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7 BIOL 1001 Evidence for Evolution (Jan. 21) post-lect

Mass ex nc ons pakerns of ex nc on chance events

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Unformatted text preview: rect. E.  Both A and B are correct How is the fossil record dated? Naturally occurring radioisotopes •  238U •  14C •  210Pb •  137Cs Radioisotope Decay Product Half- life (yrs) Materials dated Useful Da2ng Range (years) 14C 14N 5 730 Shells, limestone, organic materials 100- 50 000 40K 40Ar 1.3 billion Whole volcanic rock 100 000 – 4.5 billion 87Rb 87Sr 47 billion Micas 10 million – 4.5 billlion + 238U 207Pb 710 million zircon 10 million – 4.5 billlion + 235U 206Pb 4.5 billion 10 million – 4.5 billlion + zircon Why can’t sedimentary rock be dated directly using radiometric da-ng? Hint: think of the way sedimentary rock would form… Igneous rock forma-on Sedimentary rock comprises grains from other rocks (igneous & metamorphic) à༎ date those rocks, not point in -me...
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