GEOL 1301 Fall 2014 Lecture 13 Outline of Last Lecture I. RadioactivityOutline of Current LectureII. Half-LifeWhat is half life and “parent and child”? The rate of decay for a particular isotope depends on the number of radioactive isotopes present: -dN/dt=λN or N=No e-λt or N/No =e-λt Decay time is often expressed as a half life – the time it takes 1⁄2 the parent atoms to change to child atoms. Starting with 1000 parent atoms, How many parents & children are there after One 1⁄2 life? Two 1⁄2 Lives? Three 1⁄2 lives? How long does it take to get rid of all the parent atoms? Many experiments have shown that Temp, pressure and magnetic fields do not change the 1⁄2life of an unstable isotope. Measuring Absolute Geologic Time These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.To measure age of a mineral: 1) count number of parent and child atoms 2) calculate %. 3) Use the graph to find the number of 1⁄2 lives. Multiply number of 1⁄2 lives by the number of years of each 1⁄2 life. Measuring Absolute Geologic Time To measure age of a mineral: 1) count number of parent and child atoms 2) calculate %. 3) Use the graph to find the number of 1⁄2 lives. Multiply number of 1⁄2 lives by the number of years of each 1⁄2 life. Using radioactive isotopes, the relative time segments based on fossil succession have been dated. One reason geoscientists have great confidence in both the relative time scale based on fossils and radiometric dating is because both methods, using completely different approaches, agree. In the 18th century, James Hutton thought the Earth was ageless: - “we find no vestige of a beginning, no prospect of an end.” In the 20th century radioactive dating indicated the Earth, and Solar system formed ~ 4.5 billion years B.P. In a few billion more years astronomers think the Sun will balloon into a Red Giant Star as it runs out of Hydrogen and engulf the
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