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There is no unanimous agreement on a theory about the origin of life. Any record would have been erased during the long history of turmoil on the Earth’s surface. However, it is known that it must have happened between 4. The Environment — Four and a half billion years ago, the proto-Earth was completing its formation. It was still covered with a thick layer of molten lava. A grazing collision occurred with the subsequent appearance of a transient ring around the Earth that rapidly become the Moon. Small cometary impacts persisted until about four billion years ago.
It was the only habitable zone at that time for very simple life. The Materials — The raw materials in the atmosphere of early Earth consisted mainly of nitrogen and traces of other molecules as shown in Figure 11-02a. The oxygen concentration started to rise only at about 3. 5 billion years ago with the proliferation of life.
It is the fluid that transports the molecular components from one place to another and facilitates the chemical reactions that keep life going. Water serves as a supporting and cleansing fluid, bearing nutrients to where they are needed and taking away wastes. Furthermore, water is the general purpose solvent for dissolving organic molecules. The high water content in our body has suggested to many biologists that life on Earth arose in the oceans. In fact, there is a rough correspondence between the content of such elements as calcium and potassium in seawater and in blood and tissues. In 1953 Stanley Miller mixed substances such as water, molecular hydrogen, methane, and ammonia in a flask. After passing electrical discharge as input energy to this mixture, the assembly rearranged into a host of organic molecules as shown in Figure 11-03b including amino and nucleic acids — the building blocks of life.
Note that glycine and alanine are the most abundant amino acids in both cases. Recent research indicates that they are probably the earliest building blocks for life. The materials of life can be summarized into one category — the reduced organic compounds. The process of reduction stores energy while the carbon in organic substance provides a versatile building block.