1 origin of life copyright cmassengale. 2 aristotle (384 –322 bc) proposed the theory of...

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Origin of LifeOrigin of Life

copyright cmassengale

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Aristotle (384 –322 BC)Aristotle (384 –322 BC)

Proposed the theory of Proposed the theory of spontaneous generationspontaneous generationAlso called Also called abiogenesisabiogenesisIdea that Idea that living things can living things can arise from nonlivingarise from nonliving matter matterIdea lasted almost Idea lasted almost 2000 2000 yearsyears


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Spontaneous GenerationSpontaneous Generation

For centuriesFor centuries, , people basedpeople based their their beliefsbeliefs onon their their interpretations of interpretations of what they what they sawsaw going on in the world going on in the world around them without testing around them without testing their ideastheir ideas They They didn’t use the scientific didn’t use the scientific methodmethod to arrive at answers to to arrive at answers to their questionstheir questionsTheir conclusions were based on Their conclusions were based on untested observationsuntested observations


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Examples of Examples of Spontaneous Spontaneous GenerationGeneration


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Example #1Example #1

Observation:Observation: Every year in the Every year in the spring, the spring, the Nile River floodedNile River flooded areas of Egypt along the river, areas of Egypt along the river, leaving behind nutrient-rich leaving behind nutrient-rich mud that enabled the people mud that enabled the people to grow that year’s crop of to grow that year’s crop of food. However, along with the food. However, along with the muddy soil, muddy soil, large numbers of large numbers of frogsfrogs appeared that weren’t appeared that weren’t around in drier timesaround in drier times


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Example #1Example #1Conclusion:Conclusion: It was It was perfectly obvious to people perfectly obvious to people back then that back then that muddy soil muddy soil gave rise to the frogsgave rise to the frogs


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Observation:Observation: In many parts of In many parts of Europe, medieval farmers Europe, medieval farmers stored stored grain in barnsgrain in barns with with thatched roofs (like thatched roofs (like Shakespeare’s house). As a Shakespeare’s house). As a roof aged, it was not roof aged, it was not uncommon for it to start uncommon for it to start leaking. This could lead to leaking. This could lead to spoiled or moldy grainspoiled or moldy grain, and of , and of course there were course there were lots of mice lots of mice aroundaround..


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Conclusion: It was obvious It was obvious to them that the to them that the mice mice came from the moldy came from the moldy grain.grain.


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Example #3Example #3Observation:Observation: In the cities In the cities centuries ago, there were no centuries ago, there were no sewers, no garbage trucks, no sewers, no garbage trucks, no electricity, and no refrigeration. electricity, and no refrigeration. Sewage flowed down the Sewage flowed down the streets, and chamber pots and streets, and chamber pots and left over foodleft over food were thrown out were thrown out into the streets each morning. into the streets each morning. Many cities also had major Many cities also had major rat rat problemsproblems and a disease called and a disease called Bubonic plagueBubonic plague..


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Conclusion:Conclusion: Obviously, all Obviously, all the the sewage and garbage sewage and garbage turned into the ratsturned into the rats.


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Observation:Observation: Since there were Since there were no refrigerators, the no refrigerators, the mandatory, daily trip to the mandatory, daily trip to the butcher shop, especially in butcher shop, especially in summer, summer, meant battling the meant battling the flies around the carcassesflies around the carcasses. . Typically, carcasses were Typically, carcasses were “hung by their heels,” and “hung by their heels,” and customers selected which customers selected which chunk the butcher would carve chunk the butcher would carve off for them. off for them.


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Conclusion: Obviously, the Obviously, the rotting meatrotting meat that had been that had been hanging in the sun all day hanging in the sun all day was the was the source of the fliessource of the flies. .


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Abiogenesis RecipesAbiogenesis Recipes

Recipe for bees:Recipe for bees:

Kill a young bullKill a young bull, and , and bury itbury it in an upright in an upright position so that its position so that its horns protrude from the horns protrude from the groundground. After a month, a . After a month, a swarm of bees will fly swarm of bees will fly out of the corpse. out of the corpse.


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Abiogenesis RecipesAbiogenesis Recipes

Recipe for mice:Recipe for mice:

Place a Place a dirty shirtdirty shirt or some rags or some rags in an in an open pot or barrelopen pot or barrel containing a containing a few grains of few grains of wheatwheat or some wheat bran, and or some wheat bran, and in in 21 days21 days, mice will appear. , mice will appear. There will be adult males and There will be adult males and females present, and they will females present, and they will be capable of mating and be capable of mating and reproducing more mice.reproducing more mice.


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Disproving Disproving Spontaneous Spontaneous GenerationGeneration


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Francesco Redi (1668)Francesco Redi (1668)

In 1668, Francesco In 1668, Francesco RediRedi, an , an Italian physician, did an Italian physician, did an experiment with experiment with fliesflies and and wide-mouth jars containing wide-mouth jars containing meatmeat


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Redi’s ExperimentRedi’s Experiment

Redi used Redi used open & closed open & closed flasksflasks which which contained contained meatmeat.. His His hypothesishypothesis was that was that rotten meat does not turn rotten meat does not turn into flies.into flies. He He observedobserved these flasksthese flasks to see in which one(s) to see in which one(s) maggots would develop.maggots would develop.


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Redi’s FindingsRedi’s FindingsHe found that if a flask was He found that if a flask was closedclosed with a lid so with a lid so adult adult flies could not get in, no flies could not get in, no maggotsmaggots developed on the developed on the rotting meat within.rotting meat within. In a flask In a flask without a lidwithout a lid, , maggots soon were seenmaggots soon were seen in in the meat because adult flies the meat because adult flies had laid eggs and more had laid eggs and more adult flies soon appeared.adult flies soon appeared.


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Redi’s (1626-1697) Experiments

Evidence against spontaneous Evidence against spontaneous generation:generation:

1. 1. Unsealed Unsealed – maggots on meat– maggots on meat2. 2. SealedSealed – no maggots on meat – no maggots on meat3. 3. GauzeGauze – few maggots on gauze, none on – few maggots on gauze, none on

meatmeat


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Results of Redi’s ExperimentsResults of Redi’s Experiments

The results of this The results of this experiment experiment disproved the disproved the idea of spontaneous idea of spontaneous generation for larger generation for larger organisms,organisms, but people still but people still thought microscopic thought microscopic organisms like algae or organisms like algae or bacteria could arise that bacteria could arise that way.way.


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Francesco RediFrancesco Redi


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Did Redi Use the Did Redi Use the Scientific Scientific Method?Method?


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The Scientific MethodThe Scientific MethodObservationObservation

HypothesisHypothesis

ExperimentExperiment

Accept, Reject, or Modify hypothesisAccept, Reject, or Modify hypothesis


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Step 1 - ObservationStep 1 - Observation

There were flies around There were flies around meat carcasses at the meat carcasses at the Butcher shop.Butcher shop.

Where do the flies come Where do the flies come from?from?

Does rotting meat turn Does rotting meat turn into or produce rotting into or produce rotting flies?flies?


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Step 2 - HypothesisStep 2 - Hypothesis

Rotten meat does not Rotten meat does not turn into flies. turn into flies. Only flies Only flies can make more flies.can make more flies.


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Step 3 - TestingStep 3 - Testing

Wide-mouth jarsWide-mouth jars each containing a piece each containing a piece of meat were subjected to several of meat were subjected to several variations of variations of “openness”“openness” while all while all other other variables were kept the same.variables were kept the same.

Control groupControl group — These jars of meat were — These jars of meat were set out set out without lidswithout lids so the meat would be so the meat would be exposed to whatever it might be in the exposed to whatever it might be in the butcher shop.butcher shop.

Experimental group(s)Experimental group(s) — One group of — One group of jars were jars were sealedsealed with lids, and another with lids, and another group of jars had gauze placed over group of jars had gauze placed over them.them.


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Step 4 - DataStep 4 - Data

Presence or absence of fliesPresence or absence of flies and maggots observed in and maggots observed in each jar was each jar was recordedrecorded..Control groupControl group – flies entered, – flies entered, laid eggs, & maggots laid eggs, & maggots emergedemergedGauze coveredGauze covered – flies on – flies on gauze, but not in jargauze, but not in jarSealed jarsSealed jars – No maggots or – No maggots or flies on the meatflies on the meat


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Step 5 - ConclusionStep 5 - Conclusion

Only flies can make more fliesOnly flies can make more flies. In the . In the uncovered jarsuncovered jars, flies entered and laid , flies entered and laid eggs on the meat. Maggots hatched from eggs on the meat. Maggots hatched from these eggs and grew into more adult these eggs and grew into more adult flies. Adult flies laid eggs on the gauze on flies. Adult flies laid eggs on the gauze on the gauze-covered jars. These eggs or the the gauze-covered jars. These eggs or the maggots from them dropped through the maggots from them dropped through the gauze onto the meat. In the gauze onto the meat. In the sealed jarssealed jars, , no flies, maggots, nor eggs could enter, no flies, maggots, nor eggs could enter, thus none were seen in those jars. thus none were seen in those jars. Maggots arose only where flies were able Maggots arose only where flies were able to lay eggs. to lay eggs. This experiment disproved This experiment disproved the idea of spontaneous generation for the idea of spontaneous generation for larger organisms.larger organisms.


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The Theory The Theory Finally ChangesFinally Changes


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How Do Microbes Arise?How Do Microbes Arise?

By By 18601860, the debate had become , the debate had become so heated that the so heated that the Paris Academy Paris Academy of Sciencesof Sciences offered a prizeoffered a prize for for any experiments that would help any experiments that would help resolve this conflictresolve this conflict

The The prize was claimed in 1864 by prize was claimed in 1864 by Louis PasteurLouis Pasteur, as he published , as he published the results of an experiment he the results of an experiment he did to disproved spontaneous did to disproved spontaneous generation in microscopic generation in microscopic organismsorganisms


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Louis Pasteur (1822-1895)Louis Pasteur (1822-1895)


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Pasteur's ProblemPasteur's Problem

Hypothesis:Hypothesis: Microbes come Microbes come from cells of organisms on from cells of organisms on dust particles in the air; not dust particles in the air; not the air itself.the air itself.

Pasteur put broth into Pasteur put broth into several special several special S-shaped S-shaped flasksflasks

Each flask was Each flask was boiled and boiled and placed at various locationsplaced at various locations


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Pasteur's Experiment - Pasteur's Experiment - Step Step 11

S-shaped FlaskS-shaped Flask

Filled withFilled with broth broth

The special shaped The special shaped was intended to was intended to trap any dust trap any dust particles containing particles containing bacteriabacteria


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FlasksFlasks boiledboiled

Microbes KilledMicrobes Killed


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Flask left at various Flask left at various locationslocations Did Did not turn cloudynot turn cloudyMicrobes not foundMicrobes not foundNotice the Notice the dustdust that that collected in the neckcollected in the neck of the flask of the flask


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Pasteur's Experimental Pasteur's Experimental ResultsResults


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Pasteur’s Pasteur’s S-shaped flask kept S-shaped flask kept microbes out but let air inmicrobes out but let air in..

Proved microbes only come from Proved microbes only come from other microbes (life from life) - other microbes (life from life) - biogenesisbiogenesis

The Theory of BiogenesisThe Theory of Biogenesis

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1 origin of life copyright cmassengale. 2 aristotle (384 –322 bc) proposed the theory of...

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