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Main article: Origin of life
For religious beliefs about the creation of life, see creation myth.
Although it has not been pinpointed exactly, evidence suggests that life on Earth has existed for about 3.7 billion years.[12] All known life forms share fundamental molecular mechanisms, and based on these observations, theories on the origin of life attempt to find a mechanism explaining the formation of a primordial single cell organism from which all life originates. There are many different hypotheses regarding the path that might have been taken from simple organic molecules via pre-cellular life to protocells and metabolism. Many models fall into the "genes-first" category or the "metabolism-first" category, but a recent trend is the emergence of hybrid models that do not fit into either of these categories.[13]

There is no scientific consensus as to how life originated and all proposed theories are highly speculative. However, most currently accepted scientific models build in one way or another on the following theories:

Plausible pre-biotic conditions result in the creation of the basic small molecules of life. This was demonstrated in the Miller-Urey experiment, and in the work of Sidney Fox.
Phospholipids spontaneously form lipid bilayers, the basic structure of a cell membrane.
Procedures for producing random RNA molecules can produce ribozymes, which are able to produce more of themselves under very specific conditions.
The panspermia hypothesis proposes that life originated elsewhere in the universe and was subsequently transferred to Earth perhaps via meteorites, comets or cosmic dust

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