Labels:bulletin board | reckoner OCR: The primary paleontological fact about life's beginnings points to predi ictability for the onset and very little for the particular pathways thereafter The earth is 4.6 billion years oid but the oldest rocks date to about billion years because the earth's surface became molten early in its history result of bombardment by large amounts of cosmic debris during the solar system's coalescence and of heat generated by radioactive decay of short- lived isotopes These oldest rocks are too metamorphosed by subsequent heat aud pressure to preserve fossils (though some scientists interpret the proportions of carbon isotopes in these rocks as signs of organic production) The oldest rocks sufficiently unaltered to retain cellular fossils African and Australian sediments dated to 3.5 billion years ol ...
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