1. Outline 17-2: Earth's Early History
Photo credit: Jackie Beckett/American Museum of Natural History
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I. Early Earth
A. The Earth is thought to be billion years old.
1. At first a fiery ball of molten rock
2. Eventually cooled & formed a rocky crust
3. Water vapor condensed to form oceans
a. Scientists think that first life evolved in these oceans
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3. II. Origins of Living Cells
A. Biogenesis does not answer the question:
1. How did life begin on Earth?
a. No one will ever know for certain how life began
b. Scientists have developed theories about the origin of life from testing scientific hypotheses about conditions on early Earth
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4. B. How basic chemicals could form
1. All elements necessary for life were apparently found on Earth from its beginnings.
a. Physical & chemical processes alone can explain the origins of ever more complex organic chemicals on our planet
b. This hypothesis has been tested & confirmed many times in laboratory experiments.
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2. Primordial soup model
a. Oparin & Haldane’s (1920s) idea:
 Earth’s early atmosphere contained ammonia, hydrogen, methane & water vapor
 Heat from volcanoes, sunlight and lightning could have caused them to form organic compounds
 Accumulated in a sea called the primordial soup
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6. 3. Miller & Urey’s Experiment (1953)
a. Tested Oparin’s hypothesis
 Put suggested gases in chamber
 Used sparks to simulate lightning
b. Results:
 Complex chemical “zoo” which included organic compounds like :
amino acids
fatty acids
hydrocarbons
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7. The First Organic Molecules
Miller and Urey’s Experiment
Mixture of gases simulating
atmosphere of early Earth
Spark simulating
lightning storms
Condensation
chamber
Water
vapor
Cold water cools chamber, causing droplets to form.
Miller and Urey produced amino acids, which are needed to make proteins, by passing sparks through a mixture of hydrogen, methane, ammonia, and water. This and other experiments suggested how simple compounds found on the early Earth could have combined to form the organic compounds needed for life.
Liquid containing amino acids and other organic
compounds
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8. 4. Reevaluating primordial soup model
a. Early atmosphere probably did NOT contain methane & ammonia. It probably contained hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, hydrogen sulfide, and water.
b. Without methane & ammonia some key biological molecules are not made.
c. So how could organic molecules form?
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5. Bubble model
a. Louis Lerman (1986) suggested key processes took place within bubbles on the ocean’s surface.
 While inside bubbles, gases get protection from UV radiation
 Reactions could take place faster inside bubbles (concentrated)
 Bubbles could later rise to surface & release organic molecules into ocean
 Energy could cause these to react & build even more complex molecules
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10. C. How complex chemicals could form
1. Amino acids could have then spontaneously linked together to form proteins
2. RNA has been found to form spontaneously in water
a. RNA could have been first self replicating molecule
b. It could also have catalyzed the first assembly line of proteins
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11. The Puzzle of Life's Origin
Proteins build cell
structures and catalyze
chemical reactions
RNA and the Origin of Life
RNA nucleotides
Simple organic
molecules
RNA helps in
protein synthesis
Abiotic “stew” of
inorganic matter
One hypothesis about the origin of life, illustrated here, suggests that RNA could have evolved before DNA. Scientists have not yet demonstrated the later stages of this process in a laboratory setting. 
RNA able to replicate itself,
synthesize proteins, and
function in information
storage
DNA functions in
information storage
and retrieval
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3. Microspheres Cells
a. Lipids have been shown to gather in water & form a bilayer sphere
b. Chains of amino acids will gather into tiny vesicles called proteinoid microspheres
c. Have selectively permeable membranes & can store & release energy
d. These vesicles could have been first step toward cells
Problem: They don’t reproduce!
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Free Oxygen
III. Oldest Fossils
A. Are microfossils of unicellular prokaryotic organisms resembling modern bacteria
B. Found in rocks 3.5 billion years old.
C. Were anaerobic organisms.
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Free Oxygen
IV. First Oxygen
A. About 2.2 billion years ago, photosynthetic bacteria began to pump oxygen into the oceans.
B. Next, oxygen gas accumulated in the atmosphere.
C. Rise of oxygen probably caused some life forms to go extinct while others took advantage of oxygen in new ways (aerobic respiration)
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Free Oxygen
V. The Endosymbiotic Theory
A. Idea that eukaryotic cells formed from a symbiosis among several different prokaryotes.
1. Ones that used oxygen evolved into mitochondria
2. Ones that could do photosynthesis evolved into chloroplasts
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16. Origin of Eukaryotic Cells
DON’T COPY!
Endosymbiotic Theory
Ancient Prokaryotes
Chloroplast
Plants and plantlike protists
Aerobic
bacteria
Photosynthetic bacteria
Nuclear envelope
evolving
Mitochondrion
Primitive Photosynthetic
Eukaryote
The endosymbiotic theory proposes that eukaryotic cells arose from living communities formed by prokaryotic organisms. Ancient prokaryotes may have entered primitive eukaryotic cells and remained there as organelles.
Animals, fungi, and
non-plantlike protists
Ancient Anaerobic
Prokaryote
Primitive Aerobic
Eukaryote
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17. Origin of Eukaryotic Cells
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Aerobic
bacteria
Ancient Prokaryotes
Nuclear envelope
evolving
The endosymbiotic theory proposes that eukaryotic cells arose from living communities formed by prokaryotic organisms. Ancient prokaryotes may have entered primitive eukaryotic cells and remained there as organelles.
Ancient Anaerobic Prokaryote
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18. Origin of Eukaryotic Cells
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Mitochondrion
Prokaryotes that use oxygen to generate energy-rich molecules of ATP evolved into mitochondria.
The endosymbiotic theory proposes that eukaryotic cells arose from living communities formed by prokaryotic organisms. Ancient prokaryotes may have entered primitive eukaryotic cells and remained there as organelles.
Primitive Aerobic Eukaryote
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19. Origin of Eukaryotic Cells
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Prokaryotes that carried out photosynthesis evolved into chloroplasts.
Chloroplast
Photosynthetic bacteria
The endosymbiotic theory proposes that eukaryotic cells arose from living communities formed by prokaryotic organisms. Ancient prokaryotes may have entered primitive eukaryotic cells and remained there as organelles.
Primitive Photosynthetic Eukaryote
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17-2
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17-2
Which of the following gases was probably NOT present in the early Earth’s atmosphere?
hydrogen cyanide
oxygen
nitrogen
carbon monoxide
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17-2
Miller and Urey's experiment was a simulation of Earth's early
volcanic activity.
formation.
atmosphere.
life.
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17-2
Proteinoid microspheres are different from cells because microspheres
have selectively permeable membranes.
do not have DNA or RNA.
have a simple means of storing and releasing energy.
separate their internal environment from the external environment.
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17-2
The hypothesis that RNA sequences appeared before DNA sequences
has some evidence in its favor but is still being tested.
has been rejected since DNA is required to make RNA.
has been proven since RNA has been made in laboratories.
has been rejected because it is illogical.
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17-2
As concentrations of oxygen rose in the ancient atmosphere of Earth, organisms began to evolve
anaerobic pathways.
plasma membranes.
metabolic pathways that used oxygen.
photosynthesis.
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