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|The Origin of Life on Planet Earth|
|Credit: Hawking, p120
The earth was initially very hot and without an atmosphere. In the course of time it cooled and acquired and atmosphere from the emission of gases from the rocks. The early atmosphere was not one in which we could have survived. It contained no oxygen, but a lot of other gases that are poisonous to us, such as hydrogen sulfide (the gas that gives rotten eggs their smell). There are, however, other primitive forms of life that can flourish under such conditions. It is thought that they developed in the oceans, possibly as the result of chance combinations of atoms into large structures, called macromolecules, which were capable of assembling other atoms in the ocean into similar structures. They would thus have reproduced themselves and multiplied. In some cases there would be errors in the reproduction. Most of these errors would have been such that the new macromolecules could not reproduce itself and eventually would have been destroyed. However, a few of the errors would have produced new macromolecules that were even better at reproducing themselves. They would have therefore had an advantage and would have tended to replace the original macromolecules. In this way a process of evolution was started that led to the development of more and more complicated, self-reproducing, organisms. The first primitive forms of life consumed various materials, including hydrogen sulfide, and released oxygen. This gradually changed the atmosphere to the composition that it has today and allowed the development of higher forms of life such as fish, reptiles, and ultimately the human race.
[This answer the Fundamental Question, which came first, the chicken or the egg. More importantly, it demonstrates the NEED for asking potentially productive questions.]
[This entry also relates to the entry dealing with the history of the planet, and help the misguided to think about what really happened, rather than blieving the fiction that the world is only six thousand years old.]