Chapter:  Clues to Earth’s Past Table of Contents Section 3:  Absolute Ages of Rocks Section 1:  Fossils Section 2:  Relat...
Absolute Ages <ul><li>Absolute age  is the age, in years, of a rock or other object.  </li></ul><ul><li>Geologists determi...
Radioactive Decay <ul><li>Some isotopes are unstable and break down into other isotopes and particles. </li></ul><ul><li>S...
Alpha and Beta Decay <ul><li>In some isotopes, a neutron breaks down into a proton and an electron. </li></ul><ul><li>This...
Alpha and Beta Decay Absolute Ages of Rocks 3
Alpha and Beta Decay Absolute Ages of Rocks 3
Half-Life <ul><li>The  half-life  of an isotope is the time it takes for half of the atoms in the isotope to decay. </li><...
Radiometric Ages <ul><li>As time passes, the amount of parent isotope in a rock decreases as the amount of daughter produc...
Radiometric Ages Absolute Ages of Rocks 3
<ul><li>By determining the amounts of the isotopes in a sample, scientists can evaluate how much the isotope ratio in the ...
<ul><li>This is because many sedimentary rocks are made up of particles eroded from older rocks. </li></ul>Age Determinati...
<ul><li>By dating meteorites and using other evidence, scientists have estimated the age of to be about 4.5 billion years....
Uniformitarianism <ul><li>Before the discovery of radiometric dating, many people estimated that Earth is only a few thous...
<ul><li>He used the principle of  uniformitariansm . This principle states that Earth processes occurring today are simila...
Uniformitarianism Absolute Ages of Rocks 3 <ul><li>Today, scientists recognize that Earth has been shaped by two types of ...
Section Check 3 Question 1 __________ age is the age in years of an object. A. Absolute B. Calculated C. Derived D. Relati...
Section Check 3 Answer The answer is A. Geologists use properties of atoms in specific materials to determine absolute age...
Section Check 3 Question 2 What is meant by the term “half-life” of an isotope?
Section Check 3 Answer The half-life of an isotope is the time it takes for half of the atoms in the isotope to decay.
Section Check 3 Question 3 What information must you have in order to conduct radiometric dating? Answer You must have an ...
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Chapter 3:3 Absolute Ages of Rocks

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  • Chapter 3:3 Absolute Ages of Rocks

    1. 2. Chapter: Clues to Earth’s Past Table of Contents Section 3: Absolute Ages of Rocks Section 1: Fossils Section 2: Relative Ages of Rocks
    2. 3. Absolute Ages <ul><li>Absolute age is the age, in years, of a rock or other object. </li></ul><ul><li>Geologists determine absolute ages by using properties of the atoms that make up materials. </li></ul>Absolute Ages of Rocks 3
    3. 4. Radioactive Decay <ul><li>Some isotopes are unstable and break down into other isotopes and particles. </li></ul><ul><li>Sometimes a lot of energy is given off during this process. </li></ul>Absolute Ages of Rocks 3 <ul><li>The process of breaking down is called radioactive decay . </li></ul>
    4. 5. Alpha and Beta Decay <ul><li>In some isotopes, a neutron breaks down into a proton and an electron. </li></ul><ul><li>This type of radioactive decay is called beta decay. </li></ul>Absolute Ages of Rocks 3 <ul><li>Other isotopes give off two protons and two neutrons in the form of an alpha particle. </li></ul>
    5. 6. Alpha and Beta Decay Absolute Ages of Rocks 3
    6. 7. Alpha and Beta Decay Absolute Ages of Rocks 3
    7. 8. Half-Life <ul><li>The half-life of an isotope is the time it takes for half of the atoms in the isotope to decay. </li></ul><ul><li>After two half-lives, one fourth of the original isotope still remain. </li></ul>Absolute Ages of Rocks 3 <ul><li>After three half-lives, one eighth of the original isotope still remain. </li></ul>
    8. 9. Radiometric Ages <ul><li>As time passes, the amount of parent isotope in a rock decreases as the amount of daughter product increases. </li></ul><ul><li>By measuring the ratio of parent isotope to daughter product in a mineral and by knowing the half-life of the parent, in many cases you can calculate the absolute age of a rock. This process is called radiometric dating . </li></ul>Absolute Ages of Rocks 3
    9. 10. Radiometric Ages Absolute Ages of Rocks 3
    10. 11. <ul><li>By determining the amounts of the isotopes in a sample, scientists can evaluate how much the isotope ratio in the sample differs from that in the environment. </li></ul>Radiometric Dating <ul><li>Carbon-14 is useful for dating bones, wood, and charcoal up to 75,000 years old. </li></ul>Absolute Ages of Rocks 3 <ul><li>Living things take in carbon from the environment to build their bodies. </li></ul><ul><li>After the organism dies, the carbon-14 slowly decays. </li></ul>
    11. 12. <ul><li>This is because many sedimentary rocks are made up of particles eroded from older rocks. </li></ul>Age Determination <ul><li>Aside from carbon-14 dating, rocks that can be radiometrically dated are mostly igneous and metamorphic rocks. </li></ul>Absolute Ages of Rocks 3 <ul><li>Most sedimentary rocks cannot be dated by this method. </li></ul>
    12. 13. <ul><li>By dating meteorites and using other evidence, scientists have estimated the age of to be about 4.5 billion years. </li></ul>The Oldest Known Rocks <ul><li>Radiometric dating has been used to date the oldest rocks on Earth. </li></ul>Absolute Ages of Rocks 3 <ul><li>These rocks are about 3.96 billion years old. </li></ul>
    13. 14. Uniformitarianism <ul><li>Before the discovery of radiometric dating, many people estimated that Earth is only a few thousand years old. </li></ul>Absolute Ages of Rocks 3 <ul><li>But in the 1700’s, Scottish scientist James Hutton estimated that Earth is much older. </li></ul>
    14. 15. <ul><li>He used the principle of uniformitariansm . This principle states that Earth processes occurring today are similar to those that occurred in the past. </li></ul>Uniformitarianism Absolute Ages of Rocks 3 <ul><li>Hutton’s principle is often paraphrased as “the present is the key to the past.” </li></ul>
    15. 16. Uniformitarianism Absolute Ages of Rocks 3 <ul><li>Today, scientists recognize that Earth has been shaped by two types of change: slow, everyday processes that takes place over millions </li></ul>of years, and violent, unusual events such as the collision of a comet or asteroid about 65 million years ago that might have caused the extinction of the dinosaurs.
    16. 17. Section Check 3 Question 1 __________ age is the age in years of an object. A. Absolute B. Calculated C. Derived D. Relative NC: 5.01
    17. 18. Section Check 3 Answer The answer is A. Geologists use properties of atoms in specific materials to determine absolute age. NC: 5.01
    18. 19. Section Check 3 Question 2 What is meant by the term “half-life” of an isotope?
    19. 20. Section Check 3 Answer The half-life of an isotope is the time it takes for half of the atoms in the isotope to decay.
    20. 21. Section Check 3 Question 3 What information must you have in order to conduct radiometric dating? Answer You must have an isotope with an appropriately short or long half-life. You must also know the isotope’s half-life and be able to measure the ratio of parent isotope to daughter product.

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