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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.
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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.
