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The History of Life on Earth

The History of Life on Earth. Chapter 4 section 4.1 Chapter 25 sections 25.1 and 25.3. 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?

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The History of Life on Earth

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  1. The History of Life on Earth Chapter 4 section 4.1 Chapter 25 sections 25.1 and 25.3

  2. 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

  3. 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

  4. 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”

  5. 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

  7. 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

  8. 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

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

  10. How did Eukaryotes Evolve?

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