lecture08 - History of Earth and Life Lecture 8 1 Lecture 8...

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History of Earth and Life Lecture 8 1 Lecture 8 - Time indicators, Radioisotopes, Time scale Isotopes Chemical Elements nucleus protons (positively charged particles) neutrons (neutral particle) electrons (negatively charged particles) Atomic number - number of protons; defines chemical properties and is constant (C=6; O=8) Atomic mass number - number of protons + neutrons Atomic mass number may vary. Isotopes - Atoms of the same element that differ in their atomic mass number (e.g., Carbon =12, 13, 14) Stable Isotopes Remain stable through time (atomic mass number) Many isotopes are stable 12 C, 13 C, 16 O, 17 O, 18 O Useful: Their ratios provide records of past conditions on or within the Earth Radioactive Isotopes (e.g. 14 C, 40 K, 235 U) Unstable, decay to form other isotopes or elements Useful: Can be used to date objects containing them Decay of Radioactive Isotopes Parent isotopes - unstable, radioactive isotope that undergoes decay process Daughter isotopes - stable isotopes derived as a final product of decay process Intermediate daughter isotopes - intermediate products during decay from parent isotope to stable daughter isotope Parent Isotope Daughter Isotope+Nuclear Emission+Heat Isotopes may decay in a series of steps involving intermediate daughter isotopes (e.g.,
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