1. Outline 17-2: Earth's Early History
Photo credit: Jackie Beckett/American Museum of Natural History
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I. Early Earth
The Earth is thought to be billion years old.
At first a fiery ball of molten rock
Eventually cooled & formed a rocky crust
Water vapor condensed to form oceans
Scientists think that first life evolved in these oceans
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3. II. Origins of Living Cells
Biogenesis does not answer the question:
How did life begin on Earth?
No one will ever know for certain how life began
Scientists have developed theories about the origin of life from testing scientific hypotheses about conditions on early Earth
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How basic chemicals could form
All elements necessary for life were apparently found on Earth from its beginnings.
Physical & chemical processes alone can explain the origins of ever more complex organic chemicals on our planet
This hypothesis has been tested & confirmed many times in laboratory experiments.
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2. Primordial soup model
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)
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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
Early atmosphere probably did NOT contain methane & ammonia. It probably contained hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, hydrogen sulfide, and water.
Without methane & ammonia some key biological molecules are not made.
So how could organic molecules form?
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5. Bubble model
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
Amino acids could have then spontaneously linked together to form proteins
RNA has been found to form spontaneously in water
RNA could have been first self- replicating molecule
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
Lipids have been shown to gather in water & form a bilayer sphere
Chains of amino acids will gather into tiny vesicles called proteinoid microspheres
Have selectively permeable membranes & can store & release energy
These vesicles could have been first step toward cells
Problem: They don’t reproduce!
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III. Oldest Fossils
Are microfossils of unicellular prokaryotic organisms resembling modern bacteria
Found in rocks 3.5 billion years old.
Were anaerobic organisms.
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IV. First Oxygen
About 2.2 billion years ago, photosynthetic bacteria began to pump oxygen into the oceans.
Next, oxygen gas accumulated in the atmosphere.
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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V. The Endosymbiotic Theory
Idea that eukaryotic cells formed from a symbiosis among several different prokaryotes.
Ones that used oxygen evolved into mitochondria
Ones that could do photosynthesis evolved into chloroplasts
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16. Origin of Eukaryotic Cells
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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
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
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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20. Outline 17-3: Evolution of Life on Earth
11/30/2018

21. Prokaryotes A. Oldest fossil dated at 3. 5 bya
Prokaryotes A. Oldest fossil dated at 3.5 bya (billions of years ago) B. These were anaerobic prokaryotes C. Later, 2.2 bya, came cyanobacteria, photosynthetic bacteria. 1. They produced the first oxygen for the planet. a. Today 21% of atmosphere is oxygen D. Two types of prokaryotes: 1. Archaebacteria 2. Eubacteria

22. II. First Eukaryotes formed A. Oldest eukaryote fossils dated at. 1
II. First Eukaryotes formed A. Oldest eukaryote fossils dated at bya B. These have a nucleus & internal membranes C. Probably occurred partially by the process of endosymbiosis

23. Multicellularity Evolved A. 6 kingdoms, or groups, of life: 1
Multicellularity Evolved A. 6 kingdoms, or groups, of life: Eubacteria Archaebacteria 3. Protista 4. Fungi 5. Plantae 6. Animalia B. Half of biomass on earth is unicellular Limitations: a. No specialization occurs

24. C. Multicellularity probably evolved. more than once 1
C. Multicellularity probably evolved more than once Oldest multicellular organisms date to 700 mya. 2. Multicellular protists are red, green & brown algae (kelp=seaweed) 3. Fungi, plants & animals all evolved from different protists. 4. Most groups of organisms alive today seemed to have evolved during the Cambrian Explosion (~ mya)

25. IV. Mass extinctions: Death of many. organisms at once. A
IV. Mass extinctions: Death of many organisms at once A. Happened repeatedly during Earth’s history: 1. End of PreCambrian (540 mya) 2. End of Paleozoic (245 mya) 3. End of Mesozoic (65 mya)

26. Causes of mass extinctions. Meteorite impact theory
Causes of mass extinctions? Meteorite impact theory for end of Mesozoic Era

27. V. Evolution of the Ozone Layer. A. Sun provides light as well as
V. Evolution of the Ozone Layer A. Sun provides light as well as dangerous ultraviolet radiation B. What helped life leave the oceans? 1. Ozone Layer a. Cyanobacteria produced O b. Sun hits O2 & creates O (ozone) c. Ozone layer blocks UV radiation

28. Ozone Layer

29. VI. First Land Creatures. A. First creatures needed to live on
VI. First Land Creatures A. First creatures needed to live on bare rock (no soil yet) B. Fungi & lichens probably started out on land first. C. Photosynthetic plants came later

30. VII. First Land Animals. A. By 330 mya there were extensive
VII. First Land Animals A. By 330 mya there were extensive forests on land B. Provided ample food for animals C. First land animals were the arthropods 1. Characteristics: a. hard exoskeleton & jointed legs 2. Examples: a. Crustaceans (lobsters, crabs) b. Insects (most abundant animals today) c. Arachnids (spiders, scorpions)

31. VIII. Vertebrates. A. Animals with backbones. B
VIII. Vertebrates A. Animals with backbones B. Come in five major groups (Classes): Fishes a. Evolved by ~ 500 mya b. First were small jawless fishes c. Then came jawed fishes ( mya)

32. 2. Amphibians. a. Evolved by ~370 mya. b. First vertebrates on land. c
2. Amphibians a. Evolved by ~370 mya b. First vertebrates on land c. Smooth skinned; need to live near water d. Adaptations: Lungs, limbs evolved from fins e. Examples: Frogs, toads, salamanders

33. 3. Reptiles. a. Evolved by ~350 mya. b. Adaptations:
3. Reptiles a. Evolved by ~350 mya b. Adaptations: Waterproof skin & waterproof eggs allowed them to live in dry climates c. Examples: Snakes, lizards, turtles, crocodiles & dinosaurs

34. 4. Mammals. a. Evolved by ~220 mya. b
4. Mammals a. Evolved by ~220 mya b. Minor group at first; expanded after extinction of dinosaurs c. Adaptations: Hair, warm-blooded, mammary glands to feed young milk d. Examples: Rodents, primates, felids (cats), canids (dogs), etc.

35. 5. Birds a. Evolved by ~150 mya probably from branch of the dinosaurs b. Archeaopteryx – fossil of earliest bird. Shows reptilian & bird characteristics. c. Adaptations: Warm-blooded, feathers, hard- shelled eggs d. Examples: Ostrich, kiwi, seagulls, eagles, mockingbirds, hummingbirds