasks • Hypothesis:Microbes come from cells of organisms on dust particles in the air; not the air itself. Louis Pasteur (1822-1895)

17. Pasteur’s Experiment • Pasture filled beakers with broth and curved the neck to create S-shaped Flasks that trapped any dust particles containing bacteria • After boiling the broth to kill any microbes present the broth remained uncontaminated indefinitely • If the neck was broken the broth became cloudy and contaminated with a day

18. The Theory of Biogenesis • Pasteur’s S-shaped flask kept microbes out but let air in. • Proved microbes only come from other microbes (life from life) - biogenesis

19. Activity- Earth’s timeline 1st flowering plants 1st Life Multicellular organisms Invasion of Land 1st Eukaryotes 1st Photosynthetic bacteria Extinction of Dinosaurs Last of the Glaciers recede from temperate zones Homo Sapiens appeared Continents appear essentially as they do today 1st Aerobic Bacteria • Materials: 1 ruler, 1 sheet of paper, colored pencils or markers • Instructions: • Draw a horizontal line that will represent the timeline of Earth’s History • The far left side starts at the current estimated formation of the Earth, mark 4.6 Billion Years ago • The far right side represents present day • Place these key events where your group estimates they happened and include a date, ex 2.6Bya, 100Mya, 14,000 yrs • Work in groups of 4 • Do not talk to other groups

20. 800 Mya Multicellular Organisms 250 Mya 1st flowering Plants 3 Bya 1st Photosynthetic bacteria 3.8 Bya 1st Life 20 Mya Continents appear as they do today 15,000 Yrs Last Glaciers Recede 4Bya 3Bya 2Bya 1Bya 2.1 Bya 1st Aerobic Bacteria 160,000 yrs Homo sapiens 4.6 Bya Formation of Earth 65 Mya Extinction of Dinos 1.6 Bya 1st Eukaryotes 300 Mya Invasion of land