The Origin of Life

The Earth’s Beginnings

- Scientists believe that the Earth was first formed as a molten mass about 4.5 billion years ago.

- As the Earth’s crust cooled, water vapor in the atmosphere condensed into oceans.

- Minerals from the Earth’s crust started to dissolve in the water. This formed the Primordial Soup.

- The atmosphere contained H2, H2O, CH4, and NH3. NO FREE OXYGEN! The atmosphere was reducing.

How Life Got “Started”

- Lightning, heat, and UV radiation supplied energy for random bonding to make inorganic molecules into organic molecules.

- Organic molecules began to slowly build up over time.- Since the atmosphere was reducing, these molecules

were very stable and they did not break down easily.- After a while, several macromolecules had been

formed and covered by protective spheres.- Think about phospholipids and hydrophobic/philic

interactions, polar molecules…

Stanley Miller’s Experiment

- In 1953, he set up an experiment that used the gases from Earth’s early atmosphere (H2, H2O, CH4, and NH3) to model early conditions on Earth.

- Miller zapped the gases with electricity to see how the energy would affect the bonds of the molecules, like lightning used to on early Earth.

- He ended up with some amino acids, lactic acid, and adenine.

The Development of Life- The first prokaryotic cells emerged about a billion years after the

formation of the Earth.- These cells were anaerobic heterotrophs (remember, no Oxygen in

the atmosphere…)- Eventually, cyclic photosynthesis evolved, allowing non-cyclic

photosynthesis to evolve after that.- This released Oxygen gas (O2) into the atmosphere, where it reacted

to form the Ozone (O3) layer, providing protection from UV rays.- Now that the atmosphere contained Oxygen, aerobic respiration

could evolve.

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