Wikibooks: Developing A Universal Religion/Life/Development Of Life On Earth
While we don’t definitively know where life first developed we do know approximately when it first appeared on Earth—it showed up less than a quarter of a billion years after the Earth’s crust had formed. In other words just about as soon as it could. It should be noted that complex (i.e. multicellu...
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| Language: | English |
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| Online Access: | https://en.wikibooks.org/wiki/Developing_A_Universal_Religion/Life/Development_Of_Life_On_Earth |
| Summary: | While we don’t definitively know where life first developed we do know approximately when it first appeared on Earth—it showed up less than a quarter of a billion years after the Earth’s crust had formed. In other words just about as soon as it could. It should be noted that complex (i.e. multicellular) life forms could not have existed anywhere in our universe during the first third or so of its life. It takes several billion years for most stars to burn then collapse so producing the novae and supernovae that make and release the heavier chemical elements that partly constitute all planets and life as we know it. It has taken another four billion years for life on this planet to evolve into us. Complex life is a relative late comer to the universe’s party. For reasons noted in the introduction to this chapter early evidence of life is hard to come by. See Sarah Simpson “Questioning the Oldest Signs of Life ” Scientific American April 2003 70 77 for a recent review of this topic. Nevertheless indirect evidence suggests that it was present at least 3.7 billion years ago. This has been deduced from an analysis of rocks dating to that age found on an island close to Greenland. These rocks contain a higher carbon 12 to carbon 13 isotopic ratio than chemical and physical processes alone would create. (Life processes prefer the lighter isotopes and this concentrates carbon 12 where life exists.) More direct evidence in the form of fossil micro organisms has been discovered in sedimentary rocks from Iceland that are between 3.7 and 3.8 billion years old. (Iceland is particularly suitable for finding early life forms because its rocks have not been greatly disturbed by geological processes during the intervening ages.) Many of us were taught in school that there are three kingdoms of life on this planet. Research carried out by some two hundred scientists from a dozen countries led them to recently state that there are at least five major kingdoms animals fungi green plants red plants and brown plants. ... |
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