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The Composition of the Earth

The Composition of the Earth. The earth is composed of 92 elements Elements are made of atoms Atoms are made of protons (+) neutrons (o) electrons (-) Isotopes are atoms with varying numbers of neutrons ex Cl 35 and Cl 37. Radioactivity.

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The Composition of the Earth

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  1. The Composition of the Earth The earth is composed of 92 elements Elements are made of atoms Atoms are made of protons (+) neutrons (o) electrons (-) Isotopes are atoms with varying numbers of neutrons ex Cl35 and Cl37

  2. Radioactivity • This is a spontaneous decay of unstable forms of elements called radioisotopes • During the decay, three things can happen 1) p  n 2) n  p 3) atom  smaller element • Ex. U238 Pb236

  3. Details on Radioactive Decay • During decay there is an emission of particles such as 1) beta decay (electrons or positrons / anti electrons) 2) alpha decay (2 protons or 2 neutrons)

  4. Using Radioactive Decay in Dating • Each radioactive element has a unique half-life which is the amount of time in which ½ of the starting mass has decayed • Ex. The half life of C14 is 50,000 yrs If you start with 1 kg at time zero 0.5 kg at time 50 000 0.25 kg at time 100 000 0.125 kg at time 150 000 yrs

  5. Radiometric dating cont’d • A radioactive element is assumed to have a certain concentration when a rock / substance is formed. • The decay rate is constant • The amount of the radioactive element remaining is compared to the assumed initial concentration • Age is determined.

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