Earth's History

• 4 Main Stages of Production of Simple Cells:

  1. Nonliving synthesis of organic molecules such as amino acids & nucleotides
  2. Joining of these small molecules into macromolecules including proteins & amino acids
  3. Packaging of these molecules into protobionts
  4. Origin of self-replicating molecules that eventually made inheritance possible
• Conditions on Early Earth

  • thick w/ water vapor
  • volcanic eruptions
  • nitrogen, carbon dioxide, methane, ammonia, hydrogen, & hydrogen sulfide
• In 1953, Stanley Miller & Harold Urey created lab conditions comparable to that of early Earth

  • their apparatus yielded amino acids & other organic compounds
  • the atmosphere may not have had enough methane & ammonia
  • showed that abiotic synthesis of organic molecules is possible
• Abiotic Synthesis of Macromolecules

  • small organic molecules like amino acids are not sufficient for life
  • researchers have been able to produce amino acid polymers by dripping solutions of amino acids onto hot sand, clay, or rock
  • polymers formed spontaneously
  • these polymers may have acted as weak catalysts for reactions on early Earth
• What are the key properties of life?

  accurate replication & metabolism
• protobiont


  collection of abiotically produced molecules surrounded by a membrane or membrane-like structure; may have some properties of life like reproduction, metabolism, & keeping an internal environment different from that of its surroundings
• The first genetic material was probably RNA
• ribozyme


  an RNA molecule that functions as an enzyme, catalyzing reactions during RNA splicing
• DNA is more stable than RNA
• The fossil record is based on the sequence in which fossils have accumulated
• radiometric dating


  a method for determining the absolute ages of rocks & fossils that is based on the half-life of radioactive isotopes
• Radioactive isotopes decay at a constant rate
• half-life


  the amount of time it takes for 50% of a radioactive sample to decay
• Half-life is not affected by environmental variables
• How can magnetism of rocks provide dating information?

  • iron particles in the rock align themselves w/ the Earth's magnetism
  • when the rock hardens, the orientation is frozen in time
  • Earth's magnetism has reversed repeatedly in the past & affected the entire planet
  • we can match corresponding patterns in other places
• Mammals are tetrapods
• Mammals' Unique Anatomical Features

  • one lower jaw bone (dentary)
  • hinge between different bones
  • hammer, anvil, & stirrup in the ear
  • differentiated teeth
• geologic record


  the division of Earth's history into time periods grouped into 3 eons & further subdivided into eras, periods, & epochs
• Which period is the time where animals existed?

  Phanerozoic eon
• How many eras is the Phanerozoic eon divided into?

  3
• Which era is called the "age of reptiles"?

  Mesozoic