The Changing Earth Chapter 4: Views of Earth’s Past
Section 4.1 Earth’s Past is Revealed in Rocks and Fossils
Rocks, fossils, and original remains give clues about the past. <ul><li>Fossils: traces or remains of living things from l...
Continued – See page 112
Continued <ul><li>Fossils form in several different ways.  Molds and casts form in sedimentary rock. </li></ul><ul><ul><li...
Continued – See page 113
Continued – See page 115 Some fossils are not original remains, but rather impressions or traces made of rock.  They provi...
Continued <ul><ul><li>Petrified Wood is the stone fossil of a tree.  It forms when minerals take the place of the tree’s c...
Continued <ul><li>Trace fossils are pieces of indirect evidence of an organism’s presence, such as preserved footprints, t...
Fossils and other natural evidence show changes in life and the environment. <ul><li>Tree rings: vary in width, according ...
Continued <ul><li>Ice cores: tubular samples of layers of snow and ice that built up over thousands of years. </li></ul><u...
Section 4.2 Rocks Provide a  Timeline for Earth
Layers of sedimentary rocks show relative age. <ul><li>Relative age: the age in relation to other objects or events. </li>...
Continued – See page 120
Continued – See page 121
Continued <ul><li>Index fossils are fossils of organisms that: </li></ul><ul><ul><li>Were common (abundant). </li></ul></u...
Continued – See page 122
Radioactive dating can show absolute age. <ul><li>Absolute age is the actual age.  It can be determined by radioactive dat...
Continued – See page 123
Continued Sr-87 Strontium 47.0 billion years Rb-87 Rubidium Pb-208 Lead 14.1 billion years Th-232 Thorium Pb-206 Lead 4.5 ...
Continued – See page 124 Scientists use the breakdown or radioactivity of atoms to determine relative ages of rocks.
Section 4.3 The Geologic Time Scale Shows Earth’s Past.
Earth is constantly changing. <ul><li>The theory of uniformitarianism states that: Earth is always changing, and the same ...
Geologic time scale divides Earth’s history. <ul><li>Intervals are defined by major events or changes on Earth.  The divis...
 
Continued – See page 130
Continued – See page 131
Continued – See page 132
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Chapter 4 Views of Earth's Past

  1. 1. The Changing Earth Chapter 4: Views of Earth’s Past
  2. 2. Section 4.1 Earth’s Past is Revealed in Rocks and Fossils
  3. 3. Rocks, fossils, and original remains give clues about the past. <ul><li>Fossils: traces or remains of living things from long ago. </li></ul><ul><ul><li>Examples: preserved bones, imprints in rock, petrified wood, carbon films, original remains. </li></ul></ul><ul><ul><li>They provide direct evidence of organisms </li></ul></ul><ul><ul><li>They are found in places where conditions prevent normal decomposition, such as ice, amber, or tar. </li></ul></ul>
  4. 4. Continued – See page 112
  5. 5. Continued <ul><li>Fossils form in several different ways. Molds and casts form in sedimentary rock. </li></ul><ul><ul><li>Mold: visible impression of a decayed organism. </li></ul></ul><ul><ul><li>Cast: forms when the mold later fills with sediment that hardens into stone. </li></ul></ul>
  6. 6. Continued – See page 113
  7. 7. Continued – See page 115 Some fossils are not original remains, but rather impressions or traces made of rock. They provide indirect evidence of the organism (example: shoe print)
  8. 8. Continued <ul><ul><li>Petrified Wood is the stone fossil of a tree. It forms when minerals take the place of the tree’s cells. </li></ul></ul><ul><ul><li>Carbon films are detailed prints of organism’s left behind by the carbon contained in the organism’s cells after the organisms decay. </li></ul></ul>
  9. 9. Continued <ul><li>Trace fossils are pieces of indirect evidence of an organism’s presence, such as preserved footprints, trails, animal holes, and feces. </li></ul>
  10. 10. Fossils and other natural evidence show changes in life and the environment. <ul><li>Tree rings: vary in width, according to a tree’s yearly growth, which is determined by environmental conditions such as amount of rainfall. </li></ul><ul><ul><li>Scientists can create an accurate history of weather patterns over time. </li></ul></ul>
  11. 11. Continued <ul><li>Ice cores: tubular samples of layers of snow and ice that built up over thousands of years. </li></ul><ul><ul><li>By analyzing the air and dust trapped in an ice core, scientists can determine past events such as volcanic eruptions and changes in climate. </li></ul></ul>
  12. 12. Section 4.2 Rocks Provide a Timeline for Earth
  13. 13. Layers of sedimentary rocks show relative age. <ul><li>Relative age: the age in relation to other objects or events. </li></ul><ul><li>Sedimentary rock layers indicate the order of life, oldest on the bottom. </li></ul><ul><li>Igneous rock intrusions can be relatively dated using sedimentary layers. </li></ul>
  14. 14. Continued – See page 120
  15. 15. Continued – See page 121
  16. 16. Continued <ul><li>Index fossils are fossils of organisms that: </li></ul><ul><ul><li>Were common (abundant). </li></ul></ul><ul><ul><li>Lived in many different geographical areas. </li></ul></ul><ul><ul><li>Existed only during specific spans of time. </li></ul></ul><ul><li>Index fossils are particularly useful for estimating the age of rocks in which they are found. </li></ul>
  17. 17. Continued – See page 122
  18. 18. Radioactive dating can show absolute age. <ul><li>Absolute age is the actual age. It can be determined by radioactive dating, the process of measuring (in half lives) the rate of change of a radioactive element. </li></ul><ul><li>A half-life is the length of time it takes for half of the atoms in a sample of radioactive element to change from an unstable form into another form. </li></ul>
  19. 19. Continued – See page 123
  20. 20. Continued Sr-87 Strontium 47.0 billion years Rb-87 Rubidium Pb-208 Lead 14.1 billion years Th-232 Thorium Pb-206 Lead 4.5 billion years U-238 Uranium Ar-40 Argon 1.3 billion years K-40 Potassium Decay Product Half-Life Element Common Radioactive Elements Used for Dating Rocks
  21. 21. Continued – See page 124 Scientists use the breakdown or radioactivity of atoms to determine relative ages of rocks.
  22. 22. Section 4.3 The Geologic Time Scale Shows Earth’s Past.
  23. 23. Earth is constantly changing. <ul><li>The theory of uniformitarianism states that: Earth is always changing, and the same forces of change at work today were at work in the past. </li></ul><ul><li>Some changes occur rapidly: volcanic eruptions, earthquakes, etc. </li></ul><ul><li>Some changes occur gradually: erosion, weathering, etc. </li></ul><ul><li>James Hutton, the father of modern geology, proposed the theory in the 18 th century. </li></ul>
  24. 24. Geologic time scale divides Earth’s history. <ul><li>Intervals are defined by major events or changes on Earth. The divisions include: </li></ul><ul><ul><li>Eons: the largest unit of time. </li></ul></ul><ul><ul><li>Eras: subunit of an eon. </li></ul></ul><ul><ul><li>Periods: subunits of eras. </li></ul></ul><ul><ul><li>Epochs: subdivisions of periods. </li></ul></ul>
  25. 26. Continued – See page 130
  26. 27. Continued – See page 131
  27. 28. Continued – See page 132
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