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內容試閱：
Origin of Life
There are many different theories concerning where the origin of life occurred. Some of these theories are more credible than others, yet all provide an interesting explanation for lifes beginnings.
One early explanation, known as the Materialistic Theory or Physico-chemical Theory, was proposed independently by two scientistsA.I.Oparin, a Russian scientist in 1923 and J.B.S Haldane, an English scientist in 1928. It states that the origin of life on earth is the result of a slow and gradual process of chemical evolution that probably occurred about 3.8 billion years ago. This theory was the precursor of another theory called abiogenesis, also known as spontaneous generation, which studies how life on Earth could have arisen from inanimate matter. It suggests that life began in water as a result of the combination of chemicals from the atmosphere and some form of energy to make amino acids, the building blocks of proteins, which would then evolve into all the species.
Essential to this spontaneous origin of life was the availability of organic molecules as building blocks. Already in 1922 Oparin had proposed that the early Earth had a reducing atmosphere comprised mainly of ammonia, methane, and large amounts of hydrogen. Later in 1953 , Stanley Miller successfully carried out the famous Miller-Urey experiment which showed that amino acids could be produced under a condition where a mixture of methane, hydrogen, ammonia and water is reacted in a spark discharge apparatus, the condition similar to those on the primitive Earth.〇1 The idea of spontaneous generation was popular almost till seventeenth century, supported by many scientists like Descartes, Galileo and Helmont.
Toward the end of the 19th century and the beginning of the 20th century, as scientists were learning about the genetic and biochemical complexity of the cell, confusion about the origin of life grew. One way around the problem was to say that life had never emerged, but
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