Transcript Ch 19 History of Life

1 Explain What does Miller and Urey’s experiment tell
us about the organic compounds needed for life
Predict You just read that life arose from nonlife
billions of years ago. Could life arise from nonlife
today- why
2 Review What does the endosymbiontic theory
propose
Explain According to this theory how did
mitochondria evolve
CH 19 HISTORY OF LIFE
19.3 Earth’s Early History
Early Earth
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4.6 billion years old
Started off much hotter
Evidence of high methane, carbon dioxide,
ammonia, water vapor, and hydrogen
concentrations
Went through multiple heating and cooling cycles
High heat often helps chemical reactions.
The First Organic Molecules
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1953 Miller and Urey
Tried to replicate
early Earth conditions
Produced 21 amino
acids.
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Miller and Urey’s ideas on the composition of the
early atmosphere were incorrect
New experiments based on current ideas of the
early atmosphere have produced similar results.
Microspheres
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Tiny bubble of large organic molecules
Not cells
Have selectively permeable membranes
Can store and release energy.
“RNA World” Hypothesis
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RNA evolved before DNA
Small chunks could form from simple molecules
RNA sequences help DNA replicate
RNA sequences process messenger RNA
RNA sequences catalyze chemical reactions
Some can grow and replicate on their own.
“RNA World” Hypothesis
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Early atmosphere similar to a volcano.
Production of Free Oxygen
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2.2 billion years ago photosynthetic bacteria were
common
Produced oxygen combined with iron in the oceans
Iron oxide sank to ocean floor and formed large
deposits (is the iron we mine today)
Oceans changed color from brown to blue-green.
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Oxygen gas began to accumulate in the
atmosphere
Ozone layer formed
Skies turned blue
Oxygen concentrations continued to rise.
Endosymbiotic Theory
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Prokaryotic cells entered ancestral eukaryotes and
began living inside them.
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Mitochondria evolved from endosymbiotic
prokaryotes that were able to use oxygen to
generate energy-rich ATP.
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Chloroplasts evolved from endosymbiotic
prokaryotes that had the ability to photosynthesize.
Modern Evidence
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Mitochondria and chloroplasts have ribosomes
whose size and structure closely resemble those of
bacteria
Mitochondria and chloroplasts, like bacteria,
reproduce by binary fission when cell undergoes
mitosis.
Significance of Sexual Reproduction
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Sped up evolutionary change because sexual
reproduction increases genetic variation.
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Which gas is most abundant in Earth’s
atmosphere today? What percent of that gas may
have been present in the early atmosphere
Which gas was probably most abundant in the
early atmosphere
Where did the water in today’s oceans probably
come from