Download Early Earth and the Origin of Life

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 years old.
 Earth - 4.5 billion years old.
Prokaryotes
Fossil
Modern
Bacterial Mats
Point
 Life on earth started relatively soon after the earth was
formed.
Chemical Evolution
 The evolution of life by abiogenesis.
Steps
1. Monomer Formation
2. Polymer Formation
3. Protobiont Formation
4. Origin of Heredity
Primitive Earth Conditions
 Reducing atmosphere present.
 Simple molecules
 Ex: H2O vapor
 CH4 methane
 Hydrogen H2,
 Ammonia NH3
Complex Molecule Formation
 Requires energy sources:
 UV radiation
 Radioactivity
 Heat
 Lightning
Oparin and Haldane 1920s
 Hypothesized steps of chemical evolution from
primitive earth conditions.
Miller and Urey, 1953
 Tested Oparin and Haldane’s hypothesis.
 Experiment - to duplicate primitive earth conditions in
the lab.
Results
 Organic monomers formed including Amino Acids.
Other Investigator's Results
 All 20 Amino Acids
 Sugars
 Lipids
 Nucleotides
 ATP
Hypothesis
 Early earth conditions could have formed monomers
for life's origins.
Polymer Synthesis
 Problem:
 Monomers dilute in concentration.
 No enzymes for bond formation.
Possible Answer
1. Clay
2. Iron Pyrite
Explanation
 Lattice to hold molecules, increasing concentrations.
 Metal ions present which can act as catalysts.
Protobionts
 Aggregates of abiotically produced molecules.
 Exhibit some properties of life.
 Ex: Osmosis
 Electrical Charge
 Fission
Protobionts
Protobiont Formation
 Proteinoids + H2O  microspheres
 Liposomes + H2O 
lipid membranes
Coacervates
 Colloidal droplets of proteins, nucleic acids and sugars
surround by a water shell.
 Will form spontaneously from abiotically produced
organic compounds.
Summary
 Protobionts have membrane-like properties and are
very similar to primitive cells.
 Start for selection process that lead to cells?
Question ?
 Where did the energy come from to run these early
cells?
Answer
 ATP.
 Reduction of sulfur compounds.
 Fermentation.
Genetic Information
 DNA  RNA  Protein
 Too complex for early life.
 Other forms of genetic information?
RNA Hypothesis
 RNA as early genetic information.
Rationale
 RNA polymerizes easily.
 RNA can replicate itself.
 RNA can catalyze reactions including protein
synthesis.
 Ribozymes
Ribozymes
 RNA catalysts found in modern cells.
 e.g. ribosomes
 Possible relic from early evolution?
Molecular Cooperation
 Interaction between RNA and the proteins it made.
 Proteins formed may serve as RNA replication
enzymes.
Molecular Cooperation
 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
 Could easily supply the energy and chemical
precursors for chemical evolution.
 Most primitive life forms are the prokaryotes found in
or near these vents.
New Idea
 Life started in cold environments.
 Interface between liquid and solid
allows concentration of materials and
formation of polyomeres.
 Molecules last longer too.
Modern Earth
 Oxidizing atmosphere.
 Life present.
 Prevents new abiotic formation of life.
Hypothesis
 Life as a natural outcome of chemical evolution.
 Life possible on many planets in the universe.
Kingdom
 Highest Taxonomic category
 Old system - 2 Kingdoms
1. Plant
2. Animal
5 Kingdom System
 R.H. Whittaker - 1969
 System most widely used today.
Main Characteristics
 Cell Type
 Structure
 Nutrition Mode
Monera
 Ex: Bacteria, Cyanobacteria
 Prokaryotic
Protista
 Ex: Amoeba, Paramecium
 Eukaryotic
 Unicellular or Colonial
 Heterotrophic
Fungi





Ex: Mushrooms, Molds
Eukaryotic
Unicellular or Multicellular
Heterotrophic - external digestion
Cell wall of chitin
Plantae
 Ex: Flowers, Trees
 Eukaryotic
 Multicellular
 Autotrophic
 Cell wall of Cellulose/Silicon
Animalia






Ex: Animals, Humans
Eukaryotic
Multicellular
Hetrotrophic - internal digestion
No cell wall
Motile
Other Systems
 Multiple Kingdoms – split life into as many as 8
kingdoms.
 Domains – a system of classification that is higher
than kingdom.
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.
3 Domains
1. Bacteria – prokaryotic.
2. Archaea – prokaryotic, but biochemically similar to
eukaryotic cells.
3. Eucarya – the traditional eukaryotic cells.
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.
Summary
 Recognize the 5 Kingdoms.
 Know about Domains.