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Absolute Dating

Absolute Dating. Absolute Dating. Absolute Dating determines the actual age of a rock or fossil in years. The main method of absolute dating is RADIOMETRIC DATING. How Radiometric Dating Works.

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Absolute Dating

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  1. Absolute Dating

  2. Absolute Dating • Absolute Dating determines the actual age of a rock or fossil in years. • The main method of absolute dating is RADIOMETRIC DATING.

  3. How Radiometric Dating Works • Radioactive elements are elements with atoms that give off particles (radiation) from their nuclei. This is called Radioactive Decay. • Atoms give off particles to become new lighter, more stable elements. Decay will continue until the new element is stable and not radioactive.

  4. Rate of Decay • Radioactive elements decay at CONSTANT RATES. As soon as a rock forms with radioactive elements in it, decay begins. We use this to find the age of a rock. • The rate at which an element decays into a new element is measured as a HALF LIFE.

  5. Half Life • A HALF LIFE is the amount of TIME it takes for HALF of atoms of a radioactive element to decay into a new, stable element. • Terms used to describe material: • Parent Material: the original, radioactive element • Daughter Material: the new, stable element

  6. Example 100 % Parent Material Time= 0 The rock formed 50 % Parent, 50% Daughter 1 Half Life 25% Parent, 75% Daughter 2 Half Lives 12.5 % Parent, 87.5 % Daughter 3 Half Lives 6.25% Parent, 93.75 % Daughter 4 Half Lives

  7. Graph of data: Decay Curve 100 % Parent 50 25 12.5 6.25 4 1 2 5 3 Half Lives

  8. Using Half Life to find Age • If you know the number of years there are in an elements half-life, you can figure out the age of a rock. • The number of years in an elements’ half-life would be the number of YEARS it takes for HALF of the radioactive elements in the rock to turn into stable elements.

  9. Example • The number of years in a half-life for Carbon-14 is 5,730. • So….. If one half-life has passed, the rock is 5,730. If two half-lives have passed, the rock is 11,460 years old.

  10. Samples of Half-Lives

  11. Questions • If a rock contains 50% parent material, how many half-lives have passed? • If a rock contains 12.5 % parent material, how many half-lives have passed? • If a rock’s half-life is 25 years, and two half-lives have passed, how old is the rock? • If a rock’s half-life is 50 years, and three half-lives have passed, how old is the rock?

  12. Half Life, 1/2

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