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	Podcast:		25. Early Earth and Life Processes
	Episode:		Specificity of Life
	Category:		Science & Medicine
	Duration:		00:01:21
	Publish Date:		2011-07-28 08:52:39
	Description:		Transcript: The history of life on Earth is a story of experimentation; initially, the experimentation of chemical reactions, then the experimentation of biological processes, and finally that of genetic variation itself. These genetic variations and earlier variations are molded to the environment, which ensures the survival of the fittest organisms; this is the basis of natural selection. At a chemical and biochemical level, life has formed specific and efficient solutions to its problems, usually for energy efficiency reasons. Life uses only 20 of the 92 elements in the periodic table for its essential processes. It uses 20 out of 100,000 possible amino acids. It uses 10,000 out of a nearly infinite number of possible proteins. Many complex molecules have two-handedness, or mirror images of themselves. Early on in the history of life, life selected one of the two-handedness; for example, all the amino acids in life on Earth use the left-handed molecule, not the right-handed molecule. This, incidentally, is the reason we do not believe life originated from space, because in meteorites equal numbers of left- and right-handed molecules are observed.
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