Download Early Earth and the Origin of Life

Chapter 26:
Early Earth
and the Origin of Life
Phylogeny
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Traces life backward to common ancestors.
How did life get started?
Fossil Record
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Earliest - 3.5 billion years old.
Earth - 4.5 billion years old.
Prokaryotes
Fossil
Modern
Bacterial Mats
Point
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Life on earth started relatively soon after the
earth was formed.
Chemical Evolution
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The evolution of life by abiogenesis.
Steps
1. Monomer Formation
2. Polymer Formation
3. Protobiont Formation
4. Origin of Heredity
Primitive Earth Conditions
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Reducing atmosphere present.
Simple molecules
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Ex: H2O, CH4, H2, NH3
Complex Molecule Formation
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Requires energy sources:
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UV radiation
Radioactivity
Heat
Lightning
Oparin and Haldane 1920s
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Hypothesized steps of chemical evolution
from primitive earth conditions.
Miller and Urey, 1953
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Tested Oparin and Haldane’s hypothesis.
Experiment - to duplicate primitive earth
conditions in the lab.
Results
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Organic monomers formed including Amino
Acids.
Other Investigator's Results
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All 20 Amino Acids
Sugars
Lipids
Nucleotides
ATP
Hypothesis
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Early earth conditions could have formed
monomers for life's origins.
Polymer Synthesis
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Problem:
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Monomers dilute in concentration.
No enzymes for bond formation.
Possible Answer
1. Clay
2. Iron Pyrite
Explanation
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Lattice to hold molecules, increasing
concentrations.
Metal ions present which can act as catalysts.
Protobionts
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Aggregates of abiotically produced
molecules.
Exhibit some properties of life.

Ex: Osmosis, Electrical Charge, Fission
Protobionts
Protobiont Formation
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Proteinoids + H2O  microspheres
Liposomes + H2O  lipid membranes
Coacervates
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Colloidal droplets of proteins, nucleic acids
and sugars surround by a water shell.
Will form spontaneously from abiotically
produced organic compounds.
Summary
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Protobionts have membrane-like properties
and are very similar to primitive cells.
Start for selection process that lead to cells?
Question ?
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Where did the energy come from to run these
early cells?
Answer
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ATP.
Reduction of sulfur compounds.
Fermentation.
Rs and Ps developed much later.
Review materials in Chapter 27.
Genetic Information
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DNA  RNA  Protein
Too complex for early life.
Other forms of genetic information?
RNA Hypothesis
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RNA as early genetic information.
Rationale
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RNA polymerizes easily.
RNA can replicate itself.
RNA can catalyze reactions including protein
synthesis.
Ribozymes
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RNA catalysts found in modern cells.
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e.g. ribosomes
Possible relic from early evolution?
Molecular Cooperation
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Interaction between RNA and the proteins it
made.
Proteins formed may serve as RNA
replication enzymes.
Molecular Cooperation
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Works best inside a membrane.
RNA benefits from the proteins it made.
Selection favored:

RNA/protein complexes inside membranes as
they were the most likely to survive and
reproduce.
DNA Developed later as the genetic
information

Why? More stable than RNA
Alternate View
Life developed in Volcanic Vents.
Volcanic Vents
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Could easily supply the energy and chemical
precursors for chemical evolution.
Most primitive life forms are the prokaryotes
found in or near these vents.
Modern Earth
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Oxidizing atmosphere.
Life present.
Prevents new abiotic formation of life.
Hypothesis
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Life as a natural outcome of chemical
evolution.
Life possible on many planets in the universe.
Kingdom
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Highest Taxonomic category
Old system - 2 Kingdoms
1. Plant
2. Animal
5 Kingdom System
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R.H. Whittaker - 1969
System most widely used today.
Main Characteristics
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Cell Type
Structure
Nutrition Mode
Monera
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Ex: Bacteria, Cyanobacteria
Prokaryotic
Protista
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Ex: Amoeba, Paramecium
Eukaryotic
Unicellular or Colonial
Heterotrophic
Review Chapter 28
Fungi
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Ex: Mushrooms, Molds
Eukaryotic
Unicellular or Multicellular
Heterotrophic - external digestion
Cell wall of chitin
Animalia
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Ex: Animals, Humans
Eukaryotic
Multicellular
Hetrotrophic - internal digestion
No cell wall
Other Systems
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Multiple Kingdoms – split life into as many as
8 kingdoms. (review Chapter 28)
Domains – a system of classification that is
higher than kingdom.
3 Domain System
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Based on molecular structure for
evolutionary relationships.
Prokaryotes are not all alike and should be
recognized as two groups.
Gaining wider acceptance.
3 Domains
1. Bacteria – prokaryotic.
2. Archaea – prokaryotic, but biochemically
similar to eukaryotic cells.
3. Eucarya – the traditional eukaryotic cells.
Summary
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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.
Summary
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Recognize the 5 Kingdoms.
Recognize alternate systems for classification.
Know about Domains.