THE HISTORY OF LIFE ON EARTH

• Protocells are the primitive form of the cell
• Chemical and physical processes that produced the first cells

  1. Abiotic synthesis of small organic molecules created the building blocks of life from non-life
  2. Joining of these small molecules into macromolecules
  3. Packaging of molecules into protocells
  4. Origin of self-replicating molecules
• Earth formed about 4.6 billion years ago
• 4.6 billion years ago, Earth

  • was bombarded by rocks and ice
  • Vaporized water prevented seas from forming before about 4 billion years ago
  • Early atmosphere had little oxygen and likely contained water vapor and chemicals released by volcanic eruptions
• Gases present in the Earth's atmosphere 4.6 billion years ago


  Nitrogen and oxides, CO2, CO4, ammonia, and hydrogen
• Hypothesis/theories of Earth's origin

  • Oparin and Haldane hypothesis
  • Primordial soup theory
  • Hydrothermal theory
  • Meteorite hypothesis
  • RNA hypothesis
  • Clay hypothesis of life
• Hydrothermal theory

  • Life started underneath the ocean 
  • Organic compounds may have been produced in deep-sea hydrothermal vents
• Hydrothermal vents


  areas on the seafloor where hot water and minerals gush from Earth’s interior into the ocean
• What environmental conditions support the hydrothermal theory?

  With proper PH/alkalinity (9-11) and temperature (40 to 90 degrees Celsius), stable organic compounds can be formed
• In the meteorite hypothesis, Murchison meteorite contains more than 80 amino acids
• In the RNA hypothesis, because they are single stranded RNA developed first before DNA
• Montmorillonite clay can have acted as a catalyst to polymerize certain molecules 
• In the RNA hypothesis, RNA can fold in itself and act as an enzyme
• In the RNA hypothesis, RNA molecules called ribozymes have been found to catalyze many different reactions
• It is thought that natural selection produces self-replicating ribozyme
• ribozymes can make complimentary copies of short stretches of RNA
• If you have a single stranded RNA, you can create the blueprint of DNA
• First cells may have formed fluid-filled vesicles with membrane-like structure
• The key characteristics of life, replication and metabolism, were present in protocells
• Montmorillonite clay increases the rate of vesicle formation
• Vesicles can absorb organic molecules attached to montmorillonite particles through a selectively permeable bilayer
• Fossils are preserved remnants of previously living organisms
• Sedimentary rocks are sources of fossils
• Stromatolites can be found in Canada and Australia
• Stromatolites are fossils of prokaryotes
• Only hard parts such as shell and bone are preserved in fossils; flowers and plants are difficult to preserve
• Radiometric dating is used to find the age of rocks/fossils 
• Radiometric dating Needs radioactive isotopes
• In radiometric dating, uranium is used in nuclear reactors
• Fossils contain isotopes that accumulated in the organisms when they were alive
• Carbon-14 decays into carbon-12 in radiocarbon dating
• Radiocarbon dating can be used to date fossils up to 75,000 years old
• The Geologic record is divided into eons

  1. Hadean
  2. Archaean
  3. Proterozoic
  4. Phanerozoic
• Plants called gymnosperms were active during the Jurassic period
•  Ediacaran period had few well-preserved fossils
• Fossils of flowering plants first appeared in the Cretaceous period
• The current period is quaternary
• In the Hadean period, there were no living organisms
• Billion of years later after the Hadean did prokaryotes appear during the Archaean period
• Stromatolites date back to 3.5 billion years ago