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Relative Dating

Relative Dating. Relative Dating. Relative Age : the age of something compared to something else. Absolute Age : the actual age of a rock or an event . The Principal of Superposition. In undisturbed sedimentary rock layers (strata), the oldest rock is at the bottom. .

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Relative Dating

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  1. Relative Dating

  2. Relative Dating • Relative Age: the age of something compared to something else. • Absolute Age: the actual age of a rock or an event

  3. The Principal of Superposition • In undisturbed sedimentary rock layers (strata), the oldest rock is at the bottom. YOUNGEST rock layer OLDEST rock layer

  4. Dating Intrusions, Extrusions, & Inclusions • Intrusion: when magma squeezes into preexisting rocks and cools. • YOUNGER than any rock it cuts through

  5. Dating Intrusions, Extrusions, & Inclusions • Extrusion:when lava flows on the SURFACE and cools. • YOUNGER than rocks beneath it • OLDER than rocks above it.

  6. Dating Intrusions, Extrusions, & Inclusions • Inclusion: a piece of older rock within igneous rock.

  7. Cross-Cutting Relationships • Types of Cross-cutting relationships: Intrusions, faults, veins, etc. • These features are YOUNGER than the rocks they cut across.

  8. Cross-Cutting Relationships A fault is younger than the rock layers it cuts across An igneous intrusion is younger than the rock it penetrates

  9. Dating Rock Features The folding and tilting of rock layers are events that are younger than the rock layers they effect.

  10. Unconformity – A surface of erosion between rock layers that represents a missing gap in Earth’s history. Uplifting and folding Deposition Unconformity Subsidence Erosion

  11. Correlation • The process of showing that rock layers, or geologic events, from different places are the same, or similar in age. • Types of Correlation: • Exposed bedrock • Similarities in Rocks • Use of Index Fossils • Volcanic Ash or Meteorite Deposits

  12. 1. Correlation by Exposed Bedrock • Bedrock is usually covered with soil, but can occasionally be exposed. • Correlation can be accomplished by directly following the rock layers.

  13. 2. Correlation by Similarities in Rocks • Rocks can be correlated by having similar appearance, color, mineral composition, and rock sequence.

  14. 3. Correlation by Index Fossils • Index Fossil: a fossil that is used to date the rock layers in which it is found. • An organism that lived during a relatively short, well-defined time span. • Have a wide distribution geographically.

  15. Which of these is an INDEX FOSSIL?

  16. 4. Correlation by Volcanic Ash and Meteorite Deposits • Volcanic Ash: ash from each volcanic eruption has unique composition • Ash deposits are widely distributed, and represent a small period of time. • Meteorite Deposits: rock particles and debris produced by an asteroid, comet, or meteorite impact can cover large areas of Earth.

  17. “SEQUENCE OF EVENTS” PRACTICE WORKSHEETS

  18. Sequence 1: Uplift & Erosion • Limestone deposited • Sandstone deposited • Shale Deposited • Uplift • Erosion

  19. Sequence 2: Faulting • Limestone deposited • Sandstone deposited • Shale deposited • Faulting

  20. Sequence 3: Folding • Limestone deposited • Sandstone deposited • Shale deposited • Folding

  21. 6 5 7 4 6(erosion) 4 4 Folding 5(tilting) 3 3 3 2 2 2 1 1 1 Oldest- Shale Youngest- Folding Oldest- Shale Youngest- Siltstone Oldest- Sandstone Youngest- Shale Oldest- Limestone Youngest- Igneous Intrusion Oldest- Sandstone Youngest-IgneousIntrusion Oldest- Shale Youngest- Fault 4 4 4 6 3 3 5 3 2 2 2 5 6 5 1 1 12 1

  22. 5 4 6 3 2 7 1 Oldest- Siltstone Youngest- Igneous Intrusion link unconformity formation 13

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