Where and how did life originate? The Origin of Life Where and how did life originate?

Spontaneous Generation The mistaken idea that life arises from non-life Examples: At one time, people thought that mice could be created by placing damp hay and corn in a dark corner and that mud could give rise to worms

*The results failed to convince most people until the mid 1800’s! Early Experiments Francesco Redi (1668) Common Belief: maggots (fly larva) arise spontaneously from rotting meat Redi’s Hypothesis – flies, not meat, produced other flies *The results failed to convince most people until the mid 1800’s!

Theory of Biogenesis Only living organisms can produce other living organisms Louis Pasteur (1800’s) Designed an experiment to show that biogenesis was true even for microorganisms (He also developed a vaccine against rabies)

*Experiment showed that microorganisms do not appear spontaneously. Pasteur’s Experiment Used a sterile nutrient broth that supports growth of microorganisms *Experiment showed that microorganisms do not appear spontaneously. Nutrient Broth – a liquid used to grow microorganisms. Currently used to test certain foods and dairy products for salmonella.

If life can only arise from life, how did the first life form appear? A series of chemical events in which complex organic molecules (amino acids) were generated from simpler ones

Modern Theories for the Evolution of the 1st Organisms Organic Molecule Hypothesis Miller-Urey Experiment Early Cell Structure Hypothesis Endosymbiosis Theory

Organic Molecule Hypothesis Simple organic molecules (amino acids) can be made from inorganic compounds Early Earth’s Conditions: Atmosphere = ammonia, water vapor, hydrogen gas and methane (NO OXYGEN) Due to temps above boiling point, any liquid water would be evaporated right away. Earth cooled, water vapor condensed to form water (lakes & seas) Over time, lightning and UV light stimulated complex reactions to create proteins (building blocks of life)

Miller-Urey Experiment (1953) *In a lab setting, they were able to simulate Earth’s early conditions, zap it with electricity and produce amino acids

Early Cell Structure Hypothesis First cells = prokaryotes (anaerobic) Why? They are Unicellular, smaller than Eukaryotes and don’t contain a defined nucleus or other organelles. Evidence: Currently live in extreme environments Examples: hot springs of Yellowstone or Hydrothermal Vents whose conditions are similar to early Earth

Endosymbiosis Theory Prokaryotic cells were involved in the evolution of eukaryotic cells Prokaryotes may have lived inside of Eukaryotes and become organelles such a chloroplasts and mitochondria Led to the evolution of photosynthetic organisms

Important: Oxygen became abundant AFTER the first life forms developed, NOT as a condition that allowed them to develop. Bacteria = 1st organisms After Earth cooled down, liquid water became abundant