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Bell Ringer

Bell Ringer

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Bell Ringer

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  1. Bell Ringer • What is the theory of evolution? • How do fossil records prove this theory? Give two examples of animal fossils found that give evidence to support the theory of evolution.

  2. Chapter 9.3Relative Age of Rocks Mr. Perez

  3. Important Vocabulary • Sedimentary rock • Principle of superposition • Relative age • Unconformity

  4. Oldest Rocks on the Bottom • According to the law of superposition, in undisturbed layers of rock, the oldest rocks are on the bottom and the rocks become progressively younger toward the top

  5. Rock Layers • Why do younger rock layers pile up on older rock layers??? • BECAUSE… • Sediment accumulates in horizontal beds, forming layers of sedimentary rock • The first layer that forms is at the bottom • The next layer forms on top of the previous one • And so on… • HOWEVER… • Forces generated by mountain formation can turn layers over • When this happens, other clues in the rock layer can help us determine their original positions and relative ages.

  6. Relative Ages • The relative age of something is its age in comparison to the ages of other things • Geologists can determine the relative age of rocks by examining their places in a sequence. • Relative age does not tell you the age of rock in actual years… you only know if a rock layer is older or younger

  7. Other Clues Help • Finding the relative age is easy, if the rock haven’t been faulted or turned upside down. • In layers that have been disturbed you may have to find fossils and other clues to date the rocks • Example- If Mr. Perez finds a fossil in the top layer of rock that is younger than a fossil in the bottom layer, we can hypothesize that the layers have been turned upside down by folding during mountain building

  8. Unconformities • Unconformities are gaps in a sequence of rock layers that is due to erosion or periods without any deposition (new sediments falling) • Three types of unconformities: • ANGULAR UNCONFORMITY • DISCONFORMITY • NONCOMFORMITY

  9. Angular Unconformity • Angular Unconformities Form when… • Horizontal layers of sedimentary rock are tilted and uplifted • Erosion and weathering wear down tilted layer • Younger sediment are deposited on top of tilted layer

  10. Disconformity • Disconformity forms when… • Sedimentary rock layers have been formed • Erosion occurs, not completely removing a layer- No deposition occurs as time passes • Younger rocks form above the erosion surface when deposition of sediments begins again • This causes a gap to form in the rock record.

  11. Nonconformity • Nonconformities form when… • Metamorphic or igneous rock are uplifted • Erosion occurs • Sedimentary rocks are deposited on top of this erosion surface • Sometimes rock fragments from below are incorporated into sediments deposited above

  12. Matching up Rock Layers • Evidence used for correlation: • Fossils- if the same types of fossils are found in the same type of rock layer in two different locations • Other dating methods- testing of rocks in the lab

  13. Resources • Florida Science Grade 7 Glencoe Science & McGraw Hill Publishing • Google Images