Life Science Lesson 7: Origin Theories

Lesson 7: Earth and Life - Theories About the Origin of Life

• Theories about the origin of life are explored.
• Life science examines living things.
• An individual living creature is called an organism.

Theories of Life Origins

• Spontaneous Generation:
  • Assumed life arises from non-living matter.
  • Ancient Greek philosopher Anaximander and Aristotle proposed this idea.
  • Aristotle believed that life emerged spontaneously from inanimate objects.
  • This theory was widely accepted for centuries.
• Challenges to Spontaneous Generation:
  • Francesco Redi (1668) challenged the theory. He demonstrated that maggots don't spontaneously appear on rotting meat.
  • He designed experiments with covered and uncovered jars of meat, showing maggots appeared only in uncovered jars, refuting the spontaneous generation theory.
  • John Needham (1745) supported spontaneous generation.
    • He boiled broth to kill microbes, but microbes still appeared.
  • Lazzaro Spallanzani (1768) improved on Needham's experiment.
    • Spallanzani showed that sealing the containers prevented the growth of microbes.
  • Louis Pasteur (1859) conclusively disproved spontaneous generation.
  • His experiment used swan-necked flasks.
    • Pasteur designed flasks with long, curved necks that allowed air in but prevented dust and microbes from entering the broth.
    • No microorganisms appeared in the broth. This definitively disproved spontaneous generation.
• Panspermia:
  • Life on Earth originated from a celestial source (e.g., space).
  • Proposed by astronomer Fred Hoyle in the 19th century.
  • Life's building blocks might have arrived on Earth via comets or other celestial bodies.
  • Some scientists suggest aliens may have brought the materials for life formation.
• Primordial Soup Theory:
  • Life began in a soup of organic molecules.
  • Proposed by Alexander Oparin and John Haldane.
  • Early Earth's atmosphere had gases like methane, ammonia, and hydrogen.
  • Energy like lightning sparked chemical reactions.
  • These reactions formed simple organic molecules that accumulated in pools of water.
  • Eventually, these molecules combined to form more complex molecules necessary for life.
• Miller-Urey Experiment:
  • Stanley Miller and Harold Urey tested the primordial soup theory in 1950.
  • They simulated the early Earth's atmosphere by creating a closed environment with methane, ammonia, hydrogen, and water.
  • Sparks were used to simulate lightning, creating organic molecules like amino acids and fatty acids.
  • The Miller-Urey experiment provided compelling evidence supporting the theory that simple organic molecules could be formed in early Earth conditions.