Two Theories of Origin of Life on Earth

Theory #1: Spontaneous Generation
• Spontaneous Generation = the theory that life can be created from non-living things
• Examples discussed in class: maggots arising from meat, mice from rice, and mould from bread
• The theory of Spontaneous Generation was disproved by Louis Pasteur by performing his experiment.
(Recall: broth was sterilized and left to sit. Broth in an airtight environment did not change, but broth exposed to air grew clumps of bacteria/mould. Conclusion: the “life” came from outside the container, not from the non-living broth)

Theory #2: Abiogenesis
How did the first life on Earth arise?
• Earth’s early environment (called Primordial soup) ≈ 3.5 billion years ago!
• Consisted of these gases: Water vapor, hydrogen gas, methane gas, ammonia gas
• Three energies (thermal, electrical, and solar) helped the change from primordial soup to simple organic molecules (amino acids, fatty acids, nucleic acids, simple sugars)
• -> means reacted or combined to form
• Primordial soup -> simple organic molecules -> complex organic molecules -> first true cells -> tissues -> organs -> organ systems -> organism
• Abiogenesis literally means birth of life from non-life
• Abiogenesis is the chemical evolution of life (not the same as the biological evolution of life.) In the process shown above, it is: Primordial soup -> simple organic molecules -> complex organic molecules -> first true cells (which are the smallest living things)
• Biological evolution is the progress of change from one living thing to another living thing. In the process shown above, it is the progress starting from the first true cells -> tissues -> organs -> organ systems -> organism <-> other organism
• <-> means transformed into

Support for this theory:
• Alexandar Oparin: combined gum Arabic + gelatin to make coacervates
• Coacervates = groups of organic molecules having some of the functions/properties of simple cells. Not quite living, but closer!
• Oparin’s hypothesis: life began in the ocean and from substances present in the atmosphere