The Origin of Life on Earth

Chemical Evolution

• Conditions of life on earth. A reducing atmosphere on earth.  It contained no free oxygen.  The gases in the early atmosphere were methane, Hydrogen sulfide, ammonia, and water vapor
• Synthesis of Pre-biotic molecules occurred when energy was injected into this system from lightning.
• The pre-biotic soup collected these molecules in a watery environment which eventually became the ocean
• Salts and other compounds dissolved in water entered this system as run off
• The conditions in this soup led to the evolution of molecules in the ocean

Miller – Urey experiment

• http://www.ucsd.tv/miller-urey/.  A simulation of the Miller-Urey experiment
• Had an atmospheric compartment containing the gases in the primordial conditions on the earth
• Had an oceanic compartment containing water
• Atmospheric compartment is exposed to sparks to simulate lightning
• A condenser cools the gases producing condensed molecules
• These molecules are collected in the oceanic compartment
• The compounds react in the oceanic compartment to produce amino acids and purines and pyrimidines
• Amino acids formed in the Miller-Urey experiment wer a mixture of D and L forms.  Recent experiments have shown that the L- amino acids are selected
• The original molecules in the experiment have been revised to include H2S to account for the violent volcanic eruptions
• The polymerization reactions which are the basis for life on earth occurred in the soup – The monomers seem to have bound to fine particles of clay
• The most probable location for the emergence of life is the edges of oceans – Others feel that there is a possibility that life emerged in extreme environments such as the hydrothermal vents.

Catalytic RNAs

·         Enzymes are essential agents in living systems that catalyze four of the biochemical reactions with extraordinary speed and precision.

·         Although enzymes made of protein are the dominant form of biocatalyst in modern cells, there are at least eight natural RNA enzymes, or ribozymes, that catalyze fundamental biological processes.

·          It is believe that these ribozymes might be the remnants of an ancient form of life that was guided entirely by RNA.