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Chapter 21

Chapter 21. Fossils and the Rock Record. Geologic History Principles. Law of Uniform Processes Law of Superposition Law of Cross-cutting Relationships Law of Included Fragments. Law of. Uniform Processes.

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Chapter 21

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  1. Chapter 21 Fossils and the Rock Record

  2. Geologic History Principles • Law of Uniform Processes • Law of Superposition • Law of Cross-cutting Relationships • Law of Included Fragments

  3. Law of Uniform Processes • The processes which are changing the earth’s surface today are the same processes which acted in the past

  4. Law of Superposition • The oldest rock layer is on the bottom of an undisturbed rock column, and each higher layer is younger

  5. Law of Cross-cutting Relationships • A fault or intrusion is younger than the rock layers it cuts through

  6. Law of Included Fragments • Pieces of one rock found in another rock must be older than the rock in which they are found

  7. Tree Rings • This tree was approximately how old? About 17 years How did you determine this age? By counting the number or light (summer) and dark (winter) rings

  8. Geologic Time Scale • Which represents the longest time interval – era, eon, or epoch? • Which of the three eras represents the longest amount of time? • Approximately how old is the earth? eon paleozoic 4.6 billion years

  9. A B C D E F G X H I J K L Y Relative Age: List the following rock layer in chronological order starting with the oldest layer.

  10. Relative Age • In the previous slide you know rock layer Y is younger than rock layer C because _________________________________. • In the previous slide you know rock layer H is older than rock layer I because _________________________________. • In the previous slide you know rock layer X is younger than rock layers D, E, and F because _________________________________. Y cuts across C H is under I D, E, and F are included in X

  11. ____________ Age: By measuring the percentages of parent and daughter isotopes in some rocks or fossils, an age in years of that object can be determined. Absolute

  12. Fossils Picture C shows what two types of fossils, and how do they form? Picture D shows what type of fossil? Picture B shows what type of fossil? Mold-organism decays Cast-mold fills with minerals Trace fossil Actual remains

  13. Chapter 21 Review (clues on next slide) G a s t r o l i t h n d e x fo s s i l f o s s i l c o p r o l i t e a m b e r v o l u t i o n p e m n e r a i z a t i n c a s m o d

  14. Ch 21 Review (continued)

  15. Ch 21 Review (continued) ___1.Nonconformity – ___2. Angular Unconformity- ___3.Disconformity- B sedimentary over nonsedimentary C sedimentary over tilted sedimentary A sedimentary over horizontal sedimentary

  16. Ch 21 Review (continued) paleozoic ancient life end marked by many extinctions, including dinosaurs mesozoic cenozoic recent life

  17. Ch 21 Review (continued)

  18. Ch 21 Review (continued)

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