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Chapter 26: Early Earth and the Origin of Life

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Chapter 26: Early Earth and the Origin of Life Phylogeny Traces life backward to common ancestors. How did life get started? Fossil Record Earliest - 3.5 billion ... – PowerPoint PPT presentation

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Title: Chapter 26: Early Earth and the Origin of Life


1
Chapter 26 Early Earth and the Origin of Life
2
Phylogeny
  • Traces life backward to common ancestors.
  • How did life get started?

3
Fossil Record
  • Earliest - 3.5 billion years old.
  • Earth - 4.5 billion years old.

4
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5
Prokaryotes
  • Fossil Modern

6
Bacterial Mats
7
Point
  • Life on earth started relatively soon after the
    earth was formed.

8
Chemical Evolution
  • The evolution of life by abiogenesis.

9
Steps
  • 1. Monomer Formation
  • 2. Polymer Formation
  • 3. Protobiont Formation
  • 4. Origin of Heredity

10
Primitive Earth Conditions
  • Reducing atmosphere present.
  • Simple molecules
  • Ex H2O, CH4, H2, NH3

11
Complex Molecule Formation
  • Requires energy sources
  • UV radiation
  • Radioactivity
  • Heat
  • Lightning

12
Oparin and Haldane 1920s
  • Hypothesized steps of chemical evolution from
    primitive earth conditions.

13
Miller and Urey, 1953
  • Tested Oparin and Haldanes hypothesis.
  • Experiment - to duplicate primitive earth
    conditions in the lab.

14
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15
Results
  • Organic monomers formed including Amino Acids.

16
Other Investigator's Results
  • All 20 Amino Acids
  • Sugars
  • Lipids
  • Nucleotides
  • ATP

17
Hypothesis
  • Early earth conditions could have formed monomers
    for life's origins.

18
Polymer Synthesis
  • Problem
  • Monomers dilute in concentration.
  • No enzymes for bond formation.

19
Possible Answer
  • 1. Clay
  • 2. Iron Pyrite

20
Explanation
  • Lattice to hold molecules, increasing
    concentrations.
  • Metal ions present which can act as catalysts.

21
Protobionts
  • Aggregates of abiotically produced molecules.
  • Exhibit some properties of life.
  • Ex Osmosis, Electrical Charge, Fission

22
Protobionts
23
Protobiont Formation
  • Proteinoids H2O ? microspheres
  • Liposomes H2O ? lipid membranes

24
Coacervates
  • Colloidal droplets of proteins, nucleic acids and
    sugars surround by a water shell.
  • Will form spontaneously from abiotically produced
    organic compounds.

25
Summary
  • Protobionts have membrane-like properties and are
    very similar to primitive cells.
  • Start for selection process that lead to cells?

26
Question ?
  • Where did the energy come from to run these early
    cells?

27
Answer
  • ATP.
  • Reduction of sulfur compounds.
  • Fermentation.
  • Rs and Ps developed much later.
  • Review materials in Chapter 27.

28
Genetic Information
  • DNA ? RNA ? Protein
  • Too complex for early life.
  • Other forms of genetic information?

29
RNA Hypothesis
  • RNA as early genetic information.

30
Rationale
  • RNA polymerizes easily.
  • RNA can replicate itself.
  • RNA can catalyze reactions including protein
    synthesis.

31
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32
Ribozymes
  • RNA catalysts found in modern cells.
  • e.g. ribosomes
  • Possible relic from early evolution?

33
Molecular Cooperation
  • Interaction between RNA and the proteins it made.
  • Proteins formed may serve as RNA replication
    enzymes.

34
Molecular Cooperation
  • Works best inside a membrane.
  • RNA benefits from the proteins it made.

35
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36
Selection favored
  • RNA/protein complexes inside membranes as they
    were the most likely to survive and reproduce.

37
DNA Developed later as the genetic information
  • Why? More stable than RNA

38
Alternate View
  • Life developed in Volcanic Vents.

39
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40
Volcanic Vents
  • Could easily supply the energy and chemical
    precursors for chemical evolution.
  • Most primitive life forms are the prokaryotes
    found in or near these vents.

41
Modern Earth
  • Oxidizing atmosphere.
  • Life present.
  • Prevents new abiotic formation of life.

42
Hypothesis
  • Life as a natural outcome of chemical evolution.
  • Life possible on many planets in the universe.

43
Kingdom
  • Highest Taxonomic category
  • Old system - 2 Kingdoms
  • 1. Plant
  • 2. Animal

44
5 Kingdom System
  • R.H. Whittaker - 1969
  • System most widely used today.

45
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46
Main Characteristics
  • Cell Type
  • Structure
  • Nutrition Mode

47
Monera
  • Ex Bacteria, Cyanobacteria
  • Prokaryotic

48
Protista
  • Ex Amoeba, Paramecium
  • Eukaryotic
  • Unicellular or Colonial
  • Heterotrophic
  • Review Chapter 28

49
Fungi
  • Ex Mushrooms, Molds
  • Eukaryotic
  • Unicellular or Multicellular
  • Heterotrophic - external digestion
  • Cell wall of chitin

50
Plantae
  • Ex Flowers, Trees
  • Eukaryotic
  • Multicellular
  • Autotrophic
  • Cell wall of Cellulose/Silicon

51
Animalia
  • Ex Animals, Humans
  • Eukaryotic
  • Multicellular
  • Hetrotrophic - internal digestion
  • No cell wall

52
Other Systems
  • Multiple Kingdoms split life into as many as 8
    kingdoms. (review Chapter 28)
  • Domains a system of classification that is
    higher than kingdom.

53
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54
3 Domain System
  • Based on molecular structure for evolutionary
    relationships.
  • Prokaryotes are not all alike and should be
    recognized as two groups.
  • Gaining wider acceptance.

55
3 Domains
  • 1. Bacteria prokaryotic.
  • 2. Archaea prokaryotic, but biochemically
    similar to eukaryotic cells.
  • 3. Eucarya the traditional eukaryotic cells.

56
Summary
  • Systematics is still evaluating the evolutionary
    relationships of life on earth.
  • Be familiar with the conditions of primitive
    earth.
  • Know the steps of chemical evolution.

57
Summary
  • Recognize the 5 Kingdoms.
  • Recognize alternate systems for classification.
  • Know about Domains.
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