Lecture17 - Quote of Day The disadvantage of men not...

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Quote of Day The disadvantage of men not knowing the past is that they do not know the present. History is a hill or high point of vantage, from which alone men see the town in which they live or the age in which they are living. ( G. K. Chesterson ) http://www.inspirational-quotes.info/history-quotes.html
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Geologic Time
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Last lecture we focused on the topic of relative time and how geologists decipher the relative order of events in earth’s history. This lecture we will focus on the topic of absolute time and how geologists determine the absolute ages of events. oldest youngest Born in 1970 Born in 1999 Relative time Absolute Age
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Dating with radioactivity 1. Three basic components of an atom => protons (+), neutrons, and electrons (-) 2. Proton and neutrons reside in the center (nucleus) of the atom 3. An element is defined by the number of protons (“atomic number”) 4. The number of neutrons can vary among atoms of the same element. Such atoms are called isotopes 5. Some isotopes are stable through time (stable isotopes); others change through time ( radioactive isotopes ) 6. The most common methods used by geologists to determine absolute ages involve radioactive isotopes.
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Radioactivity ¾ Spontaneous change (decay) in the structure of an atom’s nucleus ¾ Three basic types of radioactive decay Alpha emission Emission of 2 protons and 2 neutrons (an alpha particle) Mass number is reduced by 4; atomic number is lowered by 2 Beta emission An electron (beta particle) is ejected from nucleus Mass number remains unchanged; atomic number increases by 1 Electron capture An electron is captured by nucleus and combines with a proton to form a neutron Mass number remains unchanged; atomic number decreases by 1 Dating with radioactivity Figure 9.13
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Important terms Parent – an unstable radioactive isotope Daughter product – the isotopes resulting from the decay of a parent Half-life – time required for one-half of radioactive nuclei in sample to decay ¾ Principle of radioactive dating Percentage of radioactive atoms that decay during one half-life is always the same (50%) However, the actual number of atoms that decay continually decreases Comparing the ratio of parent to daughter yields the age of the sample Dating with radioactivity Example: Flipping a dime to simulate radioactive decay. “Heads” represents a “parent atom” and tails represents a “daughter product”. We will flip the coins
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This note was uploaded on 04/18/2011 for the course EAS 101 taught by Professor Kirschner during the Spring '11 term at Saint Louis.

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Lecture17 - Quote of Day The disadvantage of men not...

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