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Interpreting Geologic History

Interpreting Geologic History. What happened when. Two types of dating:. Absolute Dating: Gives the exact age of a rock or a geologic event Ex. He was born on June 26 th , 1902 Dinosaurs went extinct 65.95 million years ago (true)

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Interpreting Geologic History

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  1. Interpreting Geologic History What happened when

  2. Two types of dating: • Absolute Dating: Gives the exact age of a rock or a geologic event • Ex. He was born on June 26th, 1902 • Dinosaurs went extinct 65.95 million years ago (true) • Relative Dating: Tells you the order in which rocks were created or geologic events took place • Ex. He was the 2nd of 4 children • The dinosaurs went extinct after the trilobites but before the wholly mammoths.

  3. Absolute Dating: Tree rings • Tree Rings: Every year trees leave a ring in it’s trunk. These vary on size based on the climate that year. Scientists can put together tree rings from ancient trees in an unbroken line all the way to the present. • Used very often in archaeology for dating wood beams and carvings. • Technical name is dendochronology

  4. Absolute Dating: Index fossils • Scientists can know the absolute age of rock if they are able to find certain fossils in that rock called INDEX FOSSILS • These fossils are known to have lived only during a certain period of Earth’s history, were widespread, and died out or evolved suddenly • Examples are certain kinds of shells or trilobites.

  5. Absolute Dating:Radioactive Dating • The most reliable method of absolute dating is RADIOACTIVE DATING. • When Magma cools to form an igneous rock it begins to emit radioactive particles at a constant rate. Scientists can measure how much radioactive material is left in a sample to determine when that rock first cooled from Magma. This works accurately for rocks up to 50 billion years old (far older than the age of the Earth or even the Universe)

  6. Relative Dating • Relative Dating tells scientists the order of geologic events and rock formations. • They use FOUR PRINCIPLES to guide their analysis. • We are going to discover these principles on our own.

  7. Create a 3 Color Stack of “Sedimentary Rock”

  8. The Law of Superposition • In a sequence of undisturbed rock: THE OLDEST ROCKS WILL BE AT THE BOTTOM

  9. Now, Bend or Break your rock FLOW FRACTURE Use “great pressure” (or string) to make a FAULT Use “great pressure” to bend your rocks to make FOLDS.

  10. The Law of OriginalHorizontality • Rocks are almost always laid down in flat horizontal layers. • If they are found so that they are bent or otherwise not horizontal, THE FORCE THAT BENT OR BROKE THEM MUST HAVE COME AFTER they were originally laid down.

  11. Next, use a pencil to dig a hole into your rock and fill it up with Igneous rock.

  12. The Law of Cross Cutting Relationships • An igneous rock that INTRUDES across other rock layers is YOUNGER than the layers it cuts across.

  13. Unconformities What is an unconformity? Unconformities obey the Law of Cross Cutting Relationships An unconformity and everything above it are ALWAYS YOUNGER than what they cross-cut. • An unconformity is AN UNDERGROUND ERODED SURFACE • Unconformities tell geologists that there was erosion and new layers started building on top

  14. More Unconformities http://www.classzone.com/books/earth_science/terc/content/visualizations/es2902/es2902page01.cfm?chapter_no=visualization

  15. Finally, split your rock almost into 2 and separate the sides to make a “valley”

  16. The Law of Lateral Continuity • Layers of rock extend in all directions and are the same even if separated by a valley or fault • On the other hand, rocks above or below may be very different. THERE IS MORE VARIATION BETWEEN ROCK TYPES UP AND DOWN THAN THERE IS SIDE TO SIDE

  17. Let’s try some puzzles…

  18. This one has Metamorphosis!

  19. Tricky…

  20. A little harder…

  21. Uber-difficult (extra credit)

  22. The technical name: Stratigraphy Strata: Layers Graphy: Study Stratigraphy: Study of layers Used in geology, paleontology, and archaeology to infer RELATIVE AGE of artifacts, bones, or rocks.

  23. Archaeologist What do they do? How do you become one? To become an archaeologist you need to receive a bachelors degree in geology, anthropology, history, or archeology (if offered). Almost all archaeologists have a Masters, or even a PhD. Many college students work on archaeological digs during the summer in places all around the world. Archaeology is a hard career to find a job in, perseverance is definitely required. They are paid between $37,000-55,000. • Excavate ruins of ancient cultures systematically and scientifically • Work for developers and construction companies that are required by law to check for artifacts before building • Forensic archaeologists work for the police to solve “cold cases” • Excavation can be grueling, slow and tedious. However, archaeologists can find incredible things and make amazing discoveries.

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