The History of Life on Earth

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The History of Life on Earth

• Chapter 4 section 4.1
• Chapter 25 sections 25.1 and 25.3

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Origin Of Life

• Earth formed 4.6 billion years ago
• When, and how did life originate?
• Life is believed to have begun 3.5 billion years
  ago
• What was the primitive environment of Earth like?
• Reducing, electron adding, atmosphere
• No electron hogging oxygen gas was present

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Step One Chemical Evolution

• Oparin and Haldane
• Reducing atmosphere high energy levels
  contributed to spontaneous chemical evolution
• Sidney Fox
• Spontaneous polymerization occurs on hot sand or
  clay
• Produced protenoids

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Protobionts

• Maintain different internal environment
• Microspheres selectively permeable protein
  membrane
• Displays osmotic swelling
• Stores energy
• Has a membrane potential
• Liposomes lipid bilayer
• Grow and appear to split give birth

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• Coacervates polypeptides, nucleic acids, and
  polysaccharides
• Hydrophobic macromolecules surrounded by shell of
  water molecules
• Can absorb substrates
• Release products
• May have enzymes associated with them
• In chemical evolution the environment selects for
  best suited molecules to survive
• What ingredient necessary for life is missing in
  all protobionts?
• No hereditary material that would ensure
  continuity

6
Which Came First RNA or DNA?

• RNA!
• RNA has the following properties
• Less complex than DNA
• Less stable than DNA
• Has phenotype, can fold into diverse shapes
• Short strands of RNA can replicate
• Ribozymes, show enzymes can be non-protein
  molecules

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• Experiments have proven that RNA can evolve
• The RNA world was slowly able to direct protein
  synthesis and preserve and copy the genetic
  information
• As evolution continued different early cells
  showed varying success with life
• One trend resulted in DNA as the ultimate
  hereditary material
• RNA world ? DNA world

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Autotrophs vs. Heterotrophs

• Which came first autotrophs or heterotrophs?
• Heterotrophs obligate anaerobes
• Chemoautotrophs
• Photoautotrophs
• Oxygen in atmosphere results in mass extinctions
• Facultative aerobes survive
• Cellular Respiration evolves
• Eukaryotic organisms
• Multicellular organisms

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Characteristics of Protists

• Eukaryotic
• Most are unicellular
• Moist environments
• Mostly aerobic
• Flagella or cilia as extensions of cytoplasm
• Varied cell division, some reproduce sexually

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How did Eukaryotes Evolve?
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