14-life begins - h
TRANSCRIPT
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Life Begins
A. Biogenesis
B. Fossil Dating
C. Abiogenesis
D. Where Did Life Begin?
E. The First Life-forms
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A. Biogenesis
1. Spontaneous generation wasonce believed to be theorigin of life
2. Francesco Redi discoveredthat maggots came from
eggs (biogenesis)_
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3. Lazzaro Spallanzani
a. showed that when air waskept out, microbes didnot grow
b. Some believed that the
air contained avital force_
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4. Louis Pasteur - showed thatair did not possess a vitalforce_
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B. Fossil Dating
1. Radioactive dating has beenused to find exact ages offossils
a. an isotopes half-life isthe time it takes for
half of the isotope todecay
b. Earth is shown to be 4.6billion years old
c. Formed as debris thatcircled the suncoalesced_Click
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1. Alexander Oparin BelievedEarths primitive atmospherecontained NH3, H2, H2O, andCH4
a. As Earth cooled, lightning
and ultraviolet radiationformed organiccompounds thatprecipitated into aPrimordial Soup
b. coacervates (small lipid-
like membranes) mayhave formed_
C.Abiogenesis
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2. Stanley Miller and HaroldUrey set up an experimentto test Oparins theory
a. formation of small organicmolecules including
amino acidsb. microspheres (small
protein membranes) maythen have formed asamino acids joined_
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3. Space Debris
a. organic molecules mayhave formed elsewherein the universe
b. these compounds may
have arrived onmeteors_
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D. Where Did Life Begin?
1. Many scientists believe thatdeep-sea hydrothermalvents may have been thelocation of lifes origin
a. CO2 in the atmosphere
may have interferedwith Miller-Ureyresults_
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1. RNA was probably the firstnucleic hereditary material
a. RNA molecules canself-replicate
b. RNA is necessary to
catalyze proteinsynthesis
c. Ribozymes RNAenzymes_
E. The First Life-forms
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2. Prokaryotes
a. Early prokaryotes wouldhave been anaerobicchemoheterotrophs
b. As organic material ran low,
anaerobicchemoautotrophs wouldhave followed
c. Photoautotrophs would havecome next(cyanobacteria)
d. Aerobic chemoheterotrophswould have followed_
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3. Eukaryotes
a. the inner folding of themembrane- nucleus & ER
b. engulfing of prokaryotes-mitochondrion
& chloroplast(endosymbiosis)_
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THEEND