2. The Origin of Life

3. 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 H 2, H 2 O, CH 4, and NH 3. NO FREE OXYGEN! The atmosphere was reducing.

4. 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…

5. Stanley Miller’s Experiment -In 1953, he set up an experiment that used the gases from Earth’s early atmosphere (H 2, H 2 O, CH 4, and NH 3 ) 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.

6. 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 (O 2 ) into the atmosphere, where it reacted to form the Ozone (O 3 ) layer, providing protection from UV rays. -Now that the atmosphere contained Oxygen, aerobic respiration could evolve.