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I can: describe methods used to assign Relative ages of rock layers

Learn about the methods used to determine the relative ages of rock layers, including the use of index fossils, rock similarity, and fossil evidence. Understand how unconformities and radioactive decay can affect the dating of rock layers.

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I can: describe methods used to assign Relative ages of rock layers

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  1. I can: describe methods used to assign Relative ages of rock layers • Do Now: • How are sedimentary rocks formed? • Which fossil is the index fossil • From the picture below?

  2. Index Fossils: Fossils that are found in many places;lived for a short period of time; found in only one rock layer By comparing index fossils in various locations on Earth, it is possible to correlate(match) the relative ages of the rocks in which they appear

  3. SUPERPOSITION -The bottom rock layer is the oldest and the top layer is the youngest

  4. -Sequence of rock is a record of past events -Rock layers are ALWAYS laid down horizontally, until activities change them

  5. Relative Ageof rocks: (sequence) The age of a rock layer in comparison to its surrounding layer -Uses rock similarity, and fossil evidence

  6. What is Correlation? When geologists try to match rock layers in different locations to see if they formed at the same time. • How to correlate (match) rock layers: • Similarity of rock types • Matching index fossils

  7. Relative Ageof rocks: (sequence) 25 miles apart 1 2 3 4 5 6 1 2 3 4 5

  8. I can: Explain how unconformities cause gaps in rock layers • Do Now: • What is relative age? • How can you find the relative age • of rocks?

  9. Relative Ageof rocks: (sequence) 25 miles apart Are we able to match up all of the layers? 1 2 3 4 5 6 1 2 3 4 5 Why?

  10. Unconformities -gaps in the rock layers -occur when some rock layers are missing -three types WHY DOES THIS HAPPEN?

  11. Angular Unconformity • horizontally parallel rock layers are deposited on tilted and eroded layers

  12. 2. Disconformity Occurs between parallel layers of sedimentary rocks that have eroded and new layers have deposited on top

  13. 3. Nonconformity Occurs between sedimentary rocks and metamorphic or igneous rocks When sedimentary rock was deposited on top of eroded metamorphic or igneous rock.

  14. What type of unconformity is it?

  15. What type of unconformity is it?

  16. I can: determine the relative age of Rock layers Do Now:HW-Worksheet from webpage What type of unconformity is it? Nonconformity Sedimentary rocks Metamorphic rocks

  17. What type of unconformity is it? Disconformity

  18. What type of unconformity is it? Angular

  19. Igneous Extrusions & Intrusions Extrusion: When molten rock flows on the Earth’s surface forming an igneous rock

  20. Intrusion: Occurs when magma squeezes between rock layers beneath the Earth’s surface

  21. FOLDS AND FAULTS Folds and Faults are always younger than the original rock layers Fold: -bends in rock layers produced by movements of the earth’s crust Faults: -breaks in the rock where rock layers have shifted (earthquakes)

  22. UNIFORMITARIANISM: -The activities that shape the Earth today are the same activities that occurred in the past “The present is the key to the past”- James Hutton

  23. I can: identify how absolute age Differs form relative age Do Now:HW-take home test How is an igneous extrusion different from an igneous intrusion Igneous extrusion is when magma reaches the surface Igneous intrusion is when magma stays beneath the surface

  24. Relative Ageof rocks: (sequence) The age of a rock layer in comparison to its surrounding layer -Uses rock similarity, and fossil evidence Absolute Ageof rocks: (true age) The age of a rock layer in years -Uses radiometric dating to determine age--radioactive decay

  25. Vocabulary Review Matteris anything that takes up space and has mass Atoms – smallest unit of matter (stuff that matter is made of) -they have protons, neutrons, and electrons Element – specific kind of atom with a given number of protons

  26. Vocabulary Review Matter - water Atoms – Hydrogen and Oxygen atoms Elements – Hydrogen has 1 proton Oxygen has 16 protons Isotope – Same element Different number of neutrons

  27. Absolute age of rock layers Radioactive decay is the natural breakdown of atoms of an element that changes that element’s atoms into a new element Example: it takes 4.5 billion years for uranium 238 to change into lead 206

  28. Radioactive decay is NOT AFFECTED by temperature (heat) or pressure! Radioactive decay occurs at a constant rate known as half-life.

  29. HALF-LIFE: Half-life is the rate (time) it takes for one-half of the amount of original material to decay If we know the half-life of a radioactive material, the age of the material can be determined by measuring the amount of decayed material in the sample.

  30. Some radioactive substances have a Short half-life: Carbon 14 decays to Nitrogen 14 -Good for dating recent organic remains (between 1,000-50,0000 yrs.) 238 206 Uranium decays to Lead Long half-life: Uranium238 -Good for dating much older rocks (a very long half-life) - it takes 4.6 billion years for uranium to decay to lead

  31. Example: The amount of Carbon-14 remaining in a fossil is 0.5 grams. How old is the fossil? An equal sample of an existing organism shows the original amount of Carbon-14 was 2.0 grams. (2.0g  _____  _____) 1.How many half-lives did the sample undergo? 2.Multiply this by the half-life for Carbon-14 (5,700 years)

  32. Example: The amount of Carbon-14 remaining in a fossil is 0.5 grams. How old is the fossil? An equal sample of an existing organism shows the original amount of Carbon-14 was 2.0 grams. (2.0g  1.0g  0.5g) 1.How many half-lives did the sample undergo? 2 half-lives 2.Multiply this by the half-life for Carbon-14 Answer: 2 x 5,750 = 11,500 yrs.

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