Origins of Life• Early Idea: Spontaneous

Generation– The idea that non-living

material can produce life—Life magically appears!

– Examples• Meat produces maggots• Mud produces fish

(mudskippers)• Grain produces mice

Origins of Life

• Francesco Redi was first to disprove the theory of spontaneous generation in 1668– Experiments with rotting meat

Origins of Life • Also during this time, scientists were

just beginning to use microscopes…

– They were able to see that microorganisms were EVERYWHERE!

– Even though Redi was able to disprove the theory of spontaneous generation, many scientists thought that microorganisms arose spontaneously from a “vital force” in the air

Origins of Life

• Louis Pasteur– Disproved the spontaneous generation of

microorganisms – Experiments with broth

Origins of Life

• Pasteur’s experiments showed that microorganisms do not arise from the broth alone even in the presence of air

• Biogenesis became the accepted theory about the origin of life– Biogenesis is the idea that living

organisms only come from other living organisms

How Did Life Begin On Earth?

• Early Earth– Very Hot – Meteorite Collisions – Volcanoes– Very little oxygen

• Atmosphere made of H2O Vapor, CO2, N gas, CH4 & NH3

• Ingredients for Life: Before life can occur, you need the molecules of life– 1st – Formation of simple organic molecules – 2nd – Organization into complex organic

molecules• Proteins / Carbohydrates / Nucleic Acids / Lipids

• So… How did this happen in such a harsh environment?

How Did Life Begin On Earth?

• Miller & Urey (1953) – Tested theory by simulating

conditions on early Earth in a lab– Mixture of H20 vapor, NH3, CH4,

and H gasses was zapped with electrodes

– Cooled gasses condensed in flask

– After a week, several kinds of amino acids, sugars, and other small organic molecules were present in the flask

How Did Life Begin On Earth?

• The next steps in the origin of life were the formation of complex organic molecules and cells

• Heat caused the amino acids to form proteins and also caused the production of ATP and nucleic acids

• Doing this formed “protocells” – or large ordered structures, enclosed by a membrane that carries out life functions

How Did Life Begin On Earth?

The First True Cells

• First forms of life were prokaryotes that likely evolved from protocells– Anaerobic Heterotrophs

– Later, early prokaryotes evolved to be able to make their own food • These were similar to archaebacteria

and used chemosynthesis to produce their food

The First Photosynthetic Prokaryotes

• Likely the next kind of organisms to have evolved– Were able to use sun to make

glucose

– Produced OXYGEN, which changed Earth’s atmosphere

– Lightening + Oxygen = Ozone Layer formation

The Endosymbiont Theory

• Lynn Margulis, in 1960’s• Eukaryotes evolved from prokaryotes as a

result of symbiotic relationship between prokaryotic bacteria